Tuning of eg electron occupancy of MnCo2O4 spinel for oxygen evolution reaction by partial substitution of Co by Fe at octahedral sites

To study the effect of partial Co substitution by Fe in the B-site of MnCo2O4 spinel on its physicochemical and electrochemical properties, a series of MnCo2-xFexO4 powders (x = 0.125; 0.250; 0.500; 0.750; 1.000) were synthesized by means of the sol-gel method. The produced powders were characterized by powder X-ray diffraction (pXRD), scanning and transmission electron microscopy (SEM & TEM) coupled with energy dispersive spectroscopy (EDS), X-ray photoelectron and absorption spectroscopy (XPS & XAS), Fourier transformed infrared spectroscopy (FTIR), and inductively coupled plasma optical emission spectroscopy (ICP-OES). The electrocatalytic activity towards oxygen evolution reaction (OER) was evaluated in an alkaline environment (0.1 M KOH). From our findings, the activity increased with the addition of Fe up to x = 0.5, characterized by a decrease of overpotential at 10 mA cm−2GEO from 406 mV for MnCo2O4 to 376 mV for MnCo1·5Fe0·5O4, with a corresponding 44 mV dec−1 Tafel slope. It was identified that the OER-specific activity exhibits a volcano-type shape as a function of the eg occupancy at octahedral sites tuned by Co substitution with Fe.