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carlosangel

新虫 (初入文坛)

[交流] 翻译一篇化学论文~~

(一些单位乱码了，不影响翻译)
High-Yield Synthesis of NiO Nanoplatelets and Their Excellent Electrochemical Performance



ABSTRACT: We demonstrate a new approach to successfully synthesize on a large scale single-crystalline nickel oxide nanoplatelets with an interesting porous structure. The as-obtained oxide nanoplatelets were characterized by a variety of techniques, such as X-ray powder diffraction, transmission electron microscopy, thermogravimetric analysis, BET surface area measurement, and electrochemical test. The electrochemical result exhibits that the electrochemical performance of the obtained nickel oxide nanoplatelets with the novel morphology has been further improved in contrast to that of the ultrafine oxide nanoparticles with average particle size of 9 nm. It suggests that the unique platelet-like nanostructure is helpful in improving the electrochemical performance of the
oxide.
                                            Introduction
      Transitional metal oxides and hydroxides, such as cobalt, iron,and nickel, have attracted increasing attention owing to their potential in a variety of field. Among them, nickel oxide, as one of the relatively few metal oxides with p-type semiconductivity, has been extensively investigated because of the stable band gap. NiO is very a prosperous material, being widely used in practice as a catalyst, as electrode material for lithium ion batteries and fuel cells, in electrochromic films, in electrochemical supercapacitors, and in dye-sensitized photocathodes.
       With advancements in all areas of industry and technology,the interest has been focused on nanoscale materials, which stems from the fact that new properties are required at this length scale and, equally important, that these properties change with their size and morphology. Thus, many methods have been
attempted to prepare nanosized nickel oxide, including nanoparticles, nanorings, nanosheets, and nanoribbons.
        In this work, we demonstrate a new approach to fabricate nickel oxide nanocrystals on a large scale attempting to find a new application or improve the existing performance. At first, the single crystalline hydroxide nanoplatelets were synthesized by hydrothermal treatment of nickel acetate and methylamine at relatively low temperature. The shape of the oxide nanoplatelets was sustained by the thermal decomposition of the hydroxide precursor, and the electrochemical performance of the unique nanostructured oxide was investigated. It is expected
to explore a more extensive potential application of transitional metal oxide.
                                          Experimental Section
            All the chemicals were of analytical grade and were used as received without further purification. At first, nickel hydroxide nanoplatelet precursor was prepared by the precipitation and hydrothermal process. In the typical procedure, 10 mmol of freshly precipitated nickel oxalate was dispersed in 20 mL of distilled water, and 20 mL of 0.4 M methylamine solution was added under magnetic stirring at room temperature. The resulting mixture was then transferred into a 60 mL Teflon-lined autoclave, which was sealed and heated at 120 °C for 12h. After the hydrothermal treatment, a green suspension was obtained. The precipitate was separated from the solution by centrifugation, washed repeatedly with distilled water, and dried at 60 °C in a vacuum. Finally, the resulting hydroxide precursor was heated at 400 °C for 2h in air to prepare the oxide product.
      The crystalline phase was identified by powder X-ray diffraction (XRD) using a Philips X’Pert Pro Super diffractometer with graphite monochromatized Cu KR radiation (λ= 1.541 78 A. High-resolution TEM images and selected-area electron diffraction (SAED) patterns were obtained on a JEOL-2010 transmission electron microscope at an acceleration voltage of 200 kV. Thermogravimetric analysis (TG) of the sample was carried out on a Shimadzu TA-50 thermal analyzer at a heating rate of 10 °C min-1 from room temperature to 600 °C in flowing air. N2 adsorption was determined by BET measurements using a NOVA-1000e surface analyzer.
       The electrochemical performance of the oxide was examined witha Teflon cell. The cathode was a mixture of nickel oxide, acetylene black, and polyvinylidene fluoride (PVDF) with weight ratio of 85:10:5. Metallic lithium was used as the negative electrode. The electrolyte was 1 M LiPF6 in a 1:1 mixture of ethylene carbonate (EC)/diethyl carbonate (DEC). The cell was galvanostatically cycled in the range of 3.0-0.5 V. For comparison, the electrochemical performance of
ultrafine NiO nanoparticles with average particle size of 9 nm was also investigated, which was prepared by thermal decomposition of nickel oxalate nanofibers.
                                        Results and Discussion
         Figure 1 displays the X-ray diffraction (XRD) patterns of the as-prepared sample before and after calcinations. All the diffraction peaks of Figure 1a can be indexed as hexagonal β-Ni-(OH)2 with the lattice parameters a =3.128 Å and c = 4.605Å, in good agreement with the reported values (ICDD-JCPDScard No. 14-0117). No obvious peaks for other impurity were detected. Figure 2 shows the TEM images of the hydroxide precursor prepared by the hydrothermal treatment. From the images, one can see that the morphology of the hydroxide is platelet-like with average diameter of 50 nm. Many of the products are irregular hexagonal platelets.
         On the basis of the TG analysis result, the hydroxide precursor was heated at 400 °C for 2 h to ensure the complete decomposition of β-Ni(OH)2. Figure 1b shows the XRD pattern of the as-prepared NiO powder. All the reflections can be indexed to face-centered cubic (fcc) NiO phase with lattice constant a = 4.175 Å (space group Fm3hm [225]), which agrees well with the standard data (JCPDS card No. 47-1049). No peaks due to β-Ni(OH)2 were found from XRD, indicating that β-Ni(OH)2 was completely decomposed to NiO at 400 °C for 2 h, which is also confirmed by the TG measurement. The broadening of the diffraction peaks indicates the small particle size.
          Figure 3 exhibits TEM and HRTEM images of the oxide sample. From Figure 3a,b, the porous NiO nanoplatelets with average diameter of about 60 nm can be clearly observed, and the platelet-like morphology was sustained by the thermal
decomposition of the hydroxide nanoplatelet precursor at 400°C for 2 h in air. The average pore size is about 5 nm. The yield of the platelet-like structures is very high (above 90%). Figure 3c shows the representative nanoplatelets with irregular
hexagonal shape with the angels of adjacent edge of 120°, as indicated by solid lines. A high magnification of an individual nanoplatelet is shown in Figure 3d. The HRTEM image shows a well-defined crystalline structure with a lattice spacing of 1.4
Å, corresponding to the value of the (220) plane of the cubic NiO phase. The inset in Figure 3f shows the corresponding SAED pattern. The ED pattern was taken with an electron beam along the [-111] zone axis, perpendicular to the nanoplatelet
surface. After further investigation on the above results, we confirm that the surface of the nanoplatelets is the {111} plane of the cubic NiO phase, and the adjacent edges with the angles of 120° should correspond to the {110} and {101} planes. ED patterns on different individual nanoplatelets were essentially the same, indicating the single crystalline nature of the NiO nanoplatelets.
          The organic base environment provided by methylamine is vitally important for the formation of the platelet-like hydroxide. If methylamine was replaced by other alkali media, such as ammonia, the platelet-like hydroxide could also be obtained. But the average thickness of the nanoplatelets was doubled, which was not beneficial to the subsequent formation of the porous oxide nanoplatelets. BET (Brunauer-Emmett-Teller) surface areas, calculated from nitrogen adsorption isotherms, show that the surface area of the NiO nanoplatelets is 85 m2/g, which increases significantly compared with that of the nickel hydroxide nanoplatelets (21 m2/g). And the average pore size of the oxide is 4.2 nm, consistent with the TEM observation.
             The electrochemical measurements for the resulting oxide nanoplatelets were carried out at room temperature in a voltage range from 3.0 to 0.5 V at a constant current density of 0.4 mAcm-2. Figure 4 shows the voltage vs discharge capacity curves for nickel oxide nanoparticles (a) and nanoplatelets (b). For the nanoplatelets, the discharge plateau is about at 1.5 V, and the average discharge capacity can reach ca. 700 mA h g-1 for the first 20 cycles, corresponding to the intercalation of 1.95 Li per NiO, which is close to the theoretical capacity of nickel
oxide. Comparatively, dramatically fading capacity can be found for the nanoparticle sample from 620 mA h g-1 for the fifth cycle to 410 mA h g-1 the 10th cycle. The overall electrochemical process can be expressed as follows:


