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【分享】太阳能电池－燃料电池研究进展系列专贴【已搜索无重复】
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Nano-Manhattan' 3D solar cells boost efficiency (Update) Unique three-dimensional solar cells that capture nearly all of the light that strikes them could boost the efficiency of photovoltaic (PV) systems while reducing their size, weight and mechanical complexity. The new 3D solar cells capture photons from sunlight using an array of miniature "tower" structures that resemble high-rise buildings in a city street grid. The cells could find near-term applications for powering spacecraft, and by enabling efficiency improvements in photovoltaic coating materials, could also change the way solar cells are designed for a broad range of applications. "Our goal is to harvest every last photon that is available to our cells," said Jud Ready, a senior research engineer in the Electro-Optical Systems Laboratory at the Georgia Tech Research Institute (GTRI). "By capturing more of the light in our 3D structures, we can use much smaller photovoltaic arrays. On a satellite or other spacecraft, that would mean less weight and less space taken up with the PV system." The 3D design was described in the March 2007 issue of the journal JOM, published by The Minerals, Metals and Materials Society. The research has been sponsored by the Air Force Office of Scientific Research, the Air Force Research Laboratory, NewCyte Inc., and Intellectual Property Partners, LLC. A global patent application has been filed for the technology. The GTRI photovoltaic cells trap light between their tower structures, which are about 100 microns tall, 40 microns by 40 microns square, 10 microns apart -- and built from arrays containing millions of vertically-aligned carbon nanotubes. Conventional flat solar cells reflect a significant portion of the light that strikes them, reducing the amount of energy they absorb. Because the tower structures can trap and absorb light received from many different angles, the new cells remain efficient even when the sun is not directly overhead. That could allow them to be used on spacecraft without the mechanical aiming systems that maintain a constant orientation to the sun, reducing weight and complexity – and improving reliability. "The efficiency of our cells increases as the sunlight goes away from perpendicular, so we may not need mechanical arrays to rotate our cells," Ready noted. The ability of the 3D cells to absorb virtually all of the light that strikes them could also enable improvements in the efficiency with which the cells convert the photons they absorb into electrical current. In conventional flat solar cells, the photovoltaic coatings must be thick enough to capture the photons, whose energy then liberates electrons from the photovoltaic materials to create electrical current. However, each mobile electron leaves behind a "hole" in the atomic matrix of the coating. The longer it takes electrons to exit the PV material, the more likely it is that they will recombine with a hole -- reducing the electrical current. Because the 3D cells absorb more of the photons than conventional cells, their coatings can be made thinner, allowing the electrons to exit more quickly, reducing the likelihood that recombination will take place. That boosts the "quantum efficiency" – the rate at which absorbed photons are converted to electrons – of the 3D cells. Fabrication of the cells begins with a silicon wafer, which can also serve as the solar cell’s bottom junction. The researchers first coat the wafer with a thin layer of iron using a photolithography process that can create a wide variety of patterns. The patterned wafer is then placed into a furnace heated to 780 degrees Celsius. Hydrocarbon gases are then flowed into furnace, where the carbon and hydrogen separate. In a process known as chemical vapor deposition, the carbon grows arrays of multi-walled carbon nanotubes atop the iron patterns. Once the carbon nanotube towers have been grown, the researchers use a process known as molecular beam epitaxy to coat them with cadmium telluride (CdTe) and cadmium sulfide (CdS) which serve as the p-type and n-type photovoltaic layers. Atop that, a thin coating of indium tin oxide, a clear conducting material, is added to serve as the cell’s top electrode. In the finished cells, the carbon nanotube arrays serve both as support for the 3D arrays and as a conductor connecting the photovoltaic materials to the silicon wafer. The researchers chose to make their prototypes cells from the cadmium materials because they were familiar with them from other research. However, a broad range of other photovoltaic materials could also be used, and selecting the best material for specific applications will be a goal of future research. Ready also wants to study the optimal heights and spacing for the towers, and to determine the trade-offs between spacing and the angle at which the light hits the structures. The new cells face several hurdles before they can be commercially produced. Testing must verify their ability to survive launch and operation in space, for instance. And production techniques will have to scaled up from the current two-inch laboratory prototypes. "We have demonstrated that we can extract electrons using this approach," Ready said. "Now we need to get a good baseline to see where we compare to existing materials, how to optimize this and what’s needed to advance this technology." Intellectual Property Partners of Atlanta holds the rights to the 3D solar cell design and is seeking partners to commercialize the technology. Another commercialization path is being followed by an Ohio company, NewCyte, which is partnering with GTRI to use the 3D approach for terrestrial solar cells. The Air Force Office of Scientific Research has awarded the company a Small Business Technology Transfer (STTR) grant to develop the technology. "NewCyte has patent pending, low cost technology for depositing semiconductor layers directly on individual fullerenes," explained Dennis J. Flood, NewCyte’s president and CTO. "We are using our technology to grow the same semiconductor layers on the carbon nanotube towers that GTRI has already demonstrated. Our goal is to achieve performance and cost levels that will make solar cells using the GTRI 3D cell structure competitive in the broader terrestrial solar cell market." On the Net: http://www-stage.gatech.edu/news-room/flash/CNTpv.html Source: Georgia Institute of Technology [ Last edited by ddx-k on 2008-12-4 at 15:44 ] |
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Platinum nanocrystals boost catalytic activity for fuel oxidation, hydrogen production (A) Low-magnification SEM image of a platinum tetrahexahedral nanocrystal and its geometrical model. (B) High-resolution transmission electron microscopy image recorded from a platinum tetrahexahedral nanocrystal to reveal surface atomic steps in the areas made of (210) and (310) sub-facets. Credit: Zhong Lin Wang A research team composed of electrochemists and materials scientists from two continents has produced a new form of the industrially-important metal platinum: 24-facet nanocrystals whose catalytic activity per unit area can be as much as four times higher than existing commercial platinum catalysts. The new platinum nanocrystals, whose "tetrahexahedral" structure had not previously been reported in the metal, could improve the efficiency of chemical processes such as those used to catalyze fuel oxidation and produce hydrogen for fuel cells. "If we are going to have a hydrogen economy, we will need better catalysts," said Zhong Lin Wang, a Regents Professor in the School of Materials Science and Engineering at the Georgia Institute of Technology. "This new shape for platinum catalyst nanoparticles greatly improves their activity. This work also demonstrates a new method for producing metallic nanocrystals with high-energy surfaces." The new nanocrystals, produced electrochemically from platinum nanospheres on a carbon substrate, remain stable at high temperatures. Their sizes can be controlled by varying the number of cycles of "square wave" electrical potential applied to them. "This electrochemical technique is vital to producing such tetrahexahedral platinum nanocrystals," said Shi-Gang Sun, an Eminent Professor in the College of Chemistry and Chemical Engineering at the Xiamen University in China. "The technique used to produce the new platinum nanostructures may also have applications to other catalytic metals." The research was supported by the Natural Science Foundation of China, Special Funds for Major State Basic Research Project of China and the U.S. National Science Foundation. Details will be reported in the May 4 issue of the journal Science. Platinum plays a vital role as a catalyst for many important reactions, used in industrial chemical processing, in motor vehicle catalytic converters that reduce exhaust pollution, in fuel cells and in sensors. Commercially available platinum nanocrystals – which exist as cubes, tetrahedra and octahedra – have what are termed "low-index" facets, characterized by the numbers {100} or {111}. Because of their higher catalytic activity, "high-index" surfaces would be preferable – but until now, platinum nanocrystals with such surfaces have never been synthesized – and therefore have not been available for industrial use. The nanocrystals produced by the U.S.-Chinese team have high energy surfaces that include numerous "dangling bonds" and "atomic steps" that facilitate chemical reactions. These structures, characterized by {210}, {730} or {520} facets, remain stable at high temperatures – up to 800 degrees Celsius in testing done so far. That stability will allow them to be recycled and re-used in catalytic reactions, Wang said. Though the process must still be fine-tuned, the researchers have learned to control the size of the particles by varying the processing conditions. They are able to control the size such that only 4.5 percent of the nanocrystals produced are larger or smaller than the target size. "In nanoparticle research, two things are important: size control and shape control," said Wang. "From a purity point of view, we have been able to obtain a high yield of nanocrystals whose shape was a real surprise." Depending on conditions, the new nanocrystals can be as much as four times more catalytically active per unit area than existing commercial catalysts. But since the new structures tested are more than 20 times larger than existing platinum catalysts, they require more of the metal – and hence are less active per unit weight. "We need to find a way to make these nanocrystals smaller while preserving the shape," Wang noted. "If we can reduce the size through better control of processing conditions, we will have a catalytic system that would allow production of hydrogen with greater efficiency." Production of the new crystals begins with polycrystalline platinum spheres about 750 nanometers in diameter that are electrodeposited onto a substrate of amorphous – also known as "glassy" – carbon. Placed in an electrochemical cell with ascorbic acid and sulfuric acid, the spheres are then subjected to "square wave" potential that alternates between positive and negative potentials at a rate of 10 to 20 Hertz. The electrochemical oxidation-reduction reaction converts the spheres to smaller nanocrystals over a period of time ranging from 10 to 60 minutes. The role of the carbon substrate isn't fully understood, but it somehow enhances the uniformity of the nanocrystals. "The key to producing this shape is to tune the voltage and the time period under which it is applied," Sun noted. "By changing the experimental conditions, we can control the size with a high level of uniformity." Scanning electron microscopy shows that the sizes average 81 nanometers in diameter, with the smallest just 20 nanometers. The microscopy also found that the structures were composed of single crystals with no dislocations. "Not only do we have a beautiful shape – which was observed for the first time in this research – but we also have a very valuable catalyst," Sun added. "And because these nanocrystals are stable, the shape is preserved after the catalytic reaction, which will allow us to use the same nanocrystals over and over again." Source: Georgia Institute of Technology |
2楼2008-11-12 23:48:30
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科技日报2007年6月27日讯 几年之前，包括东芝和NEC在内的一些日本公司宣称，他们将推出可供手机、笔记本电脑和音乐播放器使用的微型燃料电池。这种电池在需要充电时，只需往里加点酒精就行了，消费者似乎可以从此摆脱充电器的束缚，干电池时代也似乎就此宣告结束。 然而，此后则是一片寂静。直到今天，他们鼓吹的燃料电池在市场上也难觅其踪，究竟哪里出了问题？ 第一张大饼不好烙 其实这些公司也是有苦难言。他们没料到，小小的燃料电池竟然是个“难产儿”。 研究人员发现，电池内部的物质对于温度和湿度太敏感，而且容易产生一氧化碳这种有害气体。他们制造出的便携式燃料电池的最佳性能，也仅仅勉强和他们宣称要取代的锂电池相当，不具有市场竞争力。 目前，正在研制开发的燃料电池主要有两种：质子交换膜型（PEM）和固体氧化物型。两者都能使燃料和空气沿相反方向透过一层特殊的薄膜。 PEM的交换膜上涂有一层催化剂，这种催化剂能够将燃料（通常是氢原子）的电子夺走，氢原子于是成为带正电荷的氢离子，它可以透过薄膜，与另一侧来自空气中的氧结合形成水。被夺走的电荷则急于和氢离子复合，不停地向外迁移，这个过程连续下来就形成了电流。 实际上，PEM电池从上世纪60年代就已经开始使用，它可以在170℃下工作，这是一个还可以接受的温度。但PEM电池有一个致命弱点：它需要纯氢来产生电子，目前还没有人能找到一个经济可行的方法来做到这一点。这迫使许多开发PEM电池的厂商把目光转向甲醇。比较而言，甲醇当然是价廉易得，但它含能量较低，是一个弱的能量来源。 固体氧化物型的工作原理则恰好相反。空气中的氧原子渗透到膜的另一侧，和被夺走电子的氢原子及一氧化碳结合，形成水和二氧化碳。因为要在1370℃这样的高温下工作，固体氧化物电池一度被开发者放弃。但它可以使用密度更高的碳氢化合物（如丁烷）作燃料，因而能提供远高于PEM电池的动力。在液态下，丁烷的能量密度是7.4千瓦时/升，而甲醇只有4.4千瓦时/升，锂电池通常只能提供0.3千瓦时的电量。 MIT三精英联手再战 美国马萨诸塞州的理利普申公司最近宣布，他们制造出一种火柴盒大小的燃料电池，可以供笔记本电脑使用几天。这种燃料电池采用的是固体氧化物设计，以丁烷为燃料。 理利普申（Lilliputian，意思为小人儿）公司成立不过4年，公司的两位创始人撒穆尔•斯凯威兹和阿列克斯•弗远兹都来自麻省理工学院（MIT）。在上世纪90年代，他们曾经在MIT做过用顶针大小的反应器蚀刻硅晶元的实验，不过那只是纯理论性的研究。后来他们意识到，可以利用类似的微机械技术来建立微小的“转化器”，从酒精中分离出纯氢供燃料电池使用。于是他们离开MIT，创建了理利普申公司。 肯尼思•拉扎勒斯则是一位在MIT受训过的航空学工程师，他把自己的公司以3500万美元的价格卖掉后一直再想找点事干。2003年底，拉扎勒斯遇见了斯凯威兹和弗远兹，当时这哥儿俩正在只有一个房间的实验室里埋头苦干，他们对拉扎勒斯把热门技术变成商业产品的本领极为佩服，力邀他担任理利普申的 CEO。 三位来自MIT的精英一起开始研究微型PEM燃料电池，很快就遇到了现在仍困扰日本同行的难题：以酒精为燃料的电池不能产生足够的电量，因此难以和锂电池竞争。于是，他们决定在固体氧化物电池上下功夫。他们面临的最大挑战之一就是如何将陶瓷电解质和硅晶整合在一起，因为当受热时，陶瓷的膨胀速度是硅的 4倍。他们是如何解决这个难题的？这当然是商业秘密。不过他们承认使用了一个网状断裂结构来吸收压力，与人行道上一块块地砖之间的膨胀连接很相似。 另一个要克服的难题是，在一个微小的空间内如何保持巨大的热量？部分热量是有用的，它可以把丁烷分解成氢和一氧化碳，从而使电池中的反应持续进行。为此，他们设计了一个真空罩，装在整个装置的上部，就像玻璃球包裹着钨丝的电灯泡一样。 由于采用了独特的设计，电池摸上去才刚刚温热。拉扎勒斯说：“如果要想在电池行业的竞争中胜出，你必须在电池的能量密度上击败对手，而丁烷是已知的能量密度最高的燃料之一。而我们的电池克敌致胜的另一个法宝是把热量保存在里面，这简直是个设计上的奇迹。” 争雄市场看实力 在几年前就嚷嚷着要推出燃料电池的工业巨头最近又在发誓说，他们的电池就要大规模投产了。2005年，东芝公司展出了用于音乐播放器和其它设备的甲醇燃料电池，他们计划在明年推向市场。机械技术公司已经重新聘用吉列公司来开发甲醇燃料盒，并与三星公司达成协议来制造样机，希望在2008年就能推到市场上销售。 对此，理利普申公司早已成竹在胸。他们的燃料电池已经获得了国际民航组织和联合国危险材料运输管理部门的批准，今年年底可望获得美国运输部的批准。打火机一直被禁止带上飞机，因为燃料丁烷和打火石是在一个装置内。而理利普申的电池里的丁烷几乎不可能被点燃，除非你将电池砸碎，同时点燃一根火柴。 拉扎勒斯估计，他们公司的第一个产品将是专供笔记本电脑和智能手机使用的便携式充电电池，2美元一罐的丁烷燃料可以“充电”25次。虽然还没有宣称和哪个制造商达成大规模生产的协议，但拉扎勒斯对此非常乐观，因为迄今为止，他已经从阿特拉斯、美国硅谷顶级风险投资公司及其它风险投资基金那里筹集了 4000万美元。他们还有另一个优势，制造他们的燃料电池所需要的是已经具有20年历史的半导体制造设备，这些设备在亚洲各地都有。 今天，纳米技术飞速发展，我们没有理由怀疑，将来有一天燃料电池会变得像跳蚤一样大小，依靠这种电池供电的可注射传感器及各种微型医疗器械将出现在我们的生活中。 图为燃料电池芯片的内部构造。电池的能量来源———丁烷在燃料处理器中被转化成氢和一氧化碳，它们沿着在硅晶上蚀刻出的微管进入燃料电池阵列。在每一个阵列单元里，催化剂夺走燃料的电子，而空气中的氧则透过电解质薄膜带来补充电子，于是产生电流，副产物是水和二氧化碳。 来源: http://www.stdaily.com/gb/stdaily/2007-06/27/content_687488.htm |
3楼2008-11-12 23:49:49
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Portugal – June 28, 2007 – A new paper published in Journal of the American Ceramic Society proposes a new method of producing hydrogen for portable fuel cells. This new method negates the need for the complicated and expensive equipment currently used. With their ability to work steadily for 10-20 times the length of equivalently sized Lithium-ion batteries, portable fuel cells are ideal energy suppliers for devices such as computers, cell phones and hybrid vehicles. Significant amounts of hydrogen are needed to power these long-lived fuel cells, but producing the chemical has, until this point, been costly and difficult. Zhen-Yan Deng, lead author of the study, found that modified aluminum powder can be used to react with water to produce hydrogen at room temperature and under normal atmospheric pressure. The result is a cost-efficient method for powering fuel cells that will make their use a more practical and realistic option in many applications. Efforts to produce large amounts of hydrogen for portable devices have previously focused on other chemicals; however, compared to other hybrids, aluminum is cheaper and requires no other chemical in order to react with water. “This makes the modified aluminum powder a more economically viable material to generate hydrogen for the future use of portable fuel cells,” says Deng. Link: http://www.blackwellpublishing.com/press/pressitem.asp?ref=1308 |
