Structural defects working as active oxygen-reduction sites in partially oxidized Ta-carbonitride core-shell particles probed by using surface-sensitive conversion-electron-yield x-ray absorption spectroscopy

We analyzed the local structure of the surface Ta-oxide phase of TaCN/Ta(2)O(5) core-shell particles that have a high oxygen reduction activity by using surface-sensitive conversion-electron-yield x-ray absorption spectroscopy, suppressing the contribution from the TaCN cores. The radial structure analysis revealed that the catalytically-active Ta(2)O(5) phase in the TaCN/Ta(2)O(5) particle surface contains oxygen-vacancy defects with shorter Ta-O bonds leading to the slight expansion of the first Ta-O shell. Such oxygen defects are likely responsible for the oxygen reduction capability by creating electronically favorable oxygen adsorption sites and electron conduction pathways. (C) 2010 American Institute of Physics. [doi:10.1063/1.3430543]