Factors for improvements of catalytic activity for zirconium oxide-based oxygen-reduction electrocatalysts

摘要

Zirconium oxide based catalysts were evaluated as a non-precious cathode for polymer electrolyte fuel cells. Samples were prepared from zirconium carbonitrides under controlled oxygen partial pressure from 10~(-2) to 10~(-22) atm at 1000°C. Significant decrease in lattice parameter and Zr and O occupancy at around specific mass fraction revealed from high resolution XRD with Rietveld analysis, indicating formation of oxygen vacancies in monoclinic ZrO2. It is extrapolated from XRD, XPS, TOF-SIMS analyses that the oxide might be formed with the defects such as oxygen vacancy at both surface and bulk. Additionally, formation of the oxide with high concentration of the defects might be caused by behavior of the carbon on the surface. The oxygen vacancies could be active sites for the ORR, and increasing such oxygen-vacancy sites is one of the factors to improve the catalytic activity for the ORR in Zr- CNOs.