4楼2008-11-12 23:50:14
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Inexpensive Bio-Inspired Materials That Could Make Hydrogen Fuel Cells Feasible from Science Daily — Scientists at Pacific Northwest National Laboratory will receive $1.98 million from the U.S. Department of Energy over the next three years to emulate nature's use of enzymes to convert chemicals to energy, PNNL announced Wednesday (June 6). The information that scientists at the DOE national lab turn up may point to new materials that render it economically feasible to produce energy from hydrogen fuel cells. "This is a basic research project, but one that we hope will provide new knowledge that will be pertinent to the production of hydrogen or oxidation of hydrogen in fuel cells," said Morris Bullock, co-leading the project with Dan DuBois. Both Bullock and DuBois are members of the Molecular Interactions and Transformations group and the Institute for Interfacial Catalysis at PNNL. Bullock noted that an electrocatalytic reaction, or energy made by catalytic oxidation of hydrogen in fuel cells, "is very attractive for many applications." But so far, such chemical conversions are expensive; fuel cells require the precious metal platinum. "We seek to prepare new metal complexes based on abundant, inexpensive metals such as iron, manganese and molybdenum." To search for electrocatalyst alternatives to platinum, the team will be guided by natural systems like those in species of bacteria and algae that enlist hydrogenase enzymes in energy production. Bullock and colleagues hope "to replicate the function but not the exact structure" of the natural enzymes. Recent structural studies of hydrogenase enzymes from these microorganisms have revealed that sites where electrocatalysis takes place contain nuclei made up of iron-iron or nickel-iron complexes. These enzymes' high catalytic activity suggests that properly designed synthetic catalysts based on inexpensive metals can be used in fuel cells for this important energy-conversion reaction in place of platinum. The PNNL award is among 13 basic-research projects funded by $11.2 over the next three years by the Basic Energy Sciences program of the DOE Office of Science. The research aims to overcome challenges associated with the production, storage and use of hydrogen. Note: This story has been adapted from a news release issued by DOE/Pacific Northwest National Laboratory Science Daily — Scientists at Pacific Northwest National Laboratory will receive $1.98 million from the U.S. Department of Energy over the next three years to emulate nature's use of enzymes to convert chemicals to energy, PNNL announced Wednesday (June 6). The information that scientists at the DOE national lab turn up may point to new materials that render it economically feasible to produce energy from hydrogen fuel cells. "This is a basic research project, but one that we hope will provide new knowledge that will be pertinent to the production of hydrogen or oxidation of hydrogen in fuel cells," said Morris Bullock, co-leading the project with Dan DuBois. Both Bullock and DuBois are members of the Molecular Interactions and Transformations group and the Institute for Interfacial Catalysis at PNNL. Bullock noted that an electrocatalytic reaction, or energy made by catalytic oxidation of hydrogen in fuel cells, "is very attractive for many applications." But so far, such chemical conversions are expensive; fuel cells require the precious metal platinum. "We seek to prepare new metal complexes based on abundant, inexpensive metals such as iron, manganese and molybdenum." To search for electrocatalyst alternatives to platinum, the team will be guided by natural systems like those in species of bacteria and algae that enlist hydrogenase enzymes in energy production. Bullock and colleagues hope "to replicate the function but not the exact structure" of the natural enzymes. Recent structural studies of hydrogenase enzymes from these microorganisms have revealed that sites where electrocatalysis takes place contain nuclei made up of iron-iron or nickel-iron complexes. These enzymes' high catalytic activity suggests that properly designed synthetic catalysts based on inexpensive metals can be used in fuel cells for this important energy-conversion reaction in place of platinum. The PNNL award is among 13 basic-research projects funded by $11.2 over the next three years by the Basic Energy Sciences program of the DOE Office of Science. The research aims to overcome challenges associated with the production, storage and use of hydrogen. Source: DOE/Pacific Northwest National Laboratory. |
5楼2008-11-12 23:50:46
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A startling discovery on the development of human embryonic stem cells by scientists at McMaster University will change how future research in the area is done. An article published in the prestigious scientific journal Nature this week reports on a new understanding of the growth of human stem cells. It had been thought previously that stem cells are directly influenced by cells in the local environment or ‘niche’, but the situation may be more complex. Human embryonic stem cells are perpetual machines that generate fuel for life. In this week’s Nature, researchers of the McMaster Cancer and Stem Cell Research Institute show that human embryonic stem (ES) cells can actually produce distinctive niche cells, which then release stem-cell nourishing proteins to help keep their ‘parents’ ticking over. Scientific Director Mick Bhatia and colleagues provide the first evidence that human ES cells have the unique ability to generate human-ES-cell-derived fibroblast-like niche cells (hdFs) in vitro despite removal from their in vivo microenvironment. These hdFs then provide a continuous source of supportive proteins, including insulin-like growth factor 2 (IGF-II), which they now show could be “the” protein to sustain hESCs.. Researchers are interested in the relationship between stem cells and their niche, because the niche represents a route for modifying stem cell behaviour — if human ES cells can be reliably guided down a particular pathway, then they can be more readily used for future clinical therapy to regenerate damaged tissue such as neurons for Parkinson’s disease, or insulin producing cells for diabetes . The research has been funded by the Canadian Institutes for Health Research and the National Cancer Institute of Canada. The Nature article is the latest in a series of important papers published by scientists at the 18-month-old institute, which was established with funding by philanthropist Michael G. DeGroote. The institute has a research focus on the molecular determinants of cancer and tissue repair and is building scientific momentum. “This discovery of a new fundamental understanding about how human stem cells develop is the kind of scientific work which has already put this Institute on the map as the leader in this field,” said John Kelton, dean and vice-president of McMaster’s Faculty of Health Sciences. Mick Bhatia said that he and his scientific team have been working for the past year to prove themselves wrong, but as every test confirmed their discovery, it was time to submit the work for international peer review from other experts. “This will be critical for future developments involving drug and gene screening of human ES cells, that will be required before clinical use of human stem cells of this kind,” he said. Stem cells, which have the ability to turn into many different types of cells, have been the subject of intense study for the past two decades, as scientists have been gradually deciphering the processes by which unspecialized stem cells become the many specialized cells types in the body. The new discovery about how human ES cells grow and multiply will create a paradigm shift in how scientists conduct future research, which could someday lead to new therapies for various illnesses. "The fact that there is a niche for human ES cells, I think, changes how any regenerative medicine that starts with human ES cells would ever occur," said Bhatia. "If at their most fundamental level, human embryonic stem cells themselves are producing a cell that regulates their decisions on future differentiation, one way of controlling differentiation would be to control the niche." Source: McMaster University |
6楼2008-11-12 23:51:03
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教育部科技发展中心2007年7月18日报道 美国加州大学SantaBarbara分校（UCSB）聚合体和有机固体中心的科学家们的诺贝尔奖获得者、物理学教授Alan Heeger同韩国的KwangheeLee及其他科学家们合作，制造出了一种新型级联高效有机太阳能电池。他们的结果发表在最新一期的《Science》上。 及联电池由两个多层部分组成，来收集更宽范围的太阳辐射——从短波长到长波长。Heeger说：“我们得到了6.5%的效率。这是目前为止使用有机材料制造的太阳能电池获得的最高效率。我十分确信我们能够进一步改进它使其效率能够制造商用产品。”他预期3年内这种技术将投放市场。 Heeger和Lee已经在研发太阳能电池上有多年的合作。他们发明的这种及联电池既提高了效率又降低了成本。他们说：“这种技术，能够使用成本低廉的印刷和被覆技术大面积地把有电池的效材料同时成型在轻柔的基底上。” 多层的装置等价于多个串联的电池。通过溶液加工沉积制造每一层使电池的成本变低。 作者们在文中说：“及联太阳能电池把两个不同吸收特性的电池连接在一起来收集更宽范围的太阳光谱。它的每一层都是从含有体异质结（包括半导体聚合体、富勒烯衍射物）的溶液中制造出来的。” 电池被TiOx材料（一种透明的钛氧化物）分隔并连接。这是这个多层系统具有高效率的关键因素。TiOx传导电子并在第一个电池中作为收集层，而且还能作为制作第二个电池时的稳定的基底。 |
7楼2008-11-12 23:51:23
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Researchers at New Jersey Institute of Technology have developed an inexpensive solar cell that can be painted or printed on flexible plastic sheets. “The process is simple,” said lead researcher and author Somenath Mitra, PhD, professor and acting chair of NJIT’s Department of Chemistry and Environmental Sciences. “Someday homeowners will even be able to print sheets of these solar cells with inexpensive home-based inkjet printers. Consumers can then slap the finished product on a wall, roof or billboard to create their own power stations.” “Fullerene single wall carbon nanotube complex for polymer bulk heterojunction photovoltaic cells,” featured as the June 21, 2007 cover story of the Journal of Materials Chemistry published by the Royal Society of Chemistry, details the process. Harvesting energy directly from abundant solar radiation using solar cells is increasingly emerging as a major component of future global energy strategy, said Mitra. Yet, when it comes to harnessing renewable energy, challenges remain. Expensive, large-scale infrastructures such as wind mills or dams are necessary to drive renewable energy sources, such as wind or hydroelectric power plants. Purified silicon, also used for making computer chips, is a core material for fabricating conventional solar cells. However, the processing of a material such as purified silicon is beyond the reach of most consumers. “Developing organic solar cells from polymers, however, is a cheap and potentially simpler alternative,” said Mitra. “We foresee a great deal of interest in our work because solar cells can be inexpensively printed or simply painted on exterior building walls and/or roof tops. Imagine some day driving in your hybrid car with a solar panel painted on the roof, which is producing electricity to drive the engine. The opportunities are endless. ” The science goes something like this. When sunlight falls on an organic solar cell, the energy generates positive and negative charges. If the charges can be separated and sent to different electrodes, then a current flows. If not, the energy is wasted. Link cells electronically and the cells form what is called a panel, like the ones currently seen on most rooftops. The size of both the cell and panels vary. Cells can range from 1 millimeter to several feet; panels have no size limits. The solar cell developed at NJIT uses a carbon nanotubes complex, which by the way, is a molecular configuration of carbon in a cylindrical shape. The name is derived from the tube’s miniscule size. Scientists estimate nanotubes to be 50,000 times smaller than a human hair. Nevertheless, just one nanotube can conduct current better than any conventional electrical wire. “Actually, nanotubes are significantly better conductors than copper,” Mitra added. Mitra and his research team took the carbon nanotubes and combined them with tiny carbon Buckyballs (known as fullerenes) to form snake-like structures. Buckyballs trap electrons, although they can’t make electrons flow. Add sunlight to excite the polymers, and the buckyballs will grab the electrons. Nanotubes, behaving like copper wires, will then be able to make the electrons or current flow. “Using this unique combination in an organic solar cell recipe can enhance the efficiency of future painted-on solar cells,” said Mitra. “Someday, I hope to see this process become an inexpensive energy alternative for households around the world.” Source: New Jersey Institute of Technology |
8楼2008-11-12 23:51:53
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Materials scientists from Spain and the UK have made acathode material that allows solid oxide fuel cells (SOFCs) to be usedat lower temperatures. [点击图片可在新窗口打开] Albert Tarancón and colleagues at the University of Barcelona, and Imperial College, London found that the oxide GdBaCo2O5+? performed very well in the temperature range 500-700 °C. SOFCsconsist of three main components: an anode, cathode and electrolyte.The cathode catalyses the reduction of oxygen at its surface and allowsions to be transported to the electrolyte. At the anode, the fuel (forexample, hydrogen) is oxidised. "Its structural characteristics suggest a new family of SOFCs cathode materials based on layered perovskites" - Albert Tarancón, University of Barcelona Loweringthe temperature that SOFCs operate at reduces costs and improvesdurability. However, the cathode performance is the limiting factorwhen lowering the temperature. New cathode materials with highercatalytic activities are needed, in which the oxide ions are able todiffuse easily.According to Tarancón, the oxygen transportproperties and electrical performance of the perovskite-structuredoxide were comparable to other excellent cathodes. He also suggestedthat 'its structural characteristics suggest a new family of SOFCscathode materials based on layered perovskites'. Peter Slater, amaterials chemist at the University of Surrey, Guildford, UK, praisedTarancón's research, saying 'they elegantly demonstrate high oxygensurface exchange properties, along with low activation energies forboth surface exchange and oxide ion diffusion' and agreed that thefamily has great promise as cathode materials. Susan Batten Link to journal article Layered perovskites as promising cathodes for intermediate temperature solid oxide fuel cells Albert Tarancón, Stephen J. Skinner, Richard J. Chater, F. Hernández-Ramírez and John A. Kilner, J. Mater. Chem., 2007 DOI: 10.1039/b704320a Source: Chemistry Wolrd |
9楼2008-11-12 23:53:02