        In comparison with the NiO nanoparticles, the reversible capacity and cycleability of the oxide nanoplatelets have been much improved. The result indicates that the unique structure is beneficial to the improvement of electrochemical performance of nickel oxide due to the increased surface area and the porous structure, which facilitate the intercalation/deintercalation of lithium ions. A similar phenomenon was also found in the case of sheet-like V2O5 (798 mA h g-1)15 and board-like Ni(OH)2 (260 mA h g-1).4c The morphologically unique NiO nanoplatelets, as we expected, may give a new perspective for applications.
                                        Conclusions
              In summary, the work presented here reports a new method to fabricate single crystalline nickel oxide nanoplatelets with a unique porous structure on a large scale. The nickel oxide nanostructure was synthesized by thermal treatment of the hydroxide nanoplatelet precursor at 400 °C for 2 h in air. From the TEM results, the shape of the oxide nanoplatelets was sustained by the thermal decomposition of the hydroxide precursor. The surface of the oxide nanoplatelets is the {111} plane of the cubic NiO phase, and the adjacent edges with the angles of 120° should correspond to the {110} and {101} planes. ED patterns on different individual nanoplatelets were essentially the same, indicating the single crystalline nature of the NiO nanoplatelets. The result of the electrochemical test shows that the nanoplatelets exhibit an improved reversible capacity and cycleability in contrast with NiO nanoparticles. It suggests that the unique platelet-like porous structure is beneficial to the improvement of the electrochemical performance of the nickel oxide.

