Reduction of CO2 to CO at Cu–ceria-gadolinia (CGO) cathode in solid oxide electrolyser

The feasibility was investigated of using a Cu/CGO cathode for CO2 reduction to CO in a high temperature solid oxide electrolyser (CO2–CO, Cu/CGO|YSZ|YSZ/LSM|LSM, ambient air). An adherent layer of porous Cu/CGO electrode on YSZ electrolyte was achieved by sintering Cu/CGO paste at 1,000 °C for 5 h. Comparable performance was obtained with Ni/YSZ and Cu/CGO cathodes for CO2 reduction at 750 °C and a 50:50 CO2–CO feed; CO oxidation rates were faster than CO2 reduction rates. Ohmic and polarisation resistances of the Cu/CGO electrode all decreased with decreasing CO2:CO feed ratio. In the electrolytic mode, 100 % current efficiency for CO2 reduction to CO was achieved on the Cu/CGO cathode at potential differences up to 1.5 V, above which the electronic conductivity of the YSZ electrolyte increased, causing a loss in effective current efficiency. Further increase in potential difference to ca. >2.3 V caused irreversible damage to the YSZ electrolyte due to its partial decomposition. No significant performance degradation, Cu sintering/migration, carbon deposition or electrode delamination was evident during 2 h of operating the electrolyser at 1.85 V and 750 °C for CO2 reduction with a Cu/CGO cathode.