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Marc Reisch AS THE WORLD increasingly looks to solar power as anew source of energy, technology advances and new cooperationagreements among photovoltaic industry leaders promise to increase thesupply, processibility, and cost-efficiency of silicon-based solarenergy cells. Using new technology, Wacker Chemieplans to build a solar-grade granular polysilicon production facilityat its site in Burghausen, Germany. The 650-metric-ton-per-year plantshould come on-line at the end of 2008 and will manufacture thepolysilicon used to make solar wafers in a continuous fluidized-bedprocess. [点击图片可在新窗口打开] Wacker Chemie New process yields easier route to polysilicon for solar cells. The firm first announced two years ago that it had developed theprocess as an alternative to the batch production procedure now morewidely used to make polysilicon for both semiconductors and solarcells. The starting material, trichlorosilane, is the same for bothbatch and continuous processes. In the batch process, trichlorosilane is deposited at hightemperature on a starter rod, where it decomposes to polysilicon.Workers then remove the rods from the reactor, transfer them tocrushing machines that create manageable polysilicon pieces, and runthe pieces through an acid-etching step to remove contaminationintroduced during crushing. The continuous process eliminates the rodremoval, crushing, and etching steps. Taking its advances in solar polysilicon a step further, Wacker also says it is in talks with Schott Solar,a German maker of photovoltaic components, to set up a 50-50 jointventure to make silicon ingots and solar wafers, precursors for theproduction of solar cells. The two hope to conclude discussions andstart up production later this year. Separately, Germany's Q-Cells,which claims to be the world's second-largest maker of silicon solarcells, has increased its stake in a smaller U.S. silicon cell maker, Solaria,from 12% to 33%. Q-Cells acquired its increased stake in the SiliconValley-based firm as part of a $50 million investment it made togetherwith two financial investors and Moser Baer, an Indian maker ofphotovoltaics. Along with the investment, Q-Cells committed to supplying Solariawith enough cells to generate 1.35 gigawatts of power over the next 10years. Using its "cell multiplication technology," Solaria will doublethe output of cells it obtains by slicing them into thin strips andreassembling them to double the surface area they cover. The technologyincludes packaging the cells under an optical concentrator to focusmore sunlight on them. DuPontis also doing its part to improve solar-cell efficiency. The firm willmanage prototype development and testing of a solar cell designed bythe University of Delaware thathas the potential to be 30% more efficient than existing solar cells.The U.S. Defense Advanced Research Projects Agency awarded aDuPont/University of Delaware consortium $12 million to advancesolar-panel development, but it could award as much as $100 millionover the three-year life of the project. Source: Chemical & Engineering News |
10楼2008-11-12 23:54:11
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科研人员认为粉红色太阳能电池捕获阳光的效率更高 [作者:雅龙] [发布时间:20070801] [来源:http://www.physorg.com/news105029887.html 中国科学技术信息研究所加工整理] 据physorg网2007年7月30日报道，据俄亥俄大学研究人员称，当生产对地球环境友好的太阳能时，粉红色可能是一种新的“绿色颜色”。科学家们开发出一种新的染料敏化太阳能电池（DSSCs）。该电池所使用的红色染料和白色金属氧化物粉末混合物呈现出粉红色，可以捕获太阳光。 俄亥俄大学化学副教授吴翼鹰（音译）称，目前这些新粉红色材料是最好的光电转换材料，尽管转换效率仅为投入商业应用的硅太阳能电池的一半，但是其成本仅为硅太阳能电池的四分之一。吴正希望该材料太阳能电池能够甚至表现得更好。他说，“我们相信某天，染料敏化太阳能电池的效率可以达到其它太阳能电池的水平。染料敏化太阳能电池的最主要优势在于成本非常低。那就是我们对染料敏化太阳能电池感兴趣的原因，这一点非常重要。” 粉红色是染料敏化太阳能电池最典型的颜色。大多数染料都包含有钌，钌是红色的。与红色染料混合成粉红色的最常用金属氧化物粉末是钛氧化物或者锌氧化物，这两种金属氧化物都是白色的。但是吴教授制造的材料却具有更为新颖的色彩，他正在使用了更为复杂的金属，探索不同的粒子形状，以便提升光电转换量。 在《美国化学学会》杂志最近的一期中，他和他的研究小组发表了一篇有关他们使用锌锡酸盐制造新型染料敏化太阳能电池材料的论文。 这是研究人员首次使用非单一氧化物制造染料敏化太阳能电池。吴教授和他的同事们选择锌锡酸盐是因为锌锡酸盐属于具有可调特性复杂氧化物系列。他说，“这使未来剪裁染料敏化太阳能电池特性成为可能。” 为什么染料敏化太阳能电池是粉红色，而不是像硅太阳能电池一样的蓝色呢？ 吴教授解释到，这些传统太阳能电池呈现出蓝色是因为抗反射覆盖层的原因。这些覆盖层改善了对绿光的吸收，绿光是太阳能光谱中能量最强的光。吴教授研制物材料并没有抗反射覆盖层。 颜色决定了太阳能电池能够捕获的光的波长，因此修改颜色可以让科学家对太阳能电池的特殊特性进行优化。目前，在开发染料敏化太阳能电池中，科学家们使用红色钌染料获得了最佳效果。 吴教授说，“如果你希望获得最佳效率，你就需要考虑到你能够获得的电压和电流。”电压是一种材料能够提供的潜在能量；电流是材料能够传输的电荷数量。他说，“如果你能够吸收一个非常宽范围内的波长，那你就会不得不牺牲电压。如果你吸收到的能量极限非常高，你就可以获得高电压，但是你又不得不牺牲电流。我们的想法就是找到某个平衡点。” 自二十世纪六十年代以来，硅太阳能电池就已经出现。科学家们自二十世纪九十年代开始开发染料敏化太阳能电池。在染料敏化太阳能电池中，染料分子覆盖住了微小金属氧化物粒子，并一起被塞入一个薄膜中。染料分子捕获光能，释放电子，而金属氧化物粒子却更像是电线，将电子传输到电路之中。 但是电子可能在粒子之间传输时流失。那就是吴教授正在设计将微小纳米线进行合并，以便将电子直接传输到电路中的原因。去年，他和他的研究小组在《物理化学B》杂志上发表了一篇论文，描述了包含粒子和钛氧化物纳米线的染料敏化太阳能电池。这种染料敏化太阳能电池的效率为8.6%，约为投入商业应用的硅太阳能电池15%效率的一半。 在《美国化学学会》杂志上发表的新论文中，他们介绍了一种使用锌锡酸盐粒子的染料敏化太阳能电池，但是这种电池没有使用纳米线，其效率是3.8%。现在他们正在对这两种战略进行结合的研究，即利用锌锡酸盐和其它氧化物制造纳米线。 他们同时还在探索使用纳米树的可能性——纳米线的形状像树枝一样。吴教授说，“我们问我们自己，哪种结构才是吸收光和传输电流的最好结构呢，那就是树形结构！树叶提供了很大的捕获光的表面面积，树枝将营养传输到根部。在我们的染料敏化太阳能电池设计中，覆盖染料的粒子将提供表面面积，纳米树将在这些树叶之间长出枝条，传输电子。” 因此未来染料敏化太阳能电池中将生长一棵微小粉红色的“树”，但是其它颜色也有可能。研究人员正在研究能够工作得更好的新染料和染料化合物。 英文原文链接参见：http://www.physorg.com/news105029887.html 本消息为中国科技信息网独家报道，转载请注明出处：中国科技信息网Chinainfo。否则，将保留追究其法律责任的权利。 http://www.chinainfo.gov.cn/data/200708/1_20070801_158915.html |
11楼2008-11-12 23:54:42
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06 August 2007 Carbon nanotube scaffolds that can support bacterial cells could be used as electrodes in microbial fuel cells. Francisco del Monte and María Ferrer at the Madrid institute of materials science (ICMM-CSIC), Spain, and colleagues made multi-wall carbon nanotube scaffolds with a micro-channel structure in which bacteria can grow. 'Proteins and enzymes immobilized on carbon nanotubes (CNTs) have been used as biosensors and in methanol fuel cells. Given that CNTs are also suitable supports for cell growth, one could also use them as CNT-based electrodes in microbial fuel cells,' said del Monte. Microbial fuel cells work on the basis that bacteria can produce either hydrogen or electrons by oxidising compounds from, for example, waste water, thus generating electricity using a cathode-anode system. [点击图片可在新窗口打开] Del Monte's team tried to grow bacteria on the scaffolds by two different means 'Efficient electron transfer between the bacteria and the anode (for example, via a biofilm on the nanotubes) seems to play a major role in the performance of the fuel cell. To further enlarge the electrode surface exposed to the bacterial medium - and, hence, the energy conversion - the preparation of three-dimensional architectures through which bacteria can grow and proliferate will further improve the performance of this sort of device,' explained del Monte. Del Monte's team tried to grow bacteria on the scaffolds by two different means: by direct soaking in a bacterial culture medium and by the immobilisation of nutrient-containing beads prior to scaffold preparation. The former approach provided a higher bacteria population, but only in a few layers at the surface of the scaffold, while the latter colonized the whole of the nanostructure. 'Given that full colonisation is highly desirable,' del Monte maintained, 'we are currently focused on the improvement of bacterial viability during the scaffold formation process.' Claudio Della Volpe, a physical chemist from the University of Trento, Italy, said the strengths of del Monte's approach lie in its simplicity and the speed and efficiency of the encapsulation of the bacteria in a three-dimensional structure. 'However,' he added, 'the structure does not possess an active transfer mechanism for the processing of material and relies on diffusion, which is intrinsically slow.' Michael Spencelayh Link to journal articleBiocompatible MWCNT scaffolds for immobilization and proliferation of E. coli María C. Gutiérrez, Zaira Y. García-Carvajal, María J. Hortigüela, Luis Yuste, Fernando Rojo, María L. Ferrer and Francisco del Monte, J. Mater. Chem., 2007, 17, 2992 DOI: 10.1039/b707504a Source: Chemistry World |
12楼2008-11-12 23:55:36
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利用纳米花瓣来提高太阳能电池的性能，Nanoflower improves solar cellZ 【纳米科技世界快讯】据欧洲纳米技术网报道，A flower-shaped photoanode can improve the energy conversion efficiency of dye-sensitised solar cells (DSSCs) by 90% compared with conventional anodes made of rod-shaped structures. The new result comes from researchers at the Institute of Microelectronics and the Nanyang Technological University, both in Singapore. The technique could be used to make flexible DSSCs, says the team. The photocatalytic activity of nanostructured semiconductor films can be exploited to make the anodes in solar cells. Of particular importance is the DSSC, which uses nanostructured titanium dioxide (TiO2) films modified with sensitising dyes. When exposed to light, electrons from the dye molecules are transferred to the conducting band in the TiO2 layer, thus producing a current. Such cells are appealing because dyed nanoparticles have a great potential for absorbing light and generating electrons and because they are cheap and easy to make. [点击图片可在新窗口打开] j)c.uA;}e,T0Zc} Schematic of upstanding nanorod (a) and flowerlike (b) arrays shone under light. Credit: Appl. Phys. Lett. Recently, scientists have become interested in using zinc oxide (ZnO) because of its wide direct band gap of 3.37 eV and high electronic mobility. In theory, a dense network of ZnO nanowires or nanorods should favour electron collection because the nanowires/rods provide more direct conduction paths for electrons. Unfortunately, however, DSSCs made from upstanding ZnO nanorods so far suffer from a low "fill factor" – which is related to the maximum power the cell can supply – because of large surface recombination of electrons and holes. They also have a low photocurrent due to poor light absorption. This is because the dye loading is low and some photons fall on the gap between adjacent nanorods and so are not absorbed by the dye layer. Now, Changyun Jiang and colleagues have replaced the upstanding ZnO nanorod structure with a "nanoflower" array instead (see figure). The random branches of the nanoflowers have a larger surface area and increased light-dye interactions, leading to better light absorption. Moreover, electron-hole recombination is reduced, resulting in a much improved fill factor and an energy conversion efficiency of 1.9% – compared to just 1% for the nanorod arrays. 纳米科技世界论坛, Nanoscience and Nanotechnology World"M/T lja/e PS;u;e Laboratory of Organic/Polymer Devices Research and Development at the Institute of Microelectronics, Singapore. Credit: C. Y. Jiangw The researchers grew their nanoflower arrays on transparent indium tin oxide glass using a low temperature hydrothermal technique. "This method is simpler and cheaper than other technologies such as silicon solar cells and inorganic thin film solar cells," Jiang told nanotechweb.org. "The low temperature process also means that flexible solar cells can be made." The team now plans to further improve the light-to-electricity power conversion efficiency of DSSCs based on its nanoflower electrode and develop solid-state DSSCs with ZnO nanoflower films fabricated on flexible substrates. Researchers reported their work in Appl. Phys. Lett. 90 263501.www.nanost.net w Source： nanotechweb.org |
13楼2008-11-12 23:56:48
纸电池的发展空间到底有多大？
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科技日报2007年8月29日讯 由美国伦斯勒理工学院的几位科学家研制出来的一种薄如纸片，可剪裁、能折叠的轻型“纸电池”最近引起了人们的关注。研究者认为，由于这种纸电池具有诸多的性能，因此将会成为一种新型的能源存储设备。 那么，这种新型纸电池会对我们的生活产生怎样的影响？它的发展空间到底有多大？这些话题或许还有待科学家们的进一步探讨。 新纸电池性能独特 与传统电池相同，这种新型电池的组成部分也包括电极、电解液和隔离膜。具体而言，这种新型的纸电池是由植入了电极和电解液的纤维素纸构成，其中纤维素纸就起到了隔离物的作用。电极分别是加入纤维素中的碳纳米管和覆盖在纤维素制成的薄膜上的金属锂；而电解液就是六氟磷酸锂溶液。美国伦斯勒理工学院的科学家就是通过把电池的三部分综合到薄薄的一张纸上，而制成了这种新型纸电池。 研究显示，在2伏的电压下，这种新型纸电池每克能产生10毫安的电流。据介绍，这种新型的电池除了制作方法创新外，还具有很多重要的特性，比如说柔韧性。这种新型的纸电池由于成分主要是纤维素，因此保持了纸的一些特性，具有较好的柔韧性。根据实验显示，这种电池对温度的适应能力相当强，在-70℃至 150℃的温度区间都能正常使用。 目前不会取代锂电 一些报道称，这种新型纸电池有望替代现在消费电子用品领域常用的锂电池，专家对此将作如何解释呢？ 哈尔滨工业大学理学院应用化学系的孙克宁教授认为，每一种电池都是根据不同的需要而特别设计和发明的。由于不同的电池有不同的特性，所以某一种电池不可能是万能的，这种新型纸电池也不例外。 新型纸电池作为一种新概念电池，运用前景肯定是有的。但是从目前公布的纸电池的生产方法上看，生产这种纸电池所需要的碳纳米管的生产成本很高，不适合大批量生产，因此其实用性也是有限的。目前还只能把这种新型纸电池定位为一种探索性研究发明。由于工艺和其他方面的原因，它并不能替代广泛使用的其他种类的电池，也不可能在短时间内占有市场。 哈尔滨工业大学理学院应用化学系胡信国教授也认为，由于活性物质的量是很有限的，因此，纸电池的容量也是很小的，距离商业化应用还有很长的路要走。 至于纸电池会不会取代目前广泛使用的锂离子电池，孙克宁认为，锂离子电池的发展空间仍然是很大的，随着环保材料的开发使用和成本的不断降低，锂离子电池在未来的充电电池领域仍然占有广泛的市场。 电池污染有待解决 传统的电池由于其采用的原料关系，对环境和人体都有较大危害。据孙克宁介绍，镉镍电池是一种可充电的碱性干电池，广泛用于便携式电动工具、电动剃须刀和电动牙刷等。其生产原料中，镉是一种人体不需要的元素，射入人体会产生镉慢性中毒，时间长了会出现骨痛病，表现为骨软化，甚至卧床不起。镍在水体中的含量每升水不能超过0.1毫克，但是一节镍氢电池一般含4—8克的镍。镍镉电池在水体中如果发生泄漏将对水体产生怎样的污染可想而知。同时镉镍电池在处理上也要相当注意，一节五号镍镉电池可以污染一平方米以上的土地。 锂离子电池是目前在手机、笔记本电脑等电子产品中广泛使用的一种充电电池。据胡信国介绍，锂离子电池的正极为钴酸锂，负极为石墨，电解液为六氟磷酸锂的有机电解液，这些材料对人体没有太大毒性，因此被国内外称为绿色电源。但是，由于钴酸锂的化学活性很高，锂离子电池也存在安全性问题。 同时，孙克宁也指出，锂离子电池虽然不含汞、镉、铅等毒害大的重金属元素，但是它也会对环境造成污染。主要体现在其电解质进入环境后，可发生化学反应，造成氟污染和有机污染。总而言之，传统的充电电池会对水体和农田产生巨大污染，并且这种污染是不可逆的和长时期的。同时还会直接或者是通过环境对人体健康产生不同程度的危害，所以科学家从来没有停止过对新型环保电池的研究。 就新型纸电池而言，由于这种电池的成分以纤维素为主，可能使人们联想到它与一般的电池不同，对环境没有危害。但是，孙克宁指出，这种新型纸电池虽然在生产过程中没有污染，但是其电池的处理仍然可能产生污染。从公布的研究论文看，其电解液是六氟磷酸锂，这种物质对环境是有污染的。并且在电解质不变的情况下，其对环境的污染与一般的锂离子电池并没有很大区别。而胡信国则认为，报道中的所谓纸电池，其实质就是一种锂电池，用金属锂作负极，其能量高于现在的锂离子电池，但金属锂更活泼，安全性更有问题，因此许多问题还有待进一步解决和讨论. |
14楼2008-11-13 00:00:49
用糖来听歌，索尼开发出生物电池
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http://66.196.80.202/babelfish/t ... x.html&.intl=us 中文译文： 索尼公司近日宣布开发出一种新型的生物电池，这种电池通过使用生化酶作为催化剂，将碳水化合物（糖）转换为电能输出。这种新型生物电池的基础原理，就是来源于生物将糖份转化为能量的过程。 “甜蜜”的技术 在测试中这种生物电池的电能输出可以达到50mW，已经是目前被动式生物电池的最高水平了，完全可以驱动一部Walkman进行音乐的播放。 为了实现产生世界上最高电能输出的目标，索尼开发出了一套能够分解碳水化合物来产生电能的系统，这其中包括高效的生化酶，以及能够在阳极保持生化酶火星的介质（电导材质）。 索尼还开发出一种全新的阴极结构，能够有效的为电极提供氧气，同时能够保证有足够的水容量。通过这两种技术优化的电解溶液，保证了能够达到希望的能量输出水平。 糖份是自然界中植物进行光合作用时候一种最常见的能量来源，可再生而且储量和分布都很广，可以作为未来的一种经济环保能源。 索尼计划继续开发这一系统，使之能够进一步提高能量输出的水平和时间，最终能够作为未来可实际应用的能量来源。 生物电池的原理 索尼的生物电池新技术中包括一个由糖分解酶和介质组成的阳极，一个由氧再生酶和介质组成的阴极，这两端由玻璃纸分隔开。阳极释放电子，氢离子通过下面的过程通过氧化酶的作用从葡萄糖中分解出来。 氢离子穿过隔离器向阴极移动，一旦抵达阴极氢离子和电子就和氧结合产生水。 在这一过程电化学反应当中，电子穿过外部的线路产生电能。 这种电池的详细规格如下： 酶：葡萄糖脱氢酶和硫辛酰胺脱氢酶（阳极） 胆红素氧化酶（阴极） 介质：维生素K3和和NADA抚媚（阳极） 铁氰化钾（阴极） 电极：多孔碳 电流采集：钛金属网 分割器：玻璃纸 葡萄糖：0.4M葡萄糖溶解于1.0M磷酸钠溶液中，PH值为7 最大输出：1.5 mW/cm2 (0.3V, 5 mA/cm2)，连接之后一分钟 尺寸： 39 (width) x 39 (height) x 39 (depth) mm 这种生物电池研发中的关键成果 1. 能够把酶和介质固定在电极上的技术 2. 能够高效产生氧气的阴极架构 3. 优化电解溶液来适应生物电池结构 4. 小巧的体积提供很高的能量输出 |
15楼2008-11-13 00:02:01
以色列制成低成本太阳能光电池
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造价可比传统硅光电池降低40% 记者 郑晓春 本报特拉维夫9月6日电 以色列巴依兰大学纳米技术专家研发出一种新型低成本光电池，其光电转换率与传统硅光电池相当，但造价可降低40%。 这种光电池是利用纳米技术设计的，由分布于塑料板上的海绵状微型纳米点矩阵组成，安装于导电玻璃上的金属线构成其基础部分。为了增强吸收阳光的能力，研究人员向半导体材料里注入了有机染料。 巴依兰大学纳米技术研究所主任扎班教授表示，最初他们开发的光电池板由很小的光电池矩阵组成，每个光电池片只有1平方厘米，由于光电池片比较小，片与片之间的空间多，阳光照在上面无法转换成电能，因此转换效率比较低。针对这种情况，他们将每个光电池片的面积增大到100平方厘米后，光电池矩阵捕获阳光的能力明显增强。 扎班教授称，在太阳能研发中，造价是一个重要因素。要使太阳能电池被广泛接受，必须使其生产成本低于传统的化石燃料，同时基础设施造价也要让发展中国家能够接受。他们的这项研究成果能有效地降低光电池成本，为太阳能电池占领更广阔的市场开辟了道路。此外，他也在研究减少太阳能电池中铂的使用，以进一步降低造价。 目前，耶路撒冷一家太阳能公司正与巴依兰大学合作，推进这种太阳能光电池的商业化。他们希望，今后5年能使这种光电池成功进入市场。 Source: 科技日报 |
16楼2008-11-13 00:02:48
Silicon As Smooth As Glass: Boon To Computer Chip And Solar Cell Manufacturing
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Science Daily — Without silicon there would be no computer industry since most computer chips consist of this semiconductor material. The same is true for solar cells: They too are predominantly silicon-based. -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- The monocrystals are cut in round slices approximately one millimeter thick, which experts call wafers. Their surfaces must be as smooth as glass; irregularities may only be a few nanometers wide, i.e. less than one ten thousandth of a hair. Therefore, after they have been cut out of a large silicon monocrystal, the wafers must be ground and polished. Until now, whether a surface had become sufficiently smooth was only apparent after polishing. If not, the tool had to be reattached and the process repeated – a time-consuming procedure. Moreover, the tool can easily nick the silicon when it is being attached. When that happens, the expensive material of the entire wafer must be machined until the surface is even again. Researchers at the Fraunhofer Institute for Factory Operation and Automation IFF in Magdeburg have developed a polishing tool that can constantly control the pressure on a wafer – even during polishing. Its revolutionary feature: Several piezosensors and piezoactors are integrated in the tool. If it comes across an impurity or a material defect during polishing, it intensifies the tool’s pressure on the surface of the material. The piezosensor compresses somewhat and converts this mechanical pressure into electrical voltage. This in turn signals the actor to change the tool’s pressure on the silicon and remove the uneven spot. “The primary challenge was integrating the sensors and actors in such a way that the tool’s surface is unaffected and the sensor is nevertheless close enough to the surface being machined,” says Susan Gronwald, project manager at the Fraunhofer IFF. Another advantage: The polishing tool consists of three rings lying inside one another so that a wafer’s edge can be ground with a different pressure than the inside. The new tool shortens machining time and simplifies the polishing process even for optical glass lenses. “The pressure with which material is machined could not be measured here until now,” says the expert. “Hence, the lenses had to be taken out of the polishing process again and again to inspect the surface with a laser. The final finish grinding was done manually.” The sensor-aided grinding system has been in industrial use for a short time. |
17楼2008-11-13 00:03:17
“光漏斗”比普通硅电池发电量提高3—4倍
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“光漏斗”比普通硅电池发电量提高3—4倍 科技日报2007年9月17日讯 新型数倍聚光跟踪光伏发电系统被诺贝尔奖获得者李政道称为是“理论与实践的完美结合，对中国环保事业和新能源的利用将产生深远影响”。 记者9月16日从内蒙古自治区鄂尔多斯市发改委获悉，采用该系统建设的205千瓦沙漠示范电站本月底将全部并网发电。与普遍采用的平板固定式光伏系统相比，用同样数量的硅电池，可将实际输出电量增加3—4倍，从而使我国有望依靠具有自主知识产权的新技术，解决太阳能发电受阻高成本这一世界性难题。 两年前，曾是英国剑桥大学基督圣体学院高级研究员、现为中国科技大学教授的陈应天博士回国与安徽应天新能源有限公司合作研制出新型数倍聚光跟踪光伏发电系统，两台样机已经在中国科学院理论物理所等处稳定可靠运行了一年多。该系统还被安装在上海世博会楼顶。 记者在示范电站看到，由八面体反射镜围成的聚光器或称“光漏斗”和普通光伏电池构成了一个个分立的发电单元。八面玲珑的光漏斗如钻石般在阳光下熠熠生辉。据介绍，这种新的聚光曲面和跟踪方法能更有效地接受太阳能，哪怕是阴天，单元的固定支架也可根据设定的程序实现对太阳运动的精确跟踪。与传统跟踪方式相比，新装置的可靠性和准确性大大提高，更加适于野外应用。 今年6月8日开始进行的对比实验显示，新型数倍聚光跟踪光伏发电系统的平均发电量是同面积平板固定电池的2.5—4倍，可减少70%%目前尚属高耗能、高污染的硅电池的使用。据透露，示范电站上网电价将在3元/千瓦时左右，是普通平板技术发电成本的50%%。 |