[ Last edited by carlosangel on 2010-2-27 at 16:38 ]
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sondwall

铁杆木虫 (著名写手)
哈哈，还没有人回复～～
第一次抢到了沙发，～～
我正好是学化学的，赶紧翻译ing~~~
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2楼2010-02-27 17:53:27
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xiaoqihu

铁杆木虫 (著名写手)
carlosangel(金币+100): 2010-02-28 15:12
高产率合成一氧化镍纳米板以及它们显著的电化学性能

摘要：我们成功的论证了一个新的大规模合成具有孔状结构的一氧化镍纳米板的方法。得到的这种氧化纳米板的性质经过了诸如x粉末衍射，透射电子显微镜，热重量分析，比表面积孔径测量，电化学测试等方法的检测。电化学测试结果表明，相对于平均大小9nm的微小纳米板，这种具有新颖形态的一氧化镍纳米板的电化学性能有进一步提高。这表明了独特的板状纳米结构能有效的提高氧化物的电化学性质。
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3楼2010-02-27 19:22:30
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carlosangel

新虫 (初入文坛)
引用回帖:
Originally posted by xiaoqihu at 2010-02-27 19:22:30:
高产率合成一氧化镍纳米板以及它们显著的电化学性能

摘要：我们成功的论证了一个新的大规模合成具有孔状结构的一氧化镍纳米板的方法。得到的这种氧化纳米板的性质经过了诸如x粉末衍射，透射电子显微镜，热重量 ...

好!继续！
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4楼2010-02-27 21:53:02
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xiaoqihu

铁杆木虫 (著名写手)
引论：

过渡金属的氧化物和氢氧化物，像钴，铁，镍等，由于他们的多领域潜在应用持续吸引专家们的目光。在这些过渡金属中，一氧化镍作为一个相对在氧化金属中具有p型的半导体性质，由于它稳定的band gap，一直被广泛的研究。一氧化镍是一个广泛的被应用于催化剂，锂电池电极，燃料电池，电色薄膜，电化超电容，dye-sensitized photocathodes.
由于在所有工业，科学领域中的突出表现，由于在纳米等级上的需求和在此级别性质上由于性状大小的改变特性，使得一氧化镍纳米级别的研究被逐渐重视。因此，目前有很多研究方法尝试制备纳米级别的一氧化镍，包括纳米颗粒，纳米环，纳米板，纳米缎带。在这片文章里，我们证明了一种新的大量合成一氧化镍纳米纤维晶体的研究方法，并且对其应用和已存在的特性上改进进行了研究。首先，单晶纳米板的氢氧化物是通过热分解氢氧化物前体被保留了下来，然后对其独特的氧化纳米结构电化学特性进行了测试研究。期望下一步能找到氧化过渡金属更广泛的潜在应用
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5楼2010-02-27 22:07:12
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xiaoqihu

铁杆木虫 (著名写手)
仪器实验条件我认为不用翻译了吧？你应该能看懂吧？

实验部分
所有的试剂均是试分析级别并且直接使用，无前处理工作。首先，氢氧化镍纳米板前体是通过热处理沉淀过程制备而来。操作为：10毫摩的新沉淀出的草酸镍加于20毫升的蒸馏水中，室温搅拌下加入20毫升0.4摩每升甲胺溶液.然后将混合物转移到60毫升的聚四氟乙烯封的高压釜中，封闭好，加热至120摄氏度并保持12小时。热处理以后，得到绿色的悬浮溶液。沉淀通过离心获得，沉淀用蒸馏水反复洗涤，60摄氏度下真空干燥。最后，将氢氧化物前体置于在400摄氏度下的空气中两小时，从而得到氧化产物。

晶体结构是通过x射线单晶衍射得到的。以下是各种仪器的实验条件
(XRD) using a Philips X’Pert Pro Super diffractometer with graphite monochromatized Cu KR radiation (λ= 1.541 78 A. High-resolution TEM images and selected-area electron diffraction (SAED) patterns were obtained on a JEOL-2010 transmission electron microscope at an acceleration voltage of 200 kV. Thermogravimetric analysis (TG) of the sample was carried out on a Shimadzu TA-50 thermal analyzer at a heating rate of 10 °C min-1 from room temperature to 600 °C in flowing air. N2 adsorption was determined by BET measurements using a NOVA-1000e surface analyzer.

