Activity of perovskite La1−xSrxMnO3 catalysts towards oxygen reduction in alkaline electrolytes

The behaviour of the perovskite-based series of compounds La1−xSrxMnO3 (where x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) towards oxygen reduction in an ambient temperature alkaline 1 M KOH electrolyte is presented. Within this series, the intermediate compound La0.4Sr0.6MnO3 exhibits the greatest catalytic activity, approaching that of the considerably more expensive fuel cell grade Pt-black examined under the same conditions. The origin of this activity is discussed in terms of material structure and morphology, which exists in the structural transition region between cubic LaMnO3 and hexagonal SrMnO3. The small crystallite size and relatively large BET surface area of this material reflect this high level of structural disorder. Furthermore, these features enable this compound to exhibit the greatest proportion of direct four-electron oxygen reduction (preferred) compared to the less efficient two-electron reduction to peroxide.