18楼2008-11-13 00:03:38
新加坡科学家研发出微生物燃料电池系统用废水发电
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新加坡科学家研发出微生物燃料电池系统用废水发电 据新加坡《联合早报》报道，废水不再是没用的废物，新加坡国大环境科学与工程系助理教授黄浩勇(35岁)研制出所需成本较低的微生物燃料电池系统，利用废水发电，不但节省能源，也非常环保。 他是本年度新加坡国家科学与科技奖青年科学家奖得主之一。 黄浩勇在国大修读土木工程系时，就对废水处理产生浓厚的兴趣。他随后修读环境工程硕士课程，到美国念博士时从事膜生物反应器研究。 他说：“废水处理是个很大的问题。另外，我也对微生物研究很有兴趣。” 他之前的研究项目包括使用纳米科技，发展新一代的正向渗透薄膜，提高净化水的产量。他目前在进行反向渗透薄膜研究，利用碳纳米管作为薄膜，让废水的水分子通过薄膜，淡化高浓度的液体。 另外，他也研制出较有效、低成本的微生物燃料电池系统，让有机废水发电。 他表示，微生物燃料电池系统虽能用废水发电，不过缺点是，电池系统内使用的钴(cobalt)过了两三个月就需要更换，若作为工业用途成本较高。 他的队伍经过一年多的研究，使微生物燃料电池系统在发电时不需要更换钴，减低成本，让这项科技更具经济效应。他解释，这项科技适用于产生许多有机废水的食品等工业。 黄浩勇目前正在为这两项研究成果申请专利权。 |
19楼2008-11-13 00:03:53
20楼2008-11-13 00:04:12
美国科学家确定单壁碳纳米管电学性质 利于电池的小型化
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【纳米科技世界快讯】 美国科学家的一项最新研究，定量测定了单壁碳纳米管(SWCNT)的电学性质。他们发现，单壁碳纳米管中每32个碳原子就能够捕获并存储一个电子，而且很容易实现受控放电。这一发现有助于科学家按照需求设计出作为电容器的碳纳米管，并提高电子设备和太阳能电池的光电和电气化学性能。相关论文发表在美国化学学会的新创刊物ACS Nano杂志上。 进行该项研究的是圣母大学的Anusorn Kongkanand和Prashant Kamat，他们监控了由二氧化钛半导体颗粒和单壁碳纳米管组成的复合系统，在达到电荷平衡的过程中电子的转移。 当二氧化钛纳米颗粒受到紫外光激发时，它的电子会发生分离，其中的一些由于受到限制而不能自由移动，每12纳米长的二氧化钛颗粒中大约有3770个电子是这种情况。这些受限制的电子会呈现出蓝色。然而，当研究人员将二氧化钛颗粒和单壁碳纳米管形成系统时，蓝色减弱了，这是由于一些封存于二氧化钛中的电子转移到了单壁碳纳米管。研究人员发现，当单壁碳纳米管的浓度达到100mg/L时，蓝色彻底消失，这说明二氧化钛中的封存电子完全转移到了单壁碳纳米管。 计算表明，单壁碳纳米管中每32个碳原子就能够捕获并存储一个电子，整个过程在亿分之一秒内完成。如此之高的电子存储能力使碳纳米管变成一个“超级电容器”。 论文作者Kamat表示：“利用碳纳米管所占空间小的特点来提升电子的存储能力，对于电池的小型化至关重要。”Kamat强调，只有当半导体颗粒和碳纳米管二者的费米能达到平衡，电子转移才会停止，因此，32个碳原子捕获一个电子是受到系统能量限制的保守估计。这也就意味着如果改变半导体材料或者改变充电方法，单壁碳纳米管有可能存储更多的电子。同时，半导体的能量级别越高，转移的电子也会越多。 为了实现放电，研究人员在系统中加入可接收电子的硫堇，其还原电势比碳纳米管更高，因此电子会从碳纳米管中流入硫堇。 研究人员表示：“单壁碳纳米管接收和转移电子的能力凸显了它在电子转移过程中的中介作用。单壁碳纳米管的充放电特性将在提升光电转化方面起到重要作用。” |
21楼2008-11-13 00:05:04
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Carbon nanotubes' electronic properties optimized for future applications While researching the unique electrical properties of single-walled carbon nanotubes (SWCNTs), researchers have demonstrated the nanotubes’ ability to capture and store one electron per 32 carbon atoms in a SWCNT. The stored electrons can be readily discharged on demand with the addition of an electron-accepting dye, significantly increasing the photocurrent and photoconductivity of electrical systems. University of Notre Dame scientists Anusorn Kongkanand and Prashant Kamat monitored the transfer of electrons from semiconductor particles to SWCNTs as the composite system strained to achieve charge equilibrium. The study, published in ACS Nano, will be useful for the design of nanotubes as a way to direct the flow charge and boost photoelectrochemical performance for applications including electronic devices and solar cells. “Although the electron storage property of carbon nanotubes is well known, there is no convenient or simple way to make a quantitative estimate of storage capacity,” Kamat told PhysOrg.com. “Our study provides a quantitative measure of the number of electrons stored in carbon nanotubes and its ability to discharge them on demand. In addition, one can use the information to estimate the Fermi level of the semiconductor-carbon nanotube composite—an important parameter in evaluating the performance of SWCNT devices for electronic and photovoltaic applications.” When excited by a UV laser, titanium dioxide nanoparticles undergo charge separation, where some of the semiconductor’s electrons get trapped—an estimated 3,770 electrons per 12-nm-long nanoparticle. Electrons trapped in the titanium dioxide displayed a blue coloration (a 650-nm absorption band). But when the researchers introduced SWCNTs to the titanium dioxide particles, the blue color decreased. Because SWCNTs don’t have any detectable absorption in the visible range, this lack of color meant that some of the electrons trapped in the titanium dioxide were transferred to the SWCNTs. “The transfer of electrons represents charge equilibration between the two semiconductor systems having different Fermi levels,” the scientists explained. “At a concentration of 100 mg/L SWCNT, we observe complete disappearance of the 650 nm absorption band, thus indicating complete transfer of electrons to SWCNT.” Complete transfer consisted of 1 electron per 32 atoms of carbon atoms (building blocks of the SWCNTs), and occurred in just 10 nanoseconds. Such a high electron capacity turned the SWCNTs into supercapacitors, which can be useful in electronics applications. “Boosting the electron storage in a tiny volume occupied by carbon nanotubes should be attractive for miniaturizing storage batteries,” Kamat said. “The electron transfer from semiconductor to the carbon nanotubes continues until the Fermi energies of the two match or equilibrate. Therefore, the estimate of the 32 electrons per carbon atom is limited by the energetics of the photoirradiated titanium dioxide system. “By selecting another semiconductor particle with a more negative conduction band than that of TiO2 (in other words using a more energetically favorable semiconductor) or alternate charging methods (such as electrical or electrochemical charging), it should be possible to store more electrons,” Kamat explained. “The higher the energy level of the semiconductor, the greater the number of electrons transferred.” Then to discharge the electrons, the researchers added thionine, a dye that acts as an electron acceptor. Electrons from the SWCNTs transferred to the thionine, which has a reduction potential that is more positive than the SWCNTs, causing charge equilibration to drive the electrons out of the nanotubes. “The ability of SWCNTs to accept electrons and transfer them to a suitable electron acceptor highlights the mediating role of these nanotubes in a charge transfer process,” the researchers concluded. “This electron-charging and -discharging property of SWCNT will play an important role in improving the performance of light energy harvesting applications.” Citation: Kongkanand, Anusorn, and Kamat, Prashant V. “Electron Storage in Single Wall Carbon Nanotubes. Fermi Level Equilibration in Semiconductor-SWCNT Suspensions.” ACS Nano, Vol. 1, No.1, 13-21, 2007. Source: PhysOrg.com |
22楼2008-11-13 00:05:20
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太阳能大碟技术白天晚上都发电 记者 唐婷 本报讯 “我们研发的太阳能大碟集热技术和其他类型太阳能集热技术相比，热电转换效率更高，而且其大规模生产成本更低，这一技术代表着太阳能集热技术发展的趋势。”日前，来北京参加2007年世界太阳能大会的澳大利亚国立大学工程学院太阳能研究中心首席科学家KeithLovegrove博士对记者表示。 据KeithLovegrove博士介绍，他所领导的科研团队已经在太阳能集热技术领域从事了30多年的研究，大碟技术是他们研究的主要成果。在他们的实验室里有一个世界上最大的利用光热发电的大碟，该碟表面面积有400平方米。大碟通过吸收光能，将流入的液态水变成水蒸气，再由水蒸气驱动发动机产生电能。其整个能量转换过程就是先将光能转换成热能，再将热能转换为电能，实现热电转换效率为19.14%%。目前，世界上另两种主要的太阳能集热技术，即槽型和塔型太阳能集热技术，热电转换效率分别为10.59%%和13.81%%。 对于该技术夜晚是否可以工作的问题，KeithLovegrove博士告诉记者，他们研发的一项电能存储技术可以使大碟晚上也能发电。他说，这项技术可以将白天吸收的光能所产生的热能通过化学反应转化成气体和液体存储起来，晚上再将其还原成热能来发电。该技术目前是世界首创，已被澳大利亚环保遗产部国际气候变化司列为重点发展技术项目。 From：科技日报 |
23楼2008-11-13 00:05:31
韩国开发出氢燃料高能电池 未来可做手机电源
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腾讯科技2007年10月11日讯 据国外媒体报道，韩国近日开发出一种氢燃料高能电池，并成功用于无人飞机。目前美军使用的无人侦察机一次飞行能持续40至60分钟，而使用这种氢燃料高能电池能使飞行时间提高十倍，达到10个小时。韩国研究人员称：“氢燃料高能电池在无人飞机上使用成功，有望推广至数码相机和机器人等产品上为其提供动力。” 韩国科学技术院（KAIST）航空工程学权世震教授和沈炫哲教授领导的研究小组开发出了这种氢燃料高能电池，10月9日，他们将这种电池用于无人飞机并进行长时间飞行实验获得成功。 水在电的作用下会分解出氢和氧原子。氢燃料电池正是反向利用这一原理，利用氢原素和空气中的氧原素发生反应产生电能。美国海军研究所和佐治亚州工学院在2006年联合开发出了使用压缩氢气燃料的电池并用于无人飞机。 权世震教授说：“燃料使用了硼氢化钠，因为是液体，它能比气体状态的压缩氢气产生更多的氢，也降低了意外火灾的风险，更便于推向市场。同时，这种氢燃料高能电池比普通电池能产生10倍以上的电能，有望推广到数码相机手机等电子产品。” 此次公开的使用氢燃料高能电池的飞机重2千克（其中氢燃料电池重750克），长1.2米，宽0.7米，同美军无人侦察机大小相当。据称，如果将氢燃料电池重量降至500克，无人飞机也有可能飞行10小时。 |
24楼2008-11-13 00:06:04
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Facets for fuel cells Platinum nanostructures on alumina become highly faceted at temperatures greater than 700 °C, making them potentially useful for high-temperature fuel-cell catalyst applications. The new, simple self-assembly technique to make such metal-oxide systems is simpler than existing chemical methods, says Deeder Aurongzeb of Texas Tech University in the US. Self-assembly is an attractive technique for producing nanoscale structures because it is relatively simple compared with conventional patterning techniques, such as focused ion beam, lithography or template nanoimprinting. Although planar platinum is already widely used in fuel-cell applications, faceted platinum nanoclusters should be even more efficient catalysts. However, little is known about how stable such nanostructures are and how they form. Clusters forming Aurongzeb has now grown faceted platinum nanodots in alumina by rapidly heating platinum thin-films to 700 °C. He found that at a critical film thickness of 2 nm, the clusters form facets with multifaceted sidewalls. These structures greatly increase the surface area of the material, so increasing efficiency. According to Aurongzeb, the shape of the nanoclusters can be controlled with temperature and time. "It is interesting to see a cubic close-packed metal turn into various geometric shapes, such as hexagonal, pentagonal and triangular, at high temperatures," he told nanotechweb.org. "These structures are very stable, thus useful for high-temperature applications." Deeder Aurongzeb The rapid annealing technique could be extended to other metal-oxide systems. Applications include gas sensing and catalytic decomposition of environmentally unfriendly material, says Aurongzeb. The experiment itself is "really simple", he adds. "Metal diffuses inside an oxide if you heat the combination to a very high temperature, so the trick is to find the right film thickness and temperature where the atomic self-diffusion is faster than the diffusion of atoms in the host. This is achieved by rapid thermal annealing of films at various film thicknesses and temperatures to find the exact point at which this happens." High-temperature, long-life fuel cells use oxide surfaces like alumina to support platinum. However, the problem is that there are few reaction sites available on the surface of the platinum. "Crystal facets are sources for reaction sites and they are tightly bonded" explained Aurongzeb "and we showed that up to 18 facets/steps can be formed on the platinum nanodots." He goes on to say that it is very difficult to fabricate platinum with such a large number of facets using conventional chemical methods that have much less control. Aurongzeb now plans to nanoalloy and layer the nanodots with other metals like osmium, iridium and conducting oxides and oxinitrides to form even higher numbers of facets and reaction sites. "I believe more-complex combinations with other supports like carbon or carbides will lead to very interesting shapes and sizes that will be stable at high temperatures," he said. "Not to mention the interesting physics that will unfold with all of these studies." The work was published in J. Appl. Phys. Source：nanotechweb.org |
25楼2008-11-13 00:07:07
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Light-harvesting nanowire could drive tiny devices A nanowire that harvests enough electricity from light to power a nanoscale circuit has been demonstrated by US researchers. The nanowire, which resembles a miniscule coaxial cable, is made of layers of silicon and is the first example of a self-contained nanoscale solar cell. Several research groups are using nanoscale components and materials to improve solar cells. But none has yet managed to develop anything with efficiency rivalling existing solar cells, which convert between 20 and 25% of sunlight into electricity. These research projects also mostly involve combining nanoscale elements, such as nano-particles, with larger components, notes Charles Lieber of Harvard University, who led the study. Lieber's new nanowire functions as a complete solar cell. At its core is a rod-shaped crystal of silicon, about 100 nanometres across, doped with boron. Layers of polycrystalline silicon are added to wrap it in a 50-nm-thick layer of undoped silicon and a 50-nm-thick outer coating of silicon doped with phosphorus. Proof of concept As light hits the wire, electrons are knocked loose from the silicon crystal, leaving positively charged "holes" that can also move through the material. The electrons tend to move towards the outer layer of the nanowire, while the holes move towards its core, with the layer between keeping the two separate. The flow of electrons and holes creates an electric current when the nanowire is connected to a circuit. Although the proof-of-concept device only converts about 3% of light into electricity, Liever says it "allows us to study a fundamentally different geometry for photovoltaic cells, which may be attractive for improving the efficiency." Purer crystal He also believes it may be possible to boost the nanowire's efficiency by getting rid of defects in the crystal. "Our goal is to get in the 15% [efficiency] range," Lieber says." But the most immediate promise for the nanowires, in Lieber's view, is as power sources for nanoscale electronics. The study showed that an individual nanowire can create about 50 to 200 picowatts of electricity from sunlight – enough to power a tiny circuit. "The idea of using single photovoltaic nano-structure to power a neighbouring nano-electric unit is really elegant," says Peidong Yang of the University of California at Berkeley, who was not involved with the work. However, Yang adds that "it is still unclear whether these devices would outperform more traditional silicon solar cells." Journal reference: Nature (DOI:10.1038/nature06181 |
26楼2008-11-13 00:07:52
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科学家从蛾和蝉身上找到改善太阳能电池性能的灵感 From moths and cicadas come improvements to solar cells Stanley Chih-Hung Sun (left), a University of Florida chemical engineering doctoral student, and Peng Jiang, an assistant professor of chemical engineering, take images of a moth eye with a powerful scanning electron microscope. The researchers are mimicking the microscopic structure of moth eyes and cicada wings to create new anti-reflective and water-repellant coatings. These coatings could make solar cells both more efficient and self-cleaning, and they may also lead to more transparent windows, more legible computer screens and other improvements to consumer products. Photo by Ray Carson/University of Florida Designing better solar cells might seem a question of electronics or chemistry, but for one University of Florida engineer, it starts with bugs. Peng Jiang, an assistant professor of chemical engineering, is drawing inspiration from the eyes of moths and the wings of cicadas to create unusual new anti-reflective and water-repellant coatings — coatings that appear to have potential to make solar cells both more efficient and self-cleaning. Windows in cars and homes, computer screens and other consumer products also could improve thanks to the super-transparent coatings. “Nature is an amazing innovator,” Jiang said. “What I’m interested in doing is mimicking the structure of some remarkable biological systems for real-world use.” Jiang’s research, most recently reported in a September paper in the journal Applied Physics Letters, focuses on a new technique to manufacture a coating whose microscopic structure closely resembles that of moth eyes. Most moth eyes are made up of adjacent hexagonal sectors. Each sector is filled with thousands of orderly rows of miniscule bumps, or nipple-like protrusions. Though formed so perfectly they appear almost manufactured, each protrusion measures less than 300 nanometers, or 300 billionths of a meter — a size that renders them invisible to all but the most powerful electron microscopes. When moths encounter light, these orderly arrays of protrusions interfere with its transmission and reflection, rendering the light all but invisible. Biologists believe this trait evolved in moths, which are often nocturnal, because it prevents their eyes from reflecting moon or starlight, which would make them easier targets for predators. Jiang said engineers have sought to replicate the eyes’ microscopic structure using a printing technique called lithography, but it is expensive and ill-suited to creating the extremely tiny rows of protrusions that make the moth eyes so effective. To get around this problem, Jiang developed a