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Article

Abstract

The electrochemical selectivity of a Ca2Ru2O7−y pyrochlore 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 Ca2Ru2O7−y was used as the cathode catalyst, compared to Pt/C. Carbonate selectivity for Pt/C was 1.78, while for Ca2Ru2O7−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.

Available for download on Friday, November 29, 2019

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