Electrochemically induced surface modifications of mesoporous spinels (Co3O4−δ, MnCo2O4−δ, NiCo2O4−δ) as the origin of the OER activity and stability in alkaline medium†
Abstract
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 loading is only of 0.074 mg cm−2. Furthermore, this anode catalyst showed high stability during an accelerated durability test of 1500 voltammetric cycles.
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