non-lithographic technique, called spin coating. Unlike lithography, which attempts to carve out the nipple-like pattern on the target surface, spin coating seeks to build the pattern up from scratch on the target. Jiang places a liquid suspension of nanoparticles on a circular silicon wafer, such as that used in photovoltaic cells. A motor spins the wafer, with centrifugal force distributing the liquid. When it dries, it leaves behind the ordered particles in place. The Applied Physics Letters paper reports that Jiang successfully used this comparatively low-tech technique to create a moth eye-like anti-reflective coating on glass and plastic substrates. But the researcher said he has since gone further, applying the same technique to silicon wafer surfaces to add a unique property of cicada wings. Cicada wings are amazingly effective at rapidly shedding water and dirt, apparently because the insects often need to fly in humid environments, Jiang said. At the particle level, the wings have a structure very similar to that of the moth eyes — except that rather than deflecting light, tiny pockets of air around each nipple-like protrusion buoy water droplets. Jiang said he and his two doctoral students, Chih-Hung Sun and Nicholas Linn, as well as a collaborator, Professor Bin Jiang at Portland State University in Oregon, have now replicated this structure using the spin coating process, also on a silicon wafer. He demonstrated the achievement in his laboratory, placing a drop of water on a postage stamp-sized wafer coated with the cicada wing-like coating. As if electrified, the drop danced across the surface of the wafer until it reached the edge. His research could have a number of applications, Jiang said. The anti-reflective coating may improve the performance of solar cells because it would increase the amount of light the cells receive, he said. Current production coatings reflect more than 10 percent of the light at certain wavelengths, whereas Jiang says his coating reflects less than 2 percent at those wavelengths. The water-repelling element would be useful for keeping the cells clean – a necessity because dirt or dust easily dulls their performance. Rain or simply hosing the coated cells down would clean them adequately, he said. Jiang added the coatings could also improve the performance of ordinary windows on cars or homes, increasing visibility and reducing the need for cleaning. That said, numerous challenges remain, including learning how to “scale up” the spin coating process so that it could be used for industrial production, he said. Yadong Yin, an assistant chemistry professor at the University of California, Riverside, said Jiang’s research is important in part because it suggests that there is a low-cost alternative to current anti-reflection production techniques. “Importantly,” he said, “the low cost in this case did not lead to low performance.” Source: UF |
27楼2008-11-13 00:09:07
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A better catalyst for fuel cells? 30 October 2007 Alloy nanoparticles that efficiently catalyse oxygen's conversion into water - the energy-releasing reaction that occurs in fuel cells - have been discovered by Peter Strasser and colleagues at the University of Houston, US. The particles are up to six times more active than pure platinum, the material typically used in current fuel cells. Stresser initially examined particles combining platinum and copper, which were subjected to an electrochemical dealloying process to remove copper from the particle surface. The resulting catalyst has a platinum-rich outer shell - where the reaction takes place - combined with a copper-enriched core. 'We were investigating different catalyst stoichiometries, and noticed alloys with over 50 per cent copper had high activity,' Stresser told Chemistry World. 'We were sure these catalysts couldn't be stable - that the copper had to be leaching away during the electrochemical reaction. But leaching away the surface copper is exactly what gives you the high activity, so we turned this into a synthetic strategy.' Simply making an alloy of 80 per cent platinum and 20 per cent copper gives a catalyst little better than pure platinum, said Stresser. But making an alloy of the same proportions by dealloying a copper-rich precursor produces a much more active catalyst. 'The corrosion process activates the catalyst, because there's some base metal in the core, but a platinum-rich shell.' Elevated Activity Stresser attributes the enhanced reactivity to slightly shorter distances between neighbouring platinum atoms in the particle shell, a geometric difference that stems from the copper atoms in the core. 'Shorter platinum-platinum distances change the metal's electronic structure, which changes the strength of the bond that forms between platinum and oxygen [during catalysis]. And we know catalytic activity is all about bond strength.' 'We plan to corroborate, or correct, the hypothesis by collaboration with the Stanford Cyclotron to see if the platinum-platinum distance really is smaller,' Stresser added. 'Also, the durability of our catalysts is unclear, and requires more work to understand how stable it would be over the lifetime of a fuel cell.' Nanoparticles combining platinum (white) and copper (pink) were subjected to an electrochemical dealloying process to remove copper from the particle surface. © by Peter Strasser The Houston team has also extended the technique to turnery mixtures that include cobalt as well as platinum and copper, which similarly were four to five times more active than pure platinum. But Frank DiSalvo, who works on nanoparticular electrocatalysts at the Cornell Fuel Cell Institute, US, told Chemistry World that catalysts with 10-100 times better activity are needed. 'A third of the fuel cell's energy is currently lost driving this reaction,' he said. 'To make a big advance you really need an electrode more like two to three orders of magnitude more active.' James Mitchell Crow ReferencesS Koh and P Strasser, J. Am. Chem. Soc., 2007 (DOI: 10.1021/ja0742784) Source Chemistry World. [ Last edited by feynman on 2008-11-13 at 00:13 ] |
28楼2008-11-13 00:09:33
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英国开发出笔记本电脑燃料电池 作者：群芳 来源：科学时报(http://www.sciencenet.cn/) 发布时间：2007-11-5 6:23:22 小号字 中号字 大号字 英国科学家日前成功研制出新一代燃料电池，有望代替笔记本电脑上的充电电池。 不久的将来，也许笔记本电脑用户再也不用关掉电脑为电池充电了。新燃料电池的能源来自于一节小小的甲醇燃料电池，当电量用完时，用户只需要将另一块电池插入电池组的凹槽处即可，就像为笔更换笔芯一样简单。 据英国媒体报道，由位于英国剑桥的CMR燃料电池公司开发的高性能紧凑型燃料电池，将替代笔记本电脑上的充电电池。 燃料电池时代大约开始于1839年英国科学家William Grove发表的一篇介绍铂选择催化氢氧燃料电池的论文，但直到20世纪60年代，这一理念才被运用于实践。迄今为止，燃料电池所面临的主要挑战是成本高、性能低。由于贵金属材料用做催化剂，燃料电池的费用比传统发动机的运行成本昂贵，并且产生的能力密度也相对较低。 如何开发出一种性能更高、体积更小的燃料电池，CMR技术总监Michael Priestnall设想，如果能找到一种替代传统铂催化剂的物质作用于燃料电池的两极，也就意味着空气和燃料混合的新型电池组有可能诞生。 与电池的相似之处是，燃料电池会产生恒定电流。不同之处在于，它们通过外部的燃料供应（阳极）和氧化剂（阴极）来产生电流。这是一个在催化剂作用下产生电化学反应的过程。其工作原理是，通过反应物的导入和生成物的导出，直接将化学能源转化成高效能的电流。燃料电池实际上就是将持续的化学能转变为持续的电流。高效能、无噪音、低排放是这一技术最为突出的几大优点。 目前，这种比传统燃料电池或现在的锂离子蓄电池体积更小、质量更轻的廉价且高效能的燃料电池即将走向应用，该技术有望应用于韩国和日本大型个人电脑和笔记本制造商的产品。 |
29楼2008-11-13 00:14:20
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22 November 2007 A team of Italian scientists has created a sunlight-powered cell that produces pure hydrogen from water. The team from the University of Milan and the University of Pavia are studying environmentally friendly ways to generate hydrogen, which could in future replace fossil fuels as a major energy source. The new cell has two compartments filled with water and separated by an electrode made of platinum and titanium dioxide. When it is illuminated, by sunlight or an ordinary lamp, the electrode catalyses the splitting of the water into hydrogen and oxygen gas. "The new design of cell keeps the production of hydrogen and oxygen separate" Elena Selli, who led the research, pointed out 'Almost all the photocatalytic water splitting systems described so far imply the evolution of a mixture of hydrogen and oxygen in only one reactor; of course, a separation step would be required prior to any use of hydrogen.' The new design of cell keeps the production of the two gases separate, resulting in streams of hydrogen and oxygen that do not need any purification to be useful. 'Our results demonstrate that hydrogen production from water photocatalytic splitting should be regarded as a practically viable, extremely promising way for clean, low cost and environmentally friendly conversion of solar energy into chemical energy,' said Selli. The team is working on improving the efficiency of the cell by making the titanium dioxide layer of the electrode more sensitive to visible light. Clare Boothby Link to journal article A photocatalytic water splitting device for separate hydrogen and oxygen evolution Elena Selli, Gian Luca Chiarello, Eliana Quartarone, Piercarlo Mustarelli, Ilenia Rossetti and Lucio Forni, Chem. Commun., 2007 DOI: 10.1039/b711747g Source: Chemistry World. |
30楼2008-11-13 00:15:30
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Experiments reveal unexpected activity of fuel cell catalysts A scanning tunneling microscopy (STM) image taken of ceria nanoparticles on a gold surface. Size: 40 x 40 nanometers. Credit: Brookhaven National Laboratory Researchers at the U.S. Department of Energy’s Brookhaven National Laboratory have unveiled important details about a class of catalysts that could help improve the performance of fuel cells. With the goal of producing “clean” hydrogen for fuel cell reactions in mind, the researchers determined why two next-generation catalysts including gold, cerium, titanium, and oxygen nanomaterials exhibit very high activity. Their results will be published online in the December 14, 2007, edition of the journal Science. Fuel cells combine hydrogen and oxygen without combustion to produce direct electrical power and water. They are attractive as a source of power for transportation applications because of their high energy efficiency, the potential for using a variety of fuel sources, and their zero emissions. However, a major problem facing this technology is that the hydrogen-rich materials feeding the reaction often contain carbon monoxide (CO), which is formed during hydrogen production. Within a fuel cell, CO “poisons” the expensive platinum-based catalysts that convert hydrogen into electricity, deteriorating their efficiency over time and requiring their replacement. “Fuel cell reactions are very demanding processes that require very pure hydrogen,” said Brookhaven chemist Jose Rodriguez. “You need to find some way to eliminate the impurities, and that’s where the water-gas shift reaction comes into play.” The “water-gas shift” (WGS) reaction combines CO with water to produce additional hydrogen gas and carbon dioxide. With the assistance of proper catalysts, this process can convert nearly 100 percent of the CO into carbon dioxide. Rodriguez’s group, which includes researchers from Brookhaven’s chemistry department, the Center for Functional Nanomaterials (CFN), and the Central University of Venezuela, studied two “next-generation” WGS nanoscale catalysts: gold-cerium oxide and gold-titanium oxide. “These nanomaterials have recently been reported as very efficient catalysts for the WGS reaction,” said Brookhaven chemist Jan Hrbek. “This was a surprising finding because neither bulk gold nor bulk ceria and titania are active as catalysts.” To determine how these nanocatalysts work, the research team developed so-called “inverse model catalysts.” The WGS catalysts usually consist of gold nanoparticles dispersed on a ceria or titania surface – a small amount of the expensive metal placed on the inexpensive oxide. But to get a better look at the surface interactions, the researchers placed ceria or titania nanoparticles on a pure gold surface. “For the first time, we established that although pure gold is inert for the WGS reaction, if you put a small amount of ceria or titanium on it, it becomes extremely active,” Rodriguez said. “So although these inverse catalysts are just models, they have catalytic activity comparable to, and sometimes better than, the real deal.” Using a technique called x-ray photoelectron spectroscopy at Brookhaven’s National Synchrotron Light Source, as well as scanning tunneling microscopy and calculations, the researchers discovered that the catalysts’ oxides are the reason for their high activity. “The oxides have unique properties on the nanoscale and are able to break apart water molecules, which is the most difficult part of the WGS reaction,” Hrbek said. Added Brookhaven physicist Ping Liu: “After you dissociate the water, the reaction continues on to eliminate CO. But if you don’t have nanosized oxide particles, none of this will work.” Source: Brookhaven National Laboratory, by Kendra Snyder |
31楼2008-11-13 00:16:58
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以色列研制出纳米染料太阳能电池 作者：郑晓春 来源：科技日报 发布时间：2007-12-29 以色列奥莱恩太阳能公司与巴依兰大学合作开发出一种纳米染料太阳能电池。该电池的关键部分是只有10纳米的氧化钛，当阳光照射到覆有染料涂层的氧化钛粒子后，它会像自然界的光合作用那样，利用有机染料吸收光和传递太阳能，并通过氧化钛导带将太阳能转换为电流。 该公司负责人布莱恩称，这种太阳能电池的特点是效率较高、造价低。由于染料技术在早晚光线较暗的条件下也能发电，此外，他们还使用了巴依兰大学先进材料与纳米技术中心主任扎班教授发明的将纳米电池连成大的单一太阳能电池的新方法和奥莱恩公司的染料电池技术，因此，这种太阳能电池具有较高的光电效率。 另外，太阳能发电要取得成功，降低造价是一个重要因素，不仅发电成本要低于目前的化石燃料发电，同时还要大大降低基础建设费用，否则许多国家特别是发展中国家的消费者只能“望洋兴叹”。现在的硅太阳能电池技术虽比较成熟，但价格一直居高不下，而他们研发的这种染料太阳能电池的发电成本只有硅太阳能电池的一半，生产线投入也只是硅太阳能电池的一小部分，因而具有较好的市场前景。 布莱恩表示，该产品明年有望实现商品化，他们的最初目标不是与电力公司竞争，而是向私人电力公司不愿染指的亚、非、拉等发展中国家中尚未通电的边远地区家庭提供服务，这是一个巨大的市场。他相信，他们研发的可为照明和小家电提供足够电力的染料太阳能电池在这些地区会有用武之地。 科学网 |
32楼2008-11-13 00:17:18
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新纳米薄膜展现高效转换太阳能前景 在一场让太阳能电池更廉价和更高效的竞赛中，许多科学家和起步阶段的公司正在把希望放在利用纳米结构的新设计上。纳米结构材料是在十亿分之一米的尺度上制造的材料。利用纳米技术，科学家可以测试和控制一种材料如何产生、捕捉、转移和贮存自由电子——这些属性对于把阳光转换成电能非常重要。 两种制造太阳能电池材料的纳米技术方法已经显示出了特别的前景。一种方法使用金属氧化物纳米颗粒（例如二氧化钛）薄膜，掺入氮等其他元素。另一种策略利用可以强烈地吸收可见光的量子点——一类纳米尺寸的晶体。这些微小的半导体把电子注入到金属氧化物薄膜中，或者说把它“敏化”，从而增强太阳能转换。掺杂和量子点敏化都增强了金属氧化物材料对可见光的吸收。 加州大学圣克鲁兹分校的化学教授张金中说，把这两种方法结合起来看来可以比单独使用任何一种方法产生更好的太阳能电池材料。张金中领导的一个来自加州、墨西哥和中国的研究组制造出了一种掺氮并用量子点敏化的薄膜。在测试中，这种新的纳米复合材料的性能比预期的更好——似乎整个材料的功能大于两种单独成分之和。 “我们发现了一种新的策略，它可能对增强基于纳米材料的太阳能电池的光响应和转换效率非常有用，”张金中说。 “我们起初以为我们能实现的最好结果是达到两者之和，而且倘若我们没有弄对，我们可能得到更糟糕的结果。但是令人吃惊的是，这些材料远远更好。” 该研究组的发现于1月4日以论文的形式发表在了《物理化学杂志C》的网站上。该论文的第一作者是TzararaLopez-Luke，她是张金中实验室的访问研究生，如今在墨西哥莫雷利亚的Metalurgicas研究所（Instituto deInvestigaciones Metalurgicas, UMSNH）。 张金中的研究组用一大批工具描绘了这种新的纳米复合材料的特性，这包括原子力显微镜（AFM）、透射电子显微镜（TEM），拉曼光谱仪和光电化学技术。他们制备的膜的厚度在150纳米到1100纳米之间，二氧化钛粒子的平均尺寸是100纳米。他们用氮原子掺杂了二氧化钛晶格。他们把硒化镉制成的量子点用化学方式连接在了这种薄膜上，用于敏化。 制造出的复合材料提供了优势的联合。氮掺杂可以让这种材料吸收广泛的光能，包括电磁波谱中的可见光区域。量子点还能增强可见光吸收，并增加光电流和这种材料的能量转换。 这个研究组报告说，与仅掺杂了氮或者仅嵌入了硒化镉量子点的材料相比，这种纳米复合材料表现出了更高的“光电转化效率（IPCE）”的性能。张金中说，这种纳米复合材料的IPCE是其他两种材料的IPCE之和的3倍。 “我们认为原因在于电荷更容易在这种材料中跳跃，”他解释说。“只有在同时拥有量子点敏化和氮掺杂的情况下才会发生这种情况。” 这种纳米复合材料不仅可以用于增强光电池，还可以作为其他能源技术的一部分。张金中的长期目标之一就是让高效的太阳能电池与最先进的光电化学电池相结合。这样一种装置在理论上可能利用阳光产生的能量把水分解，从而生产出氢燃料（见早先的一份新闻稿http://press.ucsc.edu/text.asp?pid=712）。这种纳米复合材料还可能有潜力用于把二氧化碳转化为碳氢燃料（例如甲烷）的装置。 这种制造太阳能电池材料的新策略为张金中的实验室提供了一条有前途的道路，在未来数年加以探索。 “我感到非常激动，因为这一研究是初步的，而且我们现在可以进行很多的优化，”张金中指出。“我们有三种材料——或者三种参数——可供调整，从而达到正确的能级。” 在本质上，这个研究组正在设法操纵材料，当阳光照在它们的上面的时候，从而让产生的自由电子可以轻易地从一个能级运动到另一个能级——或者在不同的材料间跳跃——并高效地转化成电流。 “我们正在研究的在本质上是‘能隙工程学’。我们操纵纳米复合材料的能级，从而让电子可以更高效地形成电流，“张金中说。“如果我们的模型是正确的，我们就为这类策略提供了一个好的例子。”（来源：EurekAlert!中文版） （《物理化学杂志C》（Journal of Physical Chemistry C），10.1021/jp077345p S1932-7447(07)07345-1，Tzarara López-Luke, Jin Z. Zhang） 更多阅读（英文） 《物理化学杂志C》论文摘要 http://www.sciencenet.cn/htmlpaper/20081912553477730.html |
33楼2008-11-13 00:17:40
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JRSE：新型微型太阳能电池研制成功 论文作者：Xiaomei Jiang 期刊：JRSE 发布时间：2008-11-10 16:59:48 新型微型太阳能电池研制成功 迄今最小的太阳能电池作为更小型微型机器的电源已经成功地通过了测试。发表在美国物理联合会（AIP）出版的《可再生与可持续能源杂志》（JRSE）创刊号上的一篇文章描述了20个这样的电池组成的1英寸长的阵列——每一个电池大约只有标准的12磅字体的小写字母“o”尺寸的 1/4。 南佛罗里达大学的Xiaomei Jiang领导了这项研究，她说这些电池是用一种有机聚合物制成的，在一项旨在证明它们有能力为检测化学物质泄漏和其他用途的微型设备供电的实验中，这些电池被连接在了一起。 传统的太阳能电池——例如安装在屋顶的商品化太阳能电池——使用一种脆弱的硅层，计算机芯片也使用这种物质制成。相比之下，有机太阳能电池依靠的是一种聚合物，它具有和硅片一样的电性能，但是可以溶解并印刷在柔性材料上。 Jiang说：“我认为这些材料比传统的硅材料拥有更多的潜力，它们可以喷涂在暴露于阳光下的任何表面——一件制服、一辆汽车或一幢房屋。” Jiang 和她的同事制造出了20个微型太阳能电池组成的阵列，为一个用于探测危险化学物质和毒物的微型传感器供电。这个探测器被称为微机电系统（MEMS）设备，它是用碳纳米管制成的，而且已经用普通的电池供电的直流电源进行了测试。为它提供足够的能量并接入一个电路，通过测量化学物质进入碳纳米管的时候出现的电信号变化，这些碳纳米管可以灵敏地探测到特定的化学物质。化学物质的类型可以通过电信号的精密变化区别开。 该设备需要一个15伏的电源才能工作，而Jiang的太阳能电池阵列目前在其实验室测试中可以提供大约一半电压，也就是最多7.8伏。她说，下一步就是对这种设备进行优化，从而增加电压，然后把这种缩微太阳能电池阵列与碳纳米管化学物质传感器结合在一起。Jiang估计到今年底，他们将有能力让他们的下一代太阳能电池阵列达到这种的供电水平。 Xiaomei Jiang撰写的论文"Fabrication of organic solar array for applications in microelectromechanical systems"将于2008年11月6日发表在《可再生与可持续能源杂志》上。（来源：EurekAlert!中文版） （《可再生与可持续能源杂志》（JRSE），DOI: 10.1063/1.2998825 ，Jason Lewis，Xiaomei Jiang） 更多阅读（英文） 《可再生与可持续能源杂志》发表论文摘要 科学网 |