氧化物的电化学性质测试是在聚四氟乙烯的样品池内进行的，阴极是氧化镍，乙炔黑，聚偏二氟乙烯的混合物，各重量比为85：10：5.金属锂作为阴极。电解液为1摩每升的 LiPF6 in a 1:1 mixture of ethylene carbonate (EC)/diethyl carbonate (DEC).The cell was galvanostatically cycled in the range of 3.0-0.5 V
平均9nm大小纳米级别的电化学特性同样也作了研究，制备方法是通过热分解草酸镍的纳米纤维。
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6楼2010-02-27 22:34:33
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xiaoqihu

铁杆木虫 (著名写手)
结果与讨论

图片一是单晶晶体结构图。图1a中所有的衍射峰可以被归置为六角形的 β-Ni-(OH)2的晶体。晶格参数为a =3.128 Å and c = 4.605Å；和已经报道的数值（ICDD-JCPDScard No. 14-0117)完全吻合。没有明显的杂质峰被检测到。图2是氢氧化物前提的TEM图形，通过图形可知是平均直径为50nm小板状的氢氧化物.大部分为不规则的六边形小板状。

TG分析结果表明，氢氧化物前体置于温度400度2小时是为了保证完全热分解 β-Ni(OH)2。图1b显示了一氧化镍粉末单晶衍射。所有的影像很好的和标准数据吻合(JCPDS card No. 47-1049)，可以被归置为面心立方体，拥有晶格参数为a = 4.175 Å（空间群Fm3hm），没有发现β-Ni(OH)2的峰，表明了其在400度下2小时被完全被分解掉了。TG测试也完全证明了这一点。宽的衍射峰表明了颗粒的细小。

图3是氧化物的TEM和高分辨TEM。从图3a，3b中可以观察到平均直径60nm有空的一氧化镍纳米板和通过在400度2小时条件下热分解氢氧化物纳米前体相同的板状形态。平均孔径为大约5nm.90%以上的产物均为板状结构。图3c是一典型的不规则的相邻角度为120度六角形纳米板的形状，实线所示。单独纳米板的放大图像是图3d。高分辨TEM显示其为完美的晶体结构。晶格参数为 1.4
Å, 以一氧化镍立方体为对比。插入的3f图是对应的SAED，ED图是通过坐标为 [-111]轴电子射线垂直照射与纳米板表面得到的。进一步的研究表明，纳米板的表面可以确定为一氧化镍立方体的『111』面，相邻角对应为{110}和{101}面，角度为120度。不同的单一纳米板的ED图是完全一样的，表明了此结构为自然的一氧化镍的纳米板单晶形式。

甲胺的有机碱环境条件对形成板状氢氧化物是极其重要的。如果甲胺被替换成其他碱，例如氨水，也能获得板状氢氧化物，但是等得到的纳米板厚度平均为前者的两倍，这对形成有空的氧化纳米板很不利。BET表面测量表现出一氧化镍纳米板的表面积为85m2g，相对于氢氧化镍纳米板的21有显著的增加。TEM检测氧化物的平均孔径为4.2。

氧化物纳米板的电化学检测是在室温下，电压范围为3.0到0.5伏，恒定电流为0.4.图4 是氧化物的纳米颗粒a和纳米板b的电压，放电量曲线图。对于纳米板，前20个循环的dp是1.5v，平均放电量为大概700ma，相对于理论的氧化镍电容1.95Li per NiO.然而，纳米颗粒动是成动态衰减的。从前50循环的600到后10循环的410。总的电化学过程如下表示


对比氧化镍的纳米颗粒，纳米板的可逆容量和循环性提高了很多。结论表明氧化镍的独特结构有利于电化学特性的提高，这得益于有孔和表面积增加。这又基于锂离子的置入或者去除。在片状V2O5的例子中相同的现象也被发现(798 mA h g-1)15 and board-like Ni(OH)2 (260 mA h g-1). 4c为我们所期盼的独特的氧化镍的纳米板，这将给我们新的应用前景
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7楼2010-02-27 23:50:02
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xiaoqihu

铁杆木虫 (著名写手)
game over

结论

这篇研究展现了新的关于大量独特的有孔氧化镍纳米板单晶的制备方法。氧化镍纳米结构是通过在400度空气中热处理氢氧化镍前体纳米板2小时制备而来。通过TEM得出了氧化镍纳米板的板状结构是由热分解氢氧化物前提纳米板得来的。氧化镍纳米板的表面是立方体氧化镍的111面，相邻角度为120度，所对应的角面为110，101.  ED表明不同单体纳米板本质上是一样的，这是氧化镍纳米板单晶的自然形态。电化学测试结果表明，相对于氧化镍纳米颗粒，氧化镍纳米板展现出了可逆容量和循环的提高，表明了独特有空的板状结构是有利于氧化镍的电化学特性的提高和改善。
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8楼2010-02-28 00:05:31
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