The specific activity (Js), which is the current density averaged by the electrochemical surface area, is a parameter that is complementary to TOF in evaluating the intrinsic activity of electrocatalysts . To make a direct comparison, the specific activities of our NiOx-Fe catalyst and NiFeOx deposited on the same supports (NF and GC) were measured (Supplementary Methods). It was previously reported that NiFeOx had the highest specific activity among various transition metal oxides . On both electrodes, our catalyst has 3-4 times higher specific activity than NiFeOx (Fig. , Table and Supplementary Table ). The specific activity on GC is higher than on NF for both catalysts because electrochemical surface areas correspond only to those of the catalysts due to the GC's flat surface, while on NF the areas correspond to those of the porous NF electrodes. The values on GC are therefore representative of the true activity of the catalysts. For the NiFeOx catalyst, our value is similar to those determined in the literature , confirming that the NiFeOx catalyst used in the direct comparison exhibits the same activity as the state-of-the-art samples. The intrinsic activity of the bifunctional NiOx-Fe catalysts is therefore superior to all known catalysts for which an intrinsic activity have been reported.