Surface Engineering in MgCo₂O₄ Spinel Oxide for an Improved Oxygen Evolution Reaction

Spinel-type oxides exhibit great potential for the electrocatalytic oxygen evolution reaction (OER) due to their variable surficial composition and electronic structure. Herein, taking MgCo2O4 as a prototype, we put forward a surface engineering procedure to tailor the surface composition and valence state of cobalt ions for enhancing the OER performance. We discovered that the calcination temperature can finely tailor the ratio of Co/Mg and Co3+/Co2+ on the surface of MgCo2O4. MgCo2O4 with the maximum ratio of Co3+/Co2+ gives a current density of 10 mA cm–2 at a small overpotential of 283 mV. Such an overpotential is significantly lower than that of most cobalt-based spinel oxides ever reported. X-ray photoelectron spectra demonstrate that increasing the ratio of Co3+/Co2+ plays key roles in improving the OER performance. This work furnishes an instructive idea in pursuit of spinel-type oxides with high OER catalytic activity and stability by surface engineering