The oxygen evolution reaction (OER) on metal oxide surfaces offers a promising avenue for the development of materials for clean-energy and environmental applications. This O-O dimerization reaction, which is governed by complex electron transfer processes, is key to the performance of technological devices such as water-splitting devices , fuel cells , rechargeable metal-air batteries and the storage of energy in lithium-ion battery materials . The current understanding of the OER mechanism suggests that four sequential concerted proton-electron transfer steps (2 H 2 O → O 2 + 4 H + + 4 e -) yield molecular oxygen from water , resulting in a pH-independent activity on the reversible hydrogen electrode (RHE) scale . In this mechanism, high OER activities can be achieved by tuning the binding strength of reaction intermediates on oxide surfaces , correlating with electronic structure parameters such as the e g occupancy of surface transitionmetal ions . However, recent observations have called into question this established mechanism, proposing instead the involvement of lattice oxygen redox chemistry , non-concerted protonelectron transfers and pH-dependent OER activity .