Enhancement of Electrocatalytic Activity as a Function of Structural Order in Perovskite Oxides
Surendra B. Karki, Ram Krishna Hona, Mingquan Yu, Farshid Ramezanipour
Abstract
Electrocatalytic splitting of water is a promising method of hydrogen generation. Here, we report an enhanced electrocatalytic performance for water electrolysis, achieved through a progressive increase in the ordering of oxygen vacancies in the structural network of oxides. In transition from Sr2FeCoO6−δ (disordered) to CaSrFeCoO6−δ (ordered) and Ca2FeCoO6−δ (highly ordered), the change in the average ionic radius of the A-site metals leads to an increase in the concentration and ordering of oxygen vacancies, resulting in a progressive enhancement of the electrocatalytic activity for both cathodic and anodic half-reactions of water splitting, i.e., hydrogen-evolution (HER) and oxygen-evolution (OER) reactions. The OER electrocatalysis is particularly important, as it is considered the bottleneck for water electrolysis. These electrocatalysts show better activity than the precious metal catalyst RuO2. In contrast to most bifunctional catalysts reported to date, these catalysts can be used in bulk form, without the need for nanofabrication, composite formation, or any additional processing. Density functional theory calculations indicate that the vacancy order leads to a shift of the electronic bands toward the Fermi level. We propose that the ordering of oxygen vacancies can be used as a handle for the design of highly active electrocatalysts.