Electronic Supplementary Information (ESI) available: [N2-sorption measurements performed with SBA-15 used as hard template for the synthesis of mesoporous oxides. Pdf data obtained from the characterization of MnCo2O4-δ, NiCo2O4-δ, Co3O4-δ, NiO materials. Voltammogram recorded in supporting electrolyte (KOH 0.1 M) under N2 atmosphere at a scan rate of 50 mV s -1 with mesoporous NiO catalyst at room temperature. Overlay of EIS bode plots for Co3O4-δ and NiCo2O4-δ at 1.800 V vs. RHE]. SeeAbstract: Co3O4-δ, MnCo2O4-δ, NiCo2O4-δ materials were synthesized using a nanocasting process consisting in replicating a SBA-15 hard template. Catalysts powders obtained were characterized using different physico-chemical techniques (X-ray scattering, transmission electron microscopy, N2 physisorption and X-ray photoelectron spectroscopy) in order to deeply characterize their morphostructural properties. Electrochemical measurements performed with cyclic voltammetry and electrochemical impedance spectroscopy techniques have shown that these catalysts were liable to surface modifications induced by the applied electrode potential. These surface structural modifications as well as their effect on the electroactivity of the catalyst towards the OER in alkaline medium are discussed. The activated NiCo2O4-δ material showed particularly excellent catalytic ability towards the OER in 0.1 M KOH electrolyte In this material Co (IV) is found to be the active species in the catalyst composition for the OER. It exhibits an overpotential as low as 390 mV at a current density of 10 mA cm -2 . This catalytic activity is especially high since the oxide laoding is only of 0.074 mg cm -2 . Furthermore, this anode catalyst showed high stability during an accelerated durability test of 1500 voltammetric cycles.Please do not adjust margins Please do not adjust margins region at three potential values (0.7; 0.8 and 1 V vs. RHE) for each catalyst.

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