34楼2008-11-13 00:18:58
Hot Article: New Micro Fuel Cell
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15 July 2008 Siu Ming Kwan and King Lun Yeung from the Hong Kong University of Science and Technology have made an inorganic zeolite proton-exchange micromembrane and assembled it into a workable micro fuel cell. Yeung explains that this is the first time that a nanoporous zeolite membrane has been studied as a proton-exchange membrane for hydrogen fuel cells. They discovered that their microfabricated HZSM-5 micromembrane achieved performance on a par with a commercial membrane, Nafion 117. They believe their work shows remarkable progress in inorganic proton conducting membranes, as sufficient proton conductivity is currently only achieved at significantly higher temperatures. 'The zeolite micromembrane could offer greater avenues for designing more efficient micro fuel cells either based on hydrogen or liquid hydrocarbon fuels,' predicts Yeung. Rachel Cooper Link to journal articleZeolite micro fuel cell Siu Ming Kwan and King Lun Yeung, Chem. Commun., 2008 DOI: 10.1039/b809019j |
35楼2008-11-13 00:20:18
Driving power for electric cars
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Scientists have made the first renewable fuel cell that can store more energy than petrol. Electric vehicles are potentially more environmentally friendly than petrol vehicles because they do not emit greenhouse gases, but the cells they use for power can't store as much energy as fossil fuels. Now, Stuart Licht and colleagues at the University of Massachusetts, Boston, US, have developed a vanadium boride-air fuel cell with a much larger energy capacity than current vehicle batteries. 'The cell has ten times the energy capacity of lithium ion batteries and three times the energy density of zinc-air batteries,' says Licht, 'although all these devices work in the same way.' General Motors' electric car 'Volt' © General Motors In its electric car 'Volt', launching in 2010, General Motors (GM) uses a lithium ion battery which can power the car for 40 miles before it needs to be recharged. To extend this range, GM added a standard combustion engine to recharge the battery when it runs low. "Our renewable fuel cell opens the door to electric vehicles with viable driving ranges, without a separate combustion engine and frequent battery recharges" - Stuart Licht, University of Massachusetts, US 'Our renewable fuel cell opens the door to electric vehicles with viable driving ranges, without a separate combustion engine and frequent battery recharges,' says Licht. The vanadium boride-air fuel cell needs only air and fresh fuel to complete the recharge process. Using this system, a motorist would drive into a fuel station, receive fresh fuel and drive away. Peter Bruce, an expert in new materials for energy storage devices at St Andrews University, UK, comments: 'Finding ways to store more energy than is possible at present is a key challenge and imaginative solutions are necessary. Replacing the zinc in a zinc-air primary battery with a vanadium boride anode is certainly interesting. However, it does raise a number of challenges for practical devices, such as recharging the batteries, and more scientific questions to be answered.' Licht acknowledges that there is lots of work to do before the fuel cell can be commercialised. 'This is a first study demonstrating the very high capacity of the cell. Engineering details, systems optimisation and scale-up need to be developed,' he says. Link to journal articleRenewable highest capacity VB2/air energy storage Stuart Licht, Huiming Wu, Xingwen Yu and Yufei Wang, Chem. Commun., 2008, 3257 DOI: 10.1039/b807929c |
36楼2008-11-13 00:21:18
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Roiser future for solar energy conversion (Nanowerk News) Recent progress in dye-sensitized solar cells (DSCs) research and development, which use innovative light-harvesting dye (the "sensitizer"  to improve the optical absorption coefficient of the stained nanostructured electrodes, might color our dimming future energy security with a tint of rose, despite the looming depletion of fossil fuels. Costing only 10-20% of their silicon counterparts, the new devices might make it affordable for much more people to utilize solar energy, a handy renewable energy source. A research group at the Chinese Academy of Sciences (CAS) Changchun Institute of Applied Chemistry (CIAC) headed by Prof. WANG Peng, in cooperation with a lab at the Swiss Federal Institute of Technology (EPFL) led by Prof. Michael Grätzel, reports in the Journal of American Chemical Society (JACS) two new dyes on July 22, which hit strikingly high energy conversion efficiencies and meanwhile demonstrate good stability under harsh thermal and light-soaking dual stress. This work successfully solves the dilemma between efficiency and stability that has bothered the scientists for a long time and therefore will remove a big hurdle to the commercialized application of DSCs, as anticipated by the researchers. A flexible dye-sensitized solar cell with a solvent-free ionic liquid electrolyte. (Image: G24i Ltd.) A preliminary test shows that one of the new dyes, coded C101, demonstrates a conversion efficiency up to 11.0~11.3%, when working along with an acetonitrile-based electrolyte and measured under the air mass 1.5 global (AM 1.5G) illumination. This performance keeps abreast with the record-holder sensitizers, the N719 and N749 invented by Grätzel's lab. Moreover, the C101 proves to remain stable and retain over 95% of its initial efficiency after soaking in intensive full sunlight for 1,000 hours at 60°C. In contrast, the N719 and N749 both fail to stand long-term thermal and light-soaking stress. So far, among the only three dyes in the world that hit the benchmark of 11% efficiency, the C101 is the most robust in terms of thermal and photochemical stability. Actually, this productive team already initially solved the efficiency-stability dilemma about four months ago. On 4 April, the team reported in the Chemical Communications a novel heteroleptic ruthenium sensitizer that showed an overall conversion efficiency of 10.53% and kept stable under prolonged thermal and light-soaking stress if low-volatility electrolytes were used. More encouragingly, this dye could demonstrate an overall power conversion efficiencies over 10.7% if exposed to various lower light intensities. Wang's team has also solved another dilemma by introducing a novel concept of eutectic melts in electrolyte development. High-performance DSCs often use volatile solvents as electrolytes. This makes it very impractical for outdoor application, because the solvents tend to evaporate very soon in the sunlight due to the heating, and might leak or permeate through cell encapsulations. This would counteract its low cost and relatively high efficiency because its potential commercial production would involve costly sealing. Later efforts to reach better thermal stability by replacing the solvents with ionic liquids, namely salts that melt at a room temperature, however, was frustrated by the low efficiency and poor optical stability of the new devices. In this context, Wang and his colleagues creatively introduced the concept of using eutectic melts to produce solvent-free liquid redox electrolytes. Eutectic is a magical phenomenon in which compounds with different and relatively high melting points, melt together at a much lower temperature when mixed at certain molar ratios. In their work published in Nature Material on June 29, the group mixed three solid imidazolium iodides, which are non-conductive solids at room temperature, in certain molar ratios. As a result they got a ternary melt with a melting point below 0ºC and strikingly high conductivity at ambient temperature. The ensuing experiments showed that DSCs based on a ternary melt reached excellent stability and an efficiency of 8.2% under AM 1.5G, which set a benchmark for solvent-free DSCs. The team is still optimizing the cell parameters to explore the full potential of the new sensitizers. When asked about the potential maximum efficiency of his new inventions, like the heteroleptic ruthenium sensitizer reported in his ChemComm paper, Wang frankly remarks that what interests him the most is not the efficiency, though he gives a rough estimate, 13% under AM 1.5G. Compared with efficiency records achieved in experiments with toxic and volatile electrolytes containing acetonitrile, he emphasizes more on stability and production costs, which have more important practical implications. Indeed, his invention of solvent-free ionic liquid electrolytes based on eutectic melts and high-performance metal-free sensitizers both target the practical needs in industrialized production. Earlier on 27 June, his team synthesized and reported in the JACS an organic sensitizer coded C203 with excellent stability. This marked a milestone because instability had been a major defect for most previously reported organic dyes. More encouragingly, an experimental DSC with 7% conversion rate was successfully formed by combining the C203 with the newly developed eutectic-based electrolyte, and tests showed that the output photocurrent was comparable to that of the DSCs based on volatile electrolytes. The DSC is seen as a promising alternative to silicon solar cells because of its pretty high performance/cost ratio and better sensitivity to weak lights compared to the latter. And the discoveries published in the past few months bring it even closer to real application. "The conceptual DSC patent is out of protection since last April," comments Wang, "I am very confident that the DSC will enter the market very soon and may take over the market share currently held by silicon cells in time." In the meantime, sources say that the G24 Innovations in UK, a large-scale manufacturer of solar cells, has been applying DSC technologies, and more excitingly, it has just got a big order for these flexible devices. This company is reported to be also interested in Wang's new inventions. Despite the fact that currently DSCs present efficiencies only less than a half of what the best silicon cells, which is 24.7%, Wang is optimistic about the future market of DSCs. "It should be realized that, with this relatively low efficiencies, DSCs have already provided a fairly high practical output of electricity power, about 70~80% of silicon cells, according to an outdoor testing report by Aisin Seiki and Toyota Motor," Wang emphasizes. "This is because of their better sensitivity to weak lights," he explains: "and they can deal with diffusive sunlight very efficiently, due to their nanostructure. The best DSC under the diffusive sunlight has reached an overall efficiency of 14% in outdoor tests." In addition, under low light intensities, for example, under room light, a DSC exhibits much higher conversion efficiency than silicon cells, according to Wang. Based on the above reasons, it is estimated that stable, low-cost, flexible and lightweight DSCs are attractive even if their solar conversion efficiencies are moderate, like between 5-9%. So far, Wang and his co-workers have employed their new dyes in conjugation with their best electrolytes and state-of-the-art titania films to fabricate DSCs with enhanced comprehensive properties and performance. Their new ideas yield fantastic devices of long-term stability that hit a record efficiency of 10%. Another result is the first solvent-free DSC in the world that reaches a conversion rate of 9.1%. These inventions have got authorized patents and will be published very soon. "I believe," added Wang, "Overall, the DSC is the most promising technique which can compete with the sate-of-the-art photovoltaic cells in the future." Source: Chinese Academy of Sciences |
37楼2008-11-13 00:21:38
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Cooler fuel cells 31 July 2008 Solid oxide fuel cells, which generate electricity at around 700°C, may be able to operate at room temperature - thanks to a new layered material that is remarkably efficient at conducting oxygen ions. A solid oxide fuel cell (SOFC) directly generates electricity by reacting oxygen anions (produced at the cathode from oxygen gas) with a hydrogen rich fuel (at the anode). The efficiency of an SOFC depends strongly on how quickly oxygen ions can migrate from one electrode to another, through a solid ceramic electrolyte. Yttria-stabilized zirconia (YSZ) is the electrolyte of choice, being mechanically stable and unreactive with an SOFC's electrodes. But to get the fuel cell working efficiently, very high temperatures (above 700°C) are required - bumping up the costs and startup time of electricity production. As Jacobo Santamaría, at the Complutense University of Madrid, explains, cutting down the thickness of the electrolyte to a few nanometres, using modern thin-film growth techniques - and introducing new materials into the electrolyte, such as gadolinium-doped cerium and lanthanum gallates - has helped to improve conductivity, but only to the level of 500°C working temperatures. He and colleagues in the US and Spain have now made an electrolyte so conductive to oxygen ions that it operates best at a mere 84°C, and has excellent projected conductivity even at room temperature. 'With our new material, the oxygen ionic conductivity is enhanced up to one hundred million times', Santamaría says. 3D model of the YSZ/STO interface, showing oxygen vacancies (shaded red spheres) that give rise to the enhanced conductivity of the new electrolyte The researchers grew a 1-nanometre thick layer of conducting YSZ sandwiched between 10-nanometre-thick layers of insulating strontium titanate (STO). STO's crystalline structure mismatches with YSZ's, leading to disordered ions at interfaces between the two. That, says Santamaría, accounts for the dramatic rise in oxygen ion flow, as many more gaps (oxygen vacancies) appear at the interface. 'This interface effect could be used in single-chamber solid oxide fuel cells, allowing their application at room temperature', comments Igor Efimov, an electrochemist at Leicester University, UK. The researchers are now planning further experiments that will allow them to understand in more detail what is happening at the interface. The next step, says Santamaría, is to substitute STO for another material with a crystalline structure more similar to YSZ's, to investigate the team's interface hypothesis. Kira Welter Enjoy this story? Spread the word using the 'tools' menu on the left ReferencesJ Garcia-Barriocanal et al, Science, 2008, 321, 676 Chemistry World |
38楼2008-11-13 00:22:17
