Revealing the bifunction mechanism of LaCoO3 as electrocatalyst: Oxygen vacancies effect and synergistic reaction process

Abstract

Bifunctional perovskite catalysts with both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activity have potential applications in metal-air batteries and regenerative fuel cells etc. Elucidating the microscopic mechanism of the perovskite bifunctionality is of great scientific significance. Here, we studied the effects of oxygen vacancy (VO) on OER and ORR reaction processes on the LaCoO3 surface based on the first-principles calculations. The results reveal the linear relationship between OER overpotential and the d‐band center of Co active site at the surface, which relates to the covalent component of the bond between the active sites and the oxygen atom in the intermediates. The O2 desorption is linearly related to the distance between the d‐band center of Co active site and the p-band center of the oxygen atom in the O2 intermediate. When VO is located at the subsurface, d‐band center of the Co active site and the covalent component of the bond between Co and O increase, and the OER activity of the adsorbate evolution mechanism is significantly enhanced with an overpotential of about 0.50 V. However, the desorption of OH intermediate is too difficult without VO or the adsorption for O2 with VO is too weak for the reverse ORR reaction to occur. Therefore, the synergistic reaction mechanism involving Co and the adjacent surface VO is proposed for the ORR process with an overpotential of 0.31 V. The reverse OER reaction pathway with the lattice oxygen participation mechanism has an overpotential of 0.25 V, whereas the kinetics are limited because of the difficult desorption of O2. Therefore, OER and ORR take a non-reverse reaction pathway, and the results can well explain the microscopic mechanism by which LaCoO3 has excellent intrinsic ORR activity and VO enhances the LaCoO3 bifunctionality, and provide theoretical basis for understanding the microscopic mechanism of bifunctional materials.