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

Transition metal mixed oxides of Mn and Cr with the nominal compositional formula Mn x Cr 1   −   x O 1.5 ( 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 Mn x Cr 1   −   x O 1.5 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 Mn 2 O 3 (bixbyite) and Cr 2 O 3 (eskolaite), and when x   =   0.2, the catalyst had better catalytic activity in the OER process than did that of single Mn 2 O 3 and Cr 2 O 3 . At the high potential region (1.0   V vs Ag/AgCl), the current density of the Mn 0.2 Cr 0.8 O 1.5 electrode was ~   80 times higher than that of Mn 2 O 3 and ~   9 times higher than Cr 2 O 3 , and its overpotential ( η   =   367.3   mV at a current density of 1.0   mA·cm −   2 ) was considerably lower than that of single Mn 2 O 3 ( η   =   996.5   mV) and Cr 2 O 3 ( η   =   648.5   mV) catalysts and was comparable to the precious metal oxide IrO x . The stability testing indicated that the mixed oxides had good stabilities in strong alkaline solution during the OER process.