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Silicon nanowires boost solar cells Solar cells made from silicon nanowires could give "classic" silicon-based photovoltaics or other types of solid-state solar cells a run for their money, say researchers at Hong Kong City University. Shuit-Tong Lee and colleagues have succeeded in producing silicon nanowire array photoelectrochemical solar cells that show more efficient light absorption per unit device and thus higher light conversion efficiency at a lower cost than conventional silicon-based cells. The way that the new arrays were prepared also means they could easily be scaled up for large-area applications. SiNW arrays Although silicon-based solar cells are one of the most important products currently on the market, they remain expensive. Silicon nanowire-based photoelectrochemical solar cells could offer a solution to this problem, says Lee. Superior properties The cells prepared by Lee's team show excellent optical anti-reflectivity over the entire solar spectrum (300–1000 nm), a wide spectral bandwidth and outstanding surface defect-induced electrical conductivity (which originates from the silicon wafers used), compared with other low-cost semiconductor materials, such as nanocrystalline titanium dioxide. Moreover, thanks to the large surface-volume ratio, silicon nanowires (SiNWs) provide a larger area per unit of material. This means a larger area for light absorption, larger interface areas for exciton dissociation for separating charge carriers (electrons and holes) and an excellent conducting path for transporting the charge carriers away. Low cost "All of these superior properties translate into the highest light conversion and therefore low cost," Lee told nanotechweb.org. The researchers prepared their SiNWs by simple metal-catalyzed etching of silicon wafers that are commonly used in the semiconductor industry and which are readily available at reasonable cost. Wafer-scale SiNWs can be etched from any Si(100) wafers in a hydrofluoric-silver nitrate solution or a hydrofluoric solution containing an oxidizing agent, such as hydrogen peroxide, using silver or other suitable metals as the etching catalyst. The electroless etching technique allows for rapid wafer-scale fabrication of SiNWs that have good electrical conductivity without the need for doping. "While there are other ways of making SiNWs, our proprietary method via metal-catalyzed silicon etching has many advantages," explained Lee. "It produces SiNW in air over large areas as oriented arrays and at low cost from silicon wafers of any desired conductivity." In contrast, SiNWs prepared by chemical vapour deposition are more expensive to make, are produced in smaller quantities and require doping to achieve conductivity. The team now plans to investigate the effect of surface modification (such as surface passivation) on the performance of SiNW photoelectrochemical solar cells. "We also hope to design better cell structure and aim to further optimize and enhance the conversion efficiency for commercializing these cells," revealed Lee. "We are especially interested in working with industry to convert our technology into a solar-cell product as soon as possible." The work was reported in Applied Physics Letters. Source: nanotechweb.org |
39楼2008-11-13 00:24:01
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Fraunhofer Institute achieves 39.7% record efficiency for solar cells (Nanowerk News) At 39.7% efficiency for a multi-junction solar cell, researchers at the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg have exceeded their own European record of 37.6% which they achieved just a short time ago. III-V semiconductor multi-junction solar cells are used in photovoltaic concentrator technology for solar power stations. “We have improved the contact structures of our solar cells,” says Frank Dimroth, Head of the III-V – Epitaxy and Solar Cells Group at Fraunhofer ISE. “As a result, using the same semiconductor structures, we now achieve the higher efficiency when converting sunlight into electricity.” For the utilization in photovoltaic concentrator systems, the optimal efficiency of multi-junction solar cells must often be achieved between 300 - 600 suns, that is, at a sunlight concentration factor of 300 – 600. The metallization of the front side makes the main difference for different concentration factors. In the front grid the current is conducted through a network of thin wires (see figure 1) from the middle of the solar cell to the edge, where it is then picked up by a 50 µm gold wire. Particularly under concentrated sunlight, the structure of this metal network is decisive. For one, the metal wires must be big enough to transport, with low resistance, the large currents which are generated under concentrated sunlight. On the other hand, the wires must be as small as possible since the sunlight cannot penetrate through metal and thus the cell area covered by metal cannot be used for the electrical conversion. For the past two years at Fraunhofer ISE, work is being performed on a new program for the theoretical calculation of optimal contact structures. Based on this work sponsored by the EU Project Fullspectrum (SES6-CT-2003-502620), solar cells holding the newest record efficiencies were developed. These cells are especially suitable for situations of inhomogeneous radiation, as occurs in the case of concentrated sunlight. These solar cells are installed in the concentrator modules of the type FLATCON® at Fraunhofer ISE and at the spin-off company Concentrix Solar GmbH, among others. “We are very pleased to have advanced a further decisive step in such a short amount of time,” says Dr. Andreas Bett, Department Head at Fraunhofer ISE. “Highest conversion efficiencies help the young technology to become market competitive and to further sink the costs of generating electricity from the sun for the future.” For more than ten years, researchers at Fraunhofer ISE have been developing multi-junction solar cells with highest efficiencies. One emphasis here is on the so-called metamorphic (lattice mismatched) triple-junction solar cells made out of Ga0.35In0.65P, Ga0.83In0.17As and Ge, which have an especially high theoretical efficiency potential. The solar cell structures consist of more than 30 single layers, which are deposited on a germanium substrate by means of metal-organic vapour-phase epitaxy (MOVPE). Today such multi-junction III-V semiconductor solar cells achieve the highest conversion efficiency worldwide by far. Due to the large material and manufacturing costs, however, they are only used in concentrating PV systems and in space. Source: Fraunhofer Institute for Solar Energy Systems |
40楼2008-11-13 00:24:20
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Copper future for solar cells 24 September 2008 Lewis Brindley /Turin, Italy Rare ruthenium complexes that are a key component of dye-sensitised solar cells could in future be replaced by molecules based on copper, say Swiss researchers. Dye-sensitised solar cells (which use absorbent dyes to convert sunlight into photoelectrons and a separate semiconductor to generate a current) are promising candidates to replace conventional silicon solar panels, since they are cheaper and more flexible - though not yet as efficient. Though only small amounts of a ruthenium-based dye are required in the solar cell, ruthenium is one of the rarest metals on Earth, so the team at the University of Basel are hoping to switch to complexes of a more common metal. Presenting their work at the 2nd EuCheMS chemistry congress in Turin, Italy, Ana Hernandez Redondo explained that the team have showed that complexes of copper(I) can interact with light in a similar way to ruthenium. The key, they revealed, is to keep copper in the +1 oxidation state, which is achieved by 6,6'-disubstituted 2,2'-bipyridine ligands that grip the copper ion tightly, preventing it from oxidising into copper(II). Substituted bipyridines form strong complexes with Cu(I) 'Our first-generation copper-based cells showed light conversion efficiencies of 2.3 per cent, which is around four times lower than ruthenium complexes currently on the market,' said Redondo. 'But our research indicates that copper polypyridine complexes are a candidate to be the sensitisers [dyes] of the future,' she added, pointing out that the efficiency of the new complexes is comparable to early ruthenium compounds first made during the 1980s. In a recently-published paper, the researchers estimate that the cost of the copper complex is 'an order of magnitude lower' than that of the ruthenium sensitiser. Redondo says the team are confident that small modifications to the ligand structure, based on past experience with ruthenium complexes, should boost light conversion efficiencies considerably. They have already made progress, she announced at the conference, by integrating an additional phenyl group in the polypyridine ligand. This gave greater light absorption over the visible spectrum and the team expected to see a jump in conversion efficiency. Dye-sensitised solar cell inventor Michael Grätzel, also speaking at the Turin conference, praised the work, saying that 'there is a great need to tailor the best sensitisers in order to continue optimising the efficiency and cost of these cells.' Enjoy this story? Spread the word using the 'tools' menu on the left. ReferencesT Bessho et al, Chem.Commun., 2008, 3717 (DOI: 10.1039/b808491b) |
41楼2008-11-13 00:25:04
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Sugar-powered electronics 03 October 2008 Japanese scientists have made a biofuel cell that produces enough power to run an mp3 player or a remote controlled car. Inspired by power generation in living organisms, Tsuyonobu Hatazawa, from the Sony Corporation, Kanagawa, and colleagues developed a bio-battery that generates electricity from glucose using enzymes as catalysts. Four biofuel cell units in series can power an mp3 player with speakers A typical biofuel cell consists of an anode and a cathode separated by a proton-conducting membrane. A renewable fuel, such as a sugar, is oxidised by microorganisms at the anode, generating electrons and protons. The protons migrate through the membrane to the cathode while the electrons are transferred to the cathode by an external circuit. The electrons and protons combine with oxygen at the cathode to form water. Until now, the energy output from biofuel cells has been too low for practical applications. Electron transfer in a biofuel cell can be slow so Hatazawa used a naphthoquinone derivative - known as an electron transfer mediator - to shuttle electrons between the electrodes and enzymes. This increased the current density - a measure of the rate of an electrochemical reaction - and increased the power output. "The research will give much needed impetus to the development of useful biofuel cells" - Adam Heller, The University of Texas at Austin, US To increase the current density further, Hatazawa packed the mediator and enzymes on to a carbon-fibre anode. The large surface area and porosity of the electrode avoided disruption to glucose transport and maintained enzyme activity. They used a similar design to optimise the cathode so it supplied oxygen efficiently to the fuel cell. When the researchers stacked four of the cells together, they achieved a power output of 100 milliwatts - enough to run an mp3 player with speakers or a small remote controlled car. Adam Heller, an expert in bioelectrochemistry from The University of Texas at Austin, US, says the research 'will give much needed impetus to the development of useful biofuel cells, after years of studies aimed at unachievable goals'. Nicola Burton Link to journal article A high-power glucose/oxygen biofuel cell operating under quiescent conditions Hideki Sakai, Takaaki Nakagawa, Yuichi Tokita, Tsuyonobu Hatazawa, Tokuji Ikeda, Seiya Tsujimura and Kenji Kano, Energy Environ. Sci., 2008 DOI: 10.1039/b809841g Also of interest Simply biofuels A simple enzyme-based biofuel cell has been made by a team of Japanese scientists. Ironing out fuel cells A simple iron complex could pave the way for new oxygen reduction catalysts with potential uses in low-temperature fuel cells Instant insight: Fuel cells get cooler Solid oxide fuel cells can be used at lower temperatures thanks to advances in materials and engineering Chemistry World. |
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43楼2008-11-13 00:26:10
Chip Makers Invest In Solar Power
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IBM and Intel have competing solar cell initiativesTwo giants of silicon-based computer chips are setting their sights on solar power with major initiatives. IBM is teaming up with Japanese photolithography materials producer Tokyo Ohka Kogyo (TOK) to develop copper-indium-gallium-selenide (CIGS) solar cell technology. And Intel is spinning off SpectraWatt, which will make conventional crystalline silicon-based cells. IBM and TOK say CIGS cells will be cheaper than silicon cells because they can be printed on thin glass or even flexible substrates. Conventional cells are based on slices of silicon housed in elaborate enclosures. "Our goal is to develop more efficient photovoltaic structures that would reduce the cost, minimize the complexity, and improve the flexibility of producing solar electric power," says Tze-Chiang Chen, IBM vice president of science and technology. Meanwhile, Intel, along with Goldman Sachs subsidiary Cogentrix Energy and other investors, are putting $50 million into SpectraWatt. The new firm will focus on improving manufacturing processes to make traditional solar cells cheaper. The company plans to start up its first factory, which will be in Oregon, by the middle of next year. Market research firm Photon Consulting expects that the world market for solar technology, $30 billion in 2007, will grow at an annual rate of about 40% in the coming years. June 20, 2008 Chemical & Engineering News |
44楼2008-11-13 00:26:47
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Robert F. Service Today's solar cells do a fair job of converting visible light into electricity, but they ignore lower energy infrared (IR) photons, or heat, which don't have enough energy to generate electricity in semiconductors. At the meeting, researchers from the Idaho National Laboratory (INL) in Idaho Falls reported harvesting IR photons with arrays of antennas akin to those on televisions and in cell phones, a first step toward solar cells that convert heat to electricity. If the approach pans out, it could lead to solar cells capable of generating electricity after sunset and using the waste heat from industrial plants. "It's certainly an intriguing idea," says Michael Naughton, a physicist at Boston College in Chestnut Hill, Massachusetts, whose group has built related antennas. But he notes that converting the energy from the collected IR light to electricity will require a separate set of advances. Says Naughton: "Either it has no chance of working, or it will be fantastic." The notion of using antennas to capture electromagnetic waves and then convert that energy to electricity is decades old. In 1964, William Brown, an engineer at the U.S. aerospace company Raytheon, demonstrated a flying helicopter that absorbed microwaves and converted their energy to DC power to run a small engine. At the heart of the helicopter's success was a two-part device called a "rectenna": a microwave-absorbing antenna combined with a "rectifier" that converts the microwave energy to electricity. More recent are proposals to transmit microwave energy to Earth from arrays of solar collectors in space. Several years ago, researchers led by Steven Novack at INL set out to capture and convert IR light, which has a wavelength two to five orders of magnitude shorter than microwaves. That meant the size of each antenna needed to be in the micrometer scale with numerous features in the nanometer range. To capture enough IR photons, Novack and his colleagues needed arrays with millions of the antennas side by side. The good news was that instead of having to use exotic semiconductor alloys to capture the light, they could do so by patterning gold in square spiral structures. Novack's team worked out a way to stamp out millions of gold spiral arrays on either silicon or cheap, flexible plastics. At the meeting, Novack reported that the arrays on silicon capture some 80% of the IR photons that hit them, whereas those on plastic manage a respectable 40% to 50%. Gotcha. Arrays of gold spiral-shaped antennas absorb infrared photons, or heat, triggering electrons in the antennas to oscillate at 30 trillion times per second. Researchers hope those excited electrons will lead to a new form of solar power. CREDIT: IDAHO NATIONAL LABORATORY Novack and his colleagues still need to figure out how to get the power out of the antennas. When the IR photons hit the array, they cause electrons in the gold to oscillate back and forth at a frequency of 30 terahertz, or 30 trillion times a second. Conventional electronics operate with a current that oscillates at a plodding 60 times a second. That means Novack's team needs to find devices that can either step down the terahertz electrons or convert them into a DC current. Unfortunately, Novack and Naughton know of no devices--commercial or otherwise--that can do that, though diodes and rectifiers do the job at lower frequencies. But Novack says theoretical work suggests that sandwichlike devices made from three metal layers separated by ultrathin insulating layers might step down the frequency. And both Novack and Naughton say that a recent surge in terahertz-frequency research is producing rapid advances. Novack says devices that convert to electricity even 30% to 40% of the IR energy absorbed by the antennas could lead to solar cells that beat the efficiency of crystalline silicon cells with a cheap and simple technology that can be printed like newspapers. http://www.sciencemag.org/cgi/content/full/320/5883/1585 |
