Abstract
Vulcan XC-72R carbon-supported IrxSey chalcogenide catalysts with different Se/Ir atomic composition were synthesized via a microwave-assisted polyol process using H2IrCl6 and Na2SeO3 as the Ir and Se precursors. IrxSey chalcogenide catalysts were characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The data were discussed with respect to the Se-free carbon-supported Ir nanoparticles prepared by the same microwave-assisted polyol process. The XRD results revealed that IrxSey chalcogenide catalysts showed characteristic reflections of cubic metallic iridium, and the average particle size increased with the increase of Se content in the chalcogenide catalysts. TEM images indicated that IrxSey chalcogenide catalysts were well dispersed on the surface of the carbon support with a narrow particle size distribution when y/x ≤ 1/3. When y = x, because of the particle agglomeration, we were not able to build particle size distribution and calculate the average particle size for Ir50Se50/C catalyst. Cyclic voltammogram (CV), rotating disk electrode (RDE) and single-cell measurements were conducted to evaluate the electrocatalytic activity of IrxSey chalcogenide catalysts. The CV results suggested that Se covered some surface area of Ir particles, and also, the surface properties of Ir particles were changed after Se modification. The RDE measurements were carried out with the absence/presence of methanol. In the absence of methanol, IrxSey/C catalysts showed a comparable oxygen reduction reaction (ORR) activity with Pt/C catalyst. However, in the presence of methanol, IrxSey/C catalysts showed a better ORR activity than Pt/C catalyst. The performance of the membrane electrode assembly (MEA) prepared with the most active Ir85Se15/C as the cathode catalyst in a single proton exchange membrane fuel cell (PEMFC) was also tested and achieved a maximum power density of 500 mW cm-2 at the current density of 1500 mA cm-2.
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