Highly selective methane generation by carbon dioxide electroreduction on carbon-supported platinum catalyst in polymer electrolyte fuel cell

The objective of this study was to decrease the large overpotential encountered at the Cu and Au electrodes used for the CO2 reduction reaction (CO2RR) to realize a continuous reaction near the theoretical electrode potential. The CO2RR at the theoretical potential, when possible, could enable the generation of electric power in a fuel cell by combination with the hydrogen oxidation reaction (HOR). We employed a polymer electrolyte cell incorporating Pt/C as an electrocatalyst to electrochemically reduce CO2 with a small overpotential. However, the COads generated by CO2 reduction poisons the subsequent reaction. Our current strategy was designed to avoid this poisoning. First, by feeding diluted CO2 to the polymer electrolyte cell, the surface concentration of COads on the Pt catalyst was suppressed. Second, the reduction reaction was found to occur at 0.1–0.2 V vs RHE to selectively produce CH4 under a diluted CO2 feed. Subsequently, optimized operation with 4 vol% CO2 feeding at 0.16 V vs RHE enabled selective and continuous CH4 production at a faradaic efficiency of 12.3%. Next, by choosing an HOR as the counter electrode reaction, an H2–CO2 fuel cell was realized for simultaneously generating continuous electric power and CH4 as a product. Consequently, an optimized H2–CO2 fuel cell operation procedure has been realized to reduce CO2 and obtain CH4 during power generation. •Polymer electrolyte cell with Pt/C electrocatalyst was used for CO2 reduction.•CO2 was reduced to CH4 selectively with a negligible overpotential.•Faradaic efficiency of 12.3% for CH4 generation was achieved.•H2–CO2 fuel cell generating both electric power and CH4 was realized.