Highly active NiFeO x electrocatalysts for the oxygen evolution reaction (OER) suffer gradual deactivation with time owingtothe loss of Fe species from the active sites into solution during catalysis.T he anodic deposition of aC eO x layer prevents the loss of such Fe species from the OER catalysts, achieving ah ighly stable performance.T he CeO x layer does not affect the OER activity of the catalyst underneath but exhibits unique permselectivity,a llowing the permeation of OH À and O 2 through while preventing the diffusion of redox ions through the layer to function as as elective O 2 -evolving electrode.T he use of such ap ermselective protective layer provides an ew strategy for improving the durability of electrocatalysts.Hydrogen is an energy carrier that can effectively store intermittent energy generated by renewable energy sources, such as solar and wind power. Many techniques,such as water electrolysis and photoelectrochemical water splitting, have been studied for the generation of hydrogen and oxygen from water. Unlike the hydrogen evolution reaction (HER) conducted on the cathodic side,t he anodic oxygen evolution reaction (OER) is ak inetically sluggish reaction, requiring as ubstantial overpotential. Highly active,d urable,a nd costeffective electrocatalysts for OER are desired for the development of an efficient water splitting device.NiFeO x is one of the most active electrocatalysts for OER in alkaline conditions,and while it is known that Fe plays acritical role in the improved activity, [1] the origin of the enhancement of the OER kinetics by Fe doping is still under debate.A lthough many studies have been devoted to decreasing the overpotential via the development of an LDH structure, [2]