Insights into zero-gap CO2 electrolysis at elevated temperatures†

Renewable-powered CO₂ electrolysis (CO₂E) is a promising strategy to reduce greenhouse gas emissions by transforming CO₂ into valuable feedstocks. While recent studies in this field have focused on developing efficient catalyst materials or electrolyzer engineering, the operating temperature's effect has not been systematically examined for zero-gap electrolyzers. To examine the effects of operating temperature, a systematic investigation was conducted using zero-gap (MEA) Cu-based GDEs across a range from room temperature to 80 °C. Our results indicate that increasing the temperature improves CO₂ mass transport, ionic conductivity, and water management, allowing for high catalytic activity toward CO₂E. At operating temperatures greater than 50 °C, selectivity shifted substantially towards CO, with surface enhanced infrared absorption spectroscopy (SEIRAS) showing a concomitant decrease in surface CO coverage at and above this temperature. As commercial electrolyzers will operate at elevated temperatures due to ohmic heating, they may produce a significantly different product distribution than the room-temperature electrolysis prevalent in the literature. Experiments at elevated temperatures demonstrated improved results for CO₂E with industrially relevant current densities (150 mA cm⁻²) over an extended operational period (>200 hours). Additionally, we found that the heating method strongly affects product selectivity and the electrolyzer's performance, emphasizing the need to ensure proper heating while working under these reaction systems.