Carbonate Selective Ca2Ru2O7-yPyrochiore Enabling Room Temperature Carbonate Fuel Cells.

The electrochemical selectivity of a Ca₂Ru₂O_7-y pyrochiore catalyst towards carbonate formation was investigated and compared to platinum. During constant current operation, an increase in CO₂ content was observed at the anode effluent when Ca₂Ru₂O_7-y was used as the cathode catalyst, compared to Pt/C. Carbonate selectivity for Pt/C was 1.78, while for Ca₂Ru₂O_7-y it was 7.33, a 4.1X increase, which confirmed the preferential formation of carbonate on the pyrochlore. This elevated selectivity was attributed to the high surface basicity of the pyrochlore catalyst, which led to preferential CO₂ adsorption. During constant voltage operation, a 134% CO₂ concentration increase was measured at the anode effluent when 10% CO₂ was supplied to the cathode inlet. Optimal fuel cell performance on the carbonate cycle was obtained with a 90% O₂/10% CO₂ cathode concentration, where maximum currents where 4X compared to operation with no CO₂. Higher CO₂ concentrations were matched with a gradual decrease in performance. This was attributed to a relatively low electrochemical activity, which combined with high surface basicity, led to O₂ Site blocking. Thin-film electrode experiments showed excellent electrochemical stability on the oxygen reduction region. An increase in the current and a positive shift in the half-wave potential were observed when CO₂ was added to the electrolyte in ex-situ three electrode experiments. [ABSTRACT FROM AUTHOR]