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5. Analysis. Finely ground powders were examined with a Rigaku Ultima VI powder X-ray diff -ractometer (PXRD) with Cu K radiation (K¦Á1, ¦Ë = 1.5406 Å and K¦Á2, ¦Ë = 1.5444 Å . Crystal structures of the oxide and the resulting nitride were confirmed by PXRD pro files using the GSAS package. The nitride crystalline domain size can be estimated from a Rietveld fit of the Lorentzian function, as discussed previously in the synthesis of metal (oxy)nitrides from Zn-containing oxides. 34 Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) were performed with a LEO-1550 field emission SEM (FSEM). Approximately 2 mg of CrN was dispersed in 2 mL of ethanol. The solution was sonicated for 30 min, and then one drop of the solution was transferred by glass pipet onto a TEM copper grid (3.05 mm holey carbon, Sigma-Aldrich). Transmission electronmicroscopy (TEM) was performed with a FEI T12 Spirit TEM STEM. Nitrogen adsorption/desorption isotherms were measured at −196 ¡ãC using a Micromeritics ASAP 2020 system. The samples were degassed at 200 ¡ãC for 24 h on a vacuum line. Elemental analyses of nitrogen and oxygen content of the nitride samples were done with a LECO TC-600 analyzer using the inert gas fusion method. Nitrogen was detected as N 2 by thermal conductivity, and oxygen was detected as CO 2 by infrared detection. The apparatus was calibrated using Leco standard oxides; Si 2 N 2 O and TaN were used as nitrogen standards. 34 A four-point probe measurement of conductivity of the compressed powders at a relatively low pressure of 35 bar was used to estimate the electrical conductivity of compressed mesoporous CrN powder. 12. A simple method for synthesizing high surface area mesoporous CrN by the ammonolysis of bulk K2Cr2O7 has been presented. The proposed mechanism involves phase separation of K salts from CrN and a condensation of K and O vacancies to form mesopores. The CrN synthesized was electrochemically stable up to 1.2 V. A mesoporous CrN supported Pt catalyst (Pt/CrN) showed a greater intrinsic catalytic surface area, greater electrocatalytic activity, slower deterioration rate, and greater steady-state current than a conventional Pt/C catalyst toward methanol electrooxidation. This improved performance is mainly due to the high corrosion resistance and high conductivity of the mesoporous CrN support, coupled with a synergistic behavior between Pt and CrN that allows faster oxidation of CO produced by methanol oxidation. It follows that mesoporous CrN should be further studied as a high performance catalyst support that could potentially replace standard carbon catalyst supports in DMFCs. |
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. Crystal structures of the oxide and the resulting nitride were confirmed by PXRD pro files using the GSAS package. The nitride crystalline domain size can be estimated from a Rietveld fit of the Lorentzian function, as discussed previously in the synthesis of metal (oxy)nitrides from Zn-containing oxides. 34 Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) were performed with a LEO-1550 field emission SEM (FSEM). Approximately 2 mg of CrN was dispersed in 2 mL of ethanol. The solution was sonicated for 30 min, and then one drop of the solution was transferred by glass pipet onto a TEM copper grid (3.05 mm holey carbon, Sigma-Aldrich). Transmission electronmicroscopy (TEM) was performed with a FEI T12 Spirit TEM STEM. Nitrogen adsorption/desorption isotherms were measured at −196 ¡ãC using a Micromeritics ASAP 2020 system. The samples were degassed at 200 ¡ãC for 24 h on a vacuum line. Elemental analyses of nitrogen and oxygen content of the nitride samples were done with a LECO TC-600 analyzer using the inert gas fusion method. Nitrogen was detected as N 2 by thermal conductivity, and oxygen was detected as CO 2 by infrared detection. The apparatus was calibrated using Leco standard oxides; Si 2 N 2 O and TaN were used as nitrogen standards. 34 A four-point probe measurement of conductivity of the compressed powders at a relatively low pressure of 35 bar was used to estimate the electrical conductivity of compressed mesoporous CrN powder.
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