Interfacial recharging behavior of mixed Co, Mn-based perovskite oxides

We report the voltammetric and soft X-ray absorption spectroscopy (XAS) data for two series of perovskite oxides, namely La 1− y Sr y Mn 0.5 Co 0.5 O 3− δ with a constant Mn:Co ratio and variable extent of Sr doping, and Sr 0.5 Gd 0.5 Mn x Co 1− x O 3− δ perovskite oxides with a constant Sr content but variable extent of the Co doping. The essential differences in the values and scan rate dependences of the total charges observed between the studied materials in alkaline solutions in the potential regions of their stability are interpreted on the basis of separation of the ‘fast’ and ‘slow’ recharging components. Our analysis of the total charge is based on two approaches, the first proposed by Trasatti, the second by Conway. The ‘slow’ charge is assigned to the oxygen intercalation in sub-surface oxide layers. We demonstrate correlations of the ‘fast’ and the ‘slow’ recharging components with the electronic state of Mn, Co and O determined from spectroscopic data. We also present the arguments in favor of possible contribution of the interfacial oxygen vacancies to the ‘fast’ interfacial recharging. These findings may be useful for understanding correlations of the composition and stoichiometry of the oxides on the one hand, and their electrocatalytic activity on the other.