A Design Strategy for Highly Active Oxide Electrocatalysts by Incorporation of Oxygen‐Vacancies
Narayan Acharya, Surendra B. Karki, Livia Giordano, Farshid Ramezanipour
Abstract
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, LaCoO 3 was investigated, where the incorporation of oxygen‐vacancies led to La 3 Co 3 O 8 (LaCoO 2.67 ), 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 La 3 Co 3 O 8 (LaCoO 2.67 ) showed a remarkable enhancement of electrocatalytic properties over the parent compound LaCoO 3 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 La 3 Co 3 O 8 and higher than LaCoO 3 , 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 La 3 Co 3 O 8 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.