According to computations, the availability of -FeOOH sites, with an equilibrium potential of about 1.2 V for the formation of Fe=O, is a pre-requisite for the proposed bifunctional catalysis. In NiFeOx, the Fe ions are incorporated into an extended lattice of -NiOOH. The resulting structural and electronic change shifts the Fe=O formation potential to about 1.6 V 24 and as a consequence, the theoretical overpotential is 0.4 V with or without a suitable hydrogen acceptor.