A’–B Intersite Cooperation-Enhanced Water Splitting in Quadruple Perovskite Oxide CaCu3Ir4O12

Abstract

Developing highly efficient electrochemical catalysts and exploring the basic mechanisms for the oxygen evolution reaction (OER) are key issues for the large-scale commercialization of environmentally friendly electrolytic hydrogen energy. Compared with a simple ABO3 perovskite, the A-site-ordered quadruple structure AA’3B4O12 shows enhanced OER activity, but the underlying mechanisms remain unknown. Herein, we find that the quadruple perovskite oxide CaCu3Ir4O12 has stable and superior electrochemical activity with a very low overpotential of 252 mV to achieve the current density of 10 mA·cm–2 in alkaline solution. Operando X-ray absorption spectroscopy reveals that the B-site Ir is an OER active site with a variable valence state from the initial Ir4+ approach to Ir5+, while the A’-site Cu is inactive with a constant valence state during the OER process. Density functional theory calculations demonstrate that the A’–B intersite cooperation synergistically enhances OER activity via the corner-sharing Cu–O–Ir framework owing to the strong 3d–2p–5d orbital hybridizations, regardless of the inactive Cu site. In the structural constitution of CaCu3Ir4O12, a small Cu–O–Ir bond angle (110.7°) forms. The special orbital symmetry as well as the delicate 3d–5d levels enhance the orbital overlap and therefore promote the charge transfer, favoring the superior OER activity of CaCu3Ir4O12.