New binary Mn and Cr mixed oxide electrocatalysts for the oxygen evolution reaction

• A novel, effective and non-precious OER catalyst of MnxCr1 − xO3/2 has been prepared for splitting water.
• The overpotential is comparable to the precious metal oxide IrOx.
• The MnxCr1 − xO3/2 catalyst has good stability in strong alkaline solution.

Transition metal mixed oxides of Mn and Cr with the nominal compositional formula MnxCr1 − xO1.5 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) were obtained by the thermal decomposition method. The powders were analyzed by SEM (scanning electron microscopy), XRD (X-ray diffraction) and XPS (X-ray photoelectron spectroscopy). The electrochemical properties of the MnxCr1 − xO1.5 electrodes for the OER (oxygen evolution reaction) in alkaline solution were evaluated by LSV (linear sweep voltammetry), staircase voltammetry and chronoamperometry. The results indicated that the mixed oxides were solid solutions of Mn2O3 (bixbyite) and Cr2O3 (eskolaite), and when x = 0.2, the catalyst had better catalytic activity in the OER process than did that of single Mn2O3 and Cr2O3. At the high potential region (1.0 V vs Ag/AgCl), the current density of the Mn0.2Cr0.8O1.5 electrode was ~ 80 times higher than that of Mn2O3 and ~ 9 times higher than Cr2O3, and its overpotential (η = 367.3 mV at a current density of 1.0 mA·cm− 2) was considerably lower than that of single Mn2O3 (η = 996.5 mV) and Cr2O3 (η = 648.5 mV) catalysts and was comparable to the precious metal oxide IrOx. The stability testing indicated that the mixed oxides had good stabilities in strong alkaline solution during the OER process.