Elevated temperature and pressure driven ampere-level CO2 electroreduction to CO in a membrane electrode assembly electrolyzer†

Achieving high selectivity for carbon monoxide (CO) in the electrochemical reduction of carbon dioxide (CO₂) at industrially relevant current densities, particularly using dilute CO₂ feedstocks, remains a significant challenge. Herein, we demonstrate that combining elevated temperature and CO₂ pressure substantially enhances CO production in a membrane electrode assembly (MEA) electrolyzer using commercially available silver nanoparticles. Elevated CO₂ pressures increase CO₂ concentration and reduce the diffusion layer, counteracting the reduced CO₂ solubility in water and enhanced wetting of catalyst layer caused by high temperature. The synergy of high pressure and temperature ensures high CO₂ flux to the catalyst surface while leveraging elevated temperatures to accelerate reaction kinetics. Therefore, the pressurized and heated CO₂ electrolyzer achieves an FE_CO of 92% at a high current density of 2 A cm⁻² and a low cell voltage of 3.8 V under 10 bar and 80 °C when using 0.1 M KHCO₃ as the anolyte. Even when using pure water as the anolyte, the system maintains a FE_CO value of 90% at 300 mA cm⁻² and a cell voltage of 3.6 V. Furthermore, the system demonstrates exceptional performance with dilute 10 vol% CO₂ feedstocks, achieving a FE_CO of 96% at 100 mA cm⁻² and 2.4 V. These findings underscore the potential of combined temperature and pressure optimization to overcome mass transport limitations and enhance reaction kinetics, offering a viable pathway for scaling up CO₂ electrolyzers for industrial applications.