An efficiently tuned d-orbital occupation of IrO by doping with Cu for enhancing the oxygen evolution reaction activity.

The oxygen evolution reaction (OER) has been regarded as a key half reaction for energy conversion technologies and requires high energy to create O[double bond, length as m-dash]O bonds. Transition metal oxides (TMOs) seem to be a promising and appealing solution to the challenge because of the diversity of their d-orbital states. We chose IrO as a model because it is universally accepted as a current state-of-the-art OER catalyst. In this study, copper-doped IrO, particularly CuIrO , is shown to significantly improve the OER activity in acidic, neutral and basic solutions compared to un-doped IrO. The substituted amount of Cu in IrO has a limit described by the CuIrO composition. We determined that the performance of CuIrO is due primarily to an increase in the Jahn-Teller effect in the CuO octahedra, and partially to oxygen defects in the lattice induced by the IrO octahedral geometric structure distortions, which enhance the lift degeneracy of the t and e orbitals, making the d orbital partially occupied. This phenomenon efficiently reduces the difference between Δ2 and Δ3 in the free energy from the density functional theoretical (DFT) calculations and can yield a lower theoretical overpotential comparable to that of IrO. The proposed method of doping with foreign elements to tune the electron occupation between the t and e orbital states of Ir creates an opportunity for designing effective OER catalysts using the TMO groups.