45楼2008-11-13 00:27:47
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Instant insight: Fuel cells get cooler Brett, Atkinson, Brandon and Skinner of the Imperial College Fuel Cell Network, London, UK, look at how advances in materials and engineering are presenting new opportunities for solid oxide fuel cells. Intermediate temperature solid oxide fuel cells hold the middle ground in the temperature scale of fuel cell operation Fuel cells are electrochemical energy conversion devices that convert the chemical energy in fuel directly into electricity and heat without combustion. Simplistically, a fuel cell can be viewed as a cross between a battery, which converts chemical energy directly into electrical energy, and a heat engine, a continuously fuelled, air breathing device. There is a range of different fuel cell technologies, each with its own materials set and operation temperature, ranging from room temperature to over 1000 degrees Celsius. However, they all share the characteristics of high efficiency, no moving parts, quiet operation and low or zero emissions. "Operating at intermediate temperature opens up a new range of applications and opportunities for solid oxide fuel cells" There is no consensus as to the optimal operating temperature of fuel cells; the preferred temperature of operation depends to a large extent on the application. However, there is significant effort to raise the operating temperature of polymer electrolyte fuel cells (PEFCs) and reduce the operating temperature of solid oxide fuel cells (SOFCs). PEFCs currently operate at around 80 degrees Celsius and are used in automotives, mobile phones and laptops. SOFCs operate at more than 800 degrees Celsius and use a ceramic oxide ion-conducting electrolyte to generate energy on a large scale. Advances in the chemistry and processing of materials are allowing the operating temperature of SOFCs to be lowered into the so-called 'intermediate temperature' (IT) region of 500 to 750 degrees Celsius. The IT-SOFC opens up a new range of applications and opportunities for SOFCs in areas formally dominated by PEFCs, while maintaining the ability to operate on hydrocarbon fuels and produce high quality heat. Operation in the IT range expands the choice of materials and stack designs that can be used compared to conventional high temperature (HT) SOFCs. Lower temperature operation affords more rapid start-up, improved durability, reduced system cost and more robust construction through the use of compressive seals and metallic construction materials (as opposed to the all-ceramic HT-SOFCs). There are two main routes by which SOFCs can be used at lower temperatures while still attaining comparable performance to the higher temperature technology. The first involves reducing the thickness of the electrolyte to the order of a few 10s of micrometres, so ions can travel more easily through the fuel cell. Alternatively, the same result can be achieved by improving the electrolyte's ionic conductivity at lower temperatures and the electrodes' electrochemical performance. "Intermediate temperature solid oxide fuel cells are a strong contender to be the first fuel cell technology to reach mass market" The range of new applications for the IT-SOFC includes soldiers' personal power supplies, traction power for vehicles, remote telecommunications, power for isolated communities and back-up power units for trucks. However, it is the small-scale combined heat and power market where the IT-SOFC is particularly well suited. Operating on natural gas and with a heat-to-power ratio close to one, IT-SOFCs with an electrical power rating of about one kilowatt are expected to be popular as combined heat and power sources for use in the home. Indeed, IT-SOFCs have the potential to be the simplest fuel cell system and are a strong contender to be the first fuel cell technology to reach mass market. As with all fuel cells, the cost of IT-SOFCs must be reduced for them to compete in the market with current technologies. Using less, and cheaper, material is necessary; moving to lower temperature operation represents a significant step in this direction. Scientists still need to develop IT-SOFCs with commercially meaningful levels of durability. Fundamental studies are improving our understanding of processes such as electrode sintering, anode-fuel interaction, electrocatalyst poisoning and the mechanical properties of electrolytes and support structures. Link to journal articleIntermediate temperature solid oxide fuel cells Daniel J. L. Brett, Alan Atkinson, Nigel P. Brandon and Stephen J. Skinner, Chem. Soc. Rev., 2008 DOI: 10.1039/b612060c 27 June 2008 Chemical Technology |
46楼2008-11-13 00:29:06
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Oxygen Ions For Fuel Cells Get Loose At Low(er) Temperatures Seeking to understand a new fuel cell material, a research team working at the National Institute of Standards and Technology (NIST), in collaboration with the University of Liverpool, has uncovered a novel structure that moves oxygen ions through the cell at substantially lower temperatures than previously thought possible. The finding may be key to solving fuel cell reliability issues and lead to reduced operating costs in high-performance stationary fuel cells. Electricity is produced in fuel cells from the electrochemical reaction between a hydrogen-rich fuel and oxygen that produces electric current and water. Research on small fuel cells for cars has dominated the news, but stationary fuel cells are the Goliaths--operating at up to 70 percent efficiency and providing enough electricity--up to 100 megawatts--to power small cities, hospitals, military installations or airports without relying on the electric power grid. Smaller versions are being considered for auxiliary power units in such applications as refrigeration trucks to reduce engine idling. They are called "solid oxide" fuel cells (SOFCs) because the heart of the cell is a solid electrolyte that transports oxygen ions extracted from air to meet with hydrogen atoms. This alchemy traditionally requires high temperatures--about 850 degrees Celsius in conventional SOFCs--and therefore long startup times, ranging from 45 minutes to eight hours. The high temperatures necessitate more expensive materials and higher operating costs, so stationary fuel cell research is focused on lowering operating temperatures as well as shortening startup times. The U.S. Department of Energy's goal is to slash the startup time to two minutes. Chemists at the University of Liverpool fabricated a new oxygen ion electrolyte material of lanthanum, strontium, gallium and oxygen and sent it to the NIST Center for Neutron Research (NCNR) to investigate with collaborators from NIST, the University of Maryland and University College London. Neutrons provide an atomic-scale view of materials so scientists can "see" what is happening at that level. The oxygen ions in the new materials become mobile at 600 degrees C, much lower than previously studied materials. Researchers suspected the reason lay in the location of the oxygen ions in the crystal framework of the compound. The neutron probes allowed them to determine the basic crystal structure that held the lanthanum, strontium, gallium and oxygen atoms, however the exact nature of the extra oxygen ions was unclear. NCNR researchers recommended borrowing a method from radio astronomy called maximum entropy analysis. "When astronomers are not able to visualize a specific part of an image because it constitutes such a small part of the total information collected, they utilize a part of applied mathematics called information theory to reconstruct a sharper image," explains NCNR researcher Mark Green. "The combination of neutron diffraction and maximum entropy analysis not only allowed us to determine the location of additional oxygen ions outside of the basic framework, but revealed a new mechanism for ion conduction." "It allows us to take a fundamentally different approach in the design of future materials, so that we can harness this new mechanism for oxide ion conduction and produce lower operating fuel cells," says Green. "This type of work is very important to us, which is why as part of the NCNR expansion we are developing a new materials diffractometer that will greatly enhance our capabilities in energy related research." Researchers determined that a new material for fuel cells releases oxygen ions easily at low temperatures because many of the oxygen ions -— marked here as O4 —- are not closely bound to the material's crystal framework. (Credit: X. Kuang, University of Liverpool) Journal reference: * Kuang et al. Interstitial oxide ion conductivity in the layered tetrahedral network melilite structure. Nature Materials, 2008; 7 (6): 498 DOI: 10.1038/nmat2201 NIST June 27, 2008 |
47楼2008-11-13 00:29:40
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New efficiency benchmark for dye-sensitized solar cells (Nanowerk News) In a paper published online June 29 in the journal Nature Materials, EPFL professor Michael Grätzel, Shaik Zakeeruddin and colleagues from the Changchun Institute of Applied Chemistry at the Chinese Academy of Sciences have achieved a record light conversion efficiency of 8.2% in solvent-free dye-sensitized solar cells. This breakthrough in efficiency without the use of volatile organic solvents will make it possible to pursue large scale, outdoor practical application of lightweight, inexpensive, flexible dye-sensitized solar films that are stable over long periods of light and heat exposure. Dye-sensitized solar cell technology, invented by Michael Grätzel at EPFL in the 1990s, shows great promise as a cheap alternative to expensive silicon solar cells. Dye-sensitized cells imitate the way that plants and certain algae convert sunlight into energy. The cells are made up of a porous film of tiny (nanometer sized) white pigment particles made out of titanium dioxide. The latter are covered with a layer of dye which is in contact with an electrolyte solution. When solar radiation hits the dye it injects a negative charge in the pigment nanoparticle and a positive charge into the electrolyte resulting in the conversion of sunlight into electrical energy. The cells are inexpensive, easy to produce and can withstand long exposure to light and heat compared with traditional silicon-based solar cells. Currently, state-of-the-art dye-sensitized cells have an overall light conversion efficiency greater than 11%, still about two times lower than silicon cell technology. A major drawback to the dye-sensitized cell technology is the electrolyte solution, which is made up of volatile organic solvents and must be carefully sealed. This, along with the fact that the solvents permeate plastics, has precluded large-scale outdoor application and integration into flexible structures. To overcome these limitations, Grätzel and his colleagues developed a new concept -- a mixture of three solid salts as an alternative to using organic solvents as an electrolyte solution. When the three solid components are mixed together in the right proportion they turn into a melt showing excellent stability and efficiency. Grätzel is confident that further development of these types of electrolyte mixtures will lead to large-scale practical application of dye-sensitized solar cell technology, reinforcing solar energy's role as a cornerstone of alternative energy production. Source: Ecole Polytechnique Fédérale de Lausanne |
48楼2008-11-13 00:29:53
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Bendy solar cells that can take the heat Chemists in Switzerland and China have used a liquid electrolyte to make flexible solar cells that are better than current devices at withstanding heat from the sun's rays. The new type of dye-sensitised solar cell (DSC) is the latest product from Michael Grätzel, who was the first to make DSCs in 1991. 'This cell will make an important contribution to the market for power generation in the future,' says Grätzel, director of the laboratory of photonics and interfaces at the Swiss Federal Institute of Technology in Lausanne (EPFL). In contrast to traditional solid silicon semiconductor-based cells, the DSC uses light-sensitive dye molecules in a liquid electrolyte. The liquid electrolyte is in contact with all parts of the cell at once, making it a highly efficient conductor. This also makes the cell flexible - so cells could be used in portable electronic devices. But using DSCs in large outdoor arrays has been difficult because the liquid electrolyte - often a volatile solvent - can evaporate at the high temperatures cells reach in direct sunlight. Recent designs have made use of ionic liquids: salts with a low melting point that are liquid at room temperature. Although these solvent-free DSCs are more stable to heat, they can be inefficient. Grätzel's team has solved this problem by using a 'eutectic melt' - a mixture of several solids that form a liquid when combined. One example of a eutectic melt is seen when salt is used to de-ice roads. Solid sodium chloride and solid water (ice) mix to form liquid saltwater. 'We mixed three solid imidazolium iodides to form a highly conductive, ambient-temperature liquid,' says Peng Wang, who worked on the project at the Chinese Academy of Sciences in Changchun, China. 'In contrast, the individual ingredients are solid and non-conductive at room-temperature.' The advantage of using these eutectic mixtures, Wang explains, is that they have much higher conductivities than ordinary ionic liquids but remain extremely stable at high temperatures. The solar cells can turn about 8 per cent of the sunlight that falls on them into electricity but Grätzel believes that their efficiency could be improved further. 'The maximum power conversion efficiency that can be reached by this kind of solar cell is around 31 per cent,' he says. Commenting on the work, Juan Bisquert, who works on dye-sensitised solar cells at Jaume I University in Castellón de la Plana, Spain, says, 'The 8 per cent efficiency is comparatively high, as this is approaching the amorphous silicon technologies that are on the market.' ReferencesY Bai et al, Nature Materials, 2008, DOI: 10.1038/nmat2224 July 1, 2008 Chemistry World |
49楼2008-11-13 00:30:06
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Ionic-Liquid Solar Cells Blending solids leads to stable ionic liquid and efficient energy conversion deviceChemists in China and Switzerland have designed a robust and efficient dye-sensitized solar cell (DSC) based on a solvent-free mixture of three imidazolium compounds (Nat. Mater., DOI: 10.1038/nmat2224). Each of the substances is a solid under ambient conditions. But when mixed in equimolar ratios, they form a eutectic melt, thereby providing a three-component, room-temperature ionic liquid. MITCH JACOBY/C&EN Grätzel The potential for low cost and flexibility makes DSCs attractive alternatives to conventional solar energy conversion devices based on crystalline silicon. A key limitation of most DSC designs is the need for electrolytes dissolved in organic solvents, which can evaporate and permeate cell components. Researchers have had success sidestepping the evaporation and leakage problems by using solvent-free ionic liquids, but most of these compounds decompose under prolonged exposure to sunlight. Now, a team led by Peng Wang of the Institute of Applied Chemistry, in Changchun, China, and Michael Grätzel of the Swiss Federal Institute of Technology, in Lausanne, formed a novel ionic liquid by blending 1-ethyl-3-methylimidazolium iodide with the dimethyl and allyl-methyl analogs. Compared with other ionic liquid DSCs, solar cells based on the new substance are more resistant to decomposition and exhibit 1–2% higher solar conversion efficiencies. July 2, 2008 C & E N |
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