A Design Strategy for Highly Active Oxide Electrocatalysts by Incorporation of Oxygen-Vacancies.

Abstract

Using both density functional theory (DFT+U) simulations and experiments, we show that the incorporation of an ordered array of oxygen-vacancies in a perovskite oxide can lead to enhancement of the electrocatalytic activity for the oxygen-evolution reaction (OER). As a benchmark, LaCoO3 was investigated, where the incorporation of oxygen-vacancies led to La3Co3O8 (LaCoO2.67), featuring a structural transformation. DFT+U simulations demonstrated the effect of oxygen-vacancies on lowering the potential required to achieve negative Gibbs Free Energy for all steps of the OER mechanism. This was also confirmed by experiments, where the vacancy-ordered catalyst La3Co3O8 (LaCoO2.67) showed a remarkable enhancement of electrocatalytic properties over the parent compound LaCoO3 that lacked vacancies. We also synthesized and studied an intermediate system, with a smaller degree of oxygen-vacancies, which showed intermediate electrocatalytic activity, lower than La3Co3O8 and higher than LaCoO3, confirming the expected trend and the impact of oxygen-vacancies. Furthermore, we employed additional DFT+U calculations to simulate a hypothetical material with the same formula as La3Co3O8 but without the vacancy-order. We found that the gap between centers of Co d and O p bands, which is considered an OER descriptor, would be significantly greater for a hypothetical disordered material compared to an ordered system.