CO₂ Reduction Characteristics at Pt_0.5Ru_0.5/C Cathode of H₂-CO₂ Polymer Electrolyte Fuel Cell (Supporting Information)

<div>CH₄ production by CO₂ reduction using a membrane electrode assembly containing a Pt/C electrocatalyst was recently demonstrated. Because this CO₂ reduction reaction occurs at approximately its theoretical electrode potential, it is possible to generate electric power as an H₂-CO₂ fuel cell by the reduction reaction occurring in combination with the H₂ oxidation reaction. However, the CH₄-generation reaction deactivated in a short time (∼5 min) due to the influence of the CO adsorbed on the Pt surface (CO_ads) as a reaction intermediate. In this study, we investigated the CO₂ reduction using a Pt_0.5Ru_0.5/C electrocatalyst in order to realize a continuous CH₄ production. As a result, steady CH₄ generation for more than 15 min with a faradaic efficiency of 12.0 % was observed at 0.22 V vs. RHE under a 4 vol% CO₂ atmosphere. In other words, an improved continuous CH₄ production was achieved by employing a Pt_0.5Ru_0.5/C electrocatalyst instead of Pt/C, and their faradaic efficiencies were equivalent. This result was obtained because the adsorption energy of CO_ads decreased due to the alloying of Pt and Ru based on the changes in the onset potential of the CH₄ production. In addition, power generation as an H₂-CO₂ polymer electrolyte fuel cell was observed while converting CO₂ to CH₄.</div>