Even more recently, the mechanism of OER based on deprotonation was investigated on the (0001) facet of NiOOH using density functional theory (DFT), which provided further support for the role of deprotonation in OER activity . These calculations suggested that the deprotonation step is the potentialdetermining step with an overpotential of 0.44 V. It was discussed that this step also oxidizes Ni 3+ to Ni 4+ , while not changing the oxidation state of surface oxygen atoms .