Insight the effect of surface Co cations on the electrocatalytic oxygen evolution properties of cobaltite spinels

In this paper, the electrocatalytic performance of cobaltite spinels for oxygen evolution reaction (OER) in alkaline electrolysis is studied. Cobaltites MxCo3-xO4 (M= Ni, Cu, Zn, Mn; x = 1 or 0.9) are synthesized by the coprecipitation method and characterized for the OER performance. Cyclic voltammetric measurement confirms that the cobaltites exhibit different redox characteristic for Co cation couples. NiCo2O4 and MnCo2O4 show the redox couple of Co(III)/Co(II) during OER, while for ZnCo2O4 and Cu0.9Co2.1O4 are Co(IV)/Co(III). OER measurement reveals that all these cobaltite spinel electrodes show better performance than metal Ni electrode. And ZnCo2O4 shows the best performance for OER with the highest current density of 205mAcm−2 at potential of 0.7 V. XPS result verifies that the cobaltites have the different surface Co cations distribution. The analysis discovers that the amount of the surface Co cations occupying the octahedral sites in spinel is crucial for OER performance.