Bifunctional Water-Splitting Electrocatalysis Achieved by Defect Order in LaA₂Fe₃O₈ (A = Ca, Sr)

We report the utilization of defect order for development of a bifunctional oxide electrocatalyst. This structure–activity relationship is demonstrated through a disorder–order transformation in LaA₂Fe₃O₈ (A = Ca, Sr). The defect-ordered oxide, LaCa₂Fe₃O₈, shows electrocatalytic activity for oxygen evolution reaction, on par with that of the state-of-the-art precious metal catalyst RuO₂. In addition, it is capable of catalyzing the other half-reaction of water-splitting, namely the hydrogen evolution reaction. Importantly, it is an iron-based catalyst and can be used as a single phase bulk material. The most important aspect of this work is the pronounced impact of defect order on the electrocatalytic properties of oxides.