Catalytic Activity for Oxygen Reduction Reaction on Tantalum Oxide-Based Compounds (2) Active Sites of TaON Thin Film Catalysts and Role of Carbon

We analyzed TaCxNyOz and TaNxOy thin film catalysts prepared by reactive sputtering under Ar, N-2 and O-2 mixture with TaC or TaN target to reveal a correlation between oxygen reduction activity and physico-chemical properties of the films. XPS and Raman spectroscopy indicated that the graphite and amorphous carbon existed on the surface and grain boundary of the TaCxNyOz. Deposited carbon provides electrical condition paths that are necessary for oxygen reduction reaction (ORR) to be effectively occurred. X ray absorption spectroscopy analysis revealed that both the TaCxNyOz and TaNxOy had some oxygen and/or nitrogen defects compared to the ideal TaON, providing oxygen adsorption sites. Because the TaCxNyOz had both oxygen and/or nitrogen defects as oxygen adsorption sites and deposited carbon as electrical condition paths, the TaCxNyOz showed higher ORR activity than the TaNxOy.