Preparation of electrocatalysts with unique CO-tolerance and their application to polymer electrolyte fuel cells

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The objectives of this research are to clarify why Pt-Ni alloy nanoparticle catalysts, which are prepared by casting PtC16^2. aqueous solutions on a Ni substrate, have remarkable activity for CO oxidation and evaluate the activity for hydrogen oxidation reaction (HOR) on CO-preadsorbed Pt-Ni catalysts. The results obtained in this study are shown as follows.1) The oxidation of CO on a Ni electrode was analyzed by EQCM. Anodic dissoloution of CO-adsorbed Ni started with the oxidation of adsorbed CO, and the initiation potential of Ni dissolution shifted ca. 300 mV more positive than bare Ni. The dissolution amount in the former was much smaller than that in the latter. The potential for the initiation of Ni dissolution depended on the concentration of sulfate. These results clearly indicate that the adsorption of CO on Ni effectively suppress the anodic dissolution of Ni.2) Cyclic voltammograms of hydrogen evolution reaction (HOR) at the Pt-Ni/Ni electrodes with and without adsorbed CO indicated the following results. Current for HOR was observed even at CO-adsorbed Pt-Ni/Ni electrode and depended on temperature. In each case a Tafel slope was 30 mV dec-^1 irrespective of CO adsorption, suggesting that HOR at the Pt-Ni/Ni electrodes with and without adsorbed CO follows the Tafel-Volmer mechanism. The Pt-Ni/Ni electrodes can maintain the capability for hydrogen oxidation even though CO adsorbed on them.3) The current for HOR at the Pt-Ni/Ni electrode increased with temperature like the Pt electrode. But the former showed relatively high current for HOR even after adsorbing CO while the latter did not. Assuming that the HOR proceeds in two-electron oxidation mechanism, the CO coverage of the Pt:NI/Ni electrode was ca. 40% at 25℃ and ca. 18% at 60℃, indicating that the CO-tolerance was increased with temperature.