Development of CaMn_1-xRu_xO_3-y (x = 0 and 0.15) oxygen reduction catalysts for use in low temperature electrochemical devices containing alkaline electrolytes: ex situ testing using the rotating ring-disk electrode voltammetry method

Various inorganic solid state catalysts are of interest for use as cathode catalysts in low temperature alkaline fuel cells including alkaline polymer electrolyte fuel cells. This ex situ study compares the oxygen reduction reaction in aqueous KOH (1 mol dm⁻³) electrolyte on solid state and sol–gel synthesised CaMn_1−xRu_xO₃ (x = 0 and 0.15) catalysts along with fuel-cell-grade Pt-based benchmark catalysts. The inclusion of Ru (e.g. in the CaMn_0.85Ru_0.15O₃ examples) led to enhanced electronic conductivities compared to the Ru free exemplars. Rotating ring disk electrode hydrodynamic voltammetry was successfully used to determine the electron transfer numbers and hydrogen peroxide production yield for each catalyst. The electron transfer numbers of a number of the catalysts promisingly approach n = 4 (the same as for the platinum benchmarks). However, the on-set potentials of the CaMn_1−xRu_xO₃ (x = 0 and 0.15) catalysts were less than that of the Pt-based benchmarks and they also degraded in the alkaline conditions used (with a further decrease in onset potentials on degradation): the results from the study lead to the hypothesis that the degradation is related to the electrochemically generated peroxide.