Theoretical studies on the mechanism of oxygen reduction reaction on clean and O-substituted Ta3N5(100) surfaces

Abstract

The reaction mechanism of oxygen reduction reaction (ORR) on Ta₃N₅(100) surfaces was examined theoretically. In particular, the effects of O-substitution on the catalytic activity have been discussed. First, the adsorption energy and geometry of an oxygen molecule adsorbed on a clean and an O-substituted Ta₃N₅(100) surface were calculated. Energy diagrams for 2-electron and 4-electron reactions on clean and O-substituted Ta₃N₅(100) surfaces were then examined. The results show that the adsorption energy of an oxygen molecule on the clean Ta₃N₅(100) surface is almost zero and the oxygen molecule is easier to adsorb on the O-substituted surface. However, OH and H₂O adsorb strongly on the O-substituted surfaces so that their desorption can be the rate-determining step. To improve the ORR activity, both O₂ and OH adsorption energies should be tuned. By analysis of the energy level of adsorbates and Ta₃N₅ O-substituted surface, the impurity state of Ta₃N₅ is found to be the key descriptor for the adsorption energy. Therefore, the ORR activity can be controlled by changing the energy of the impurity state.