Effect of CO2 deficiency on the performance of membrane electrode CO2 electrolyzer

To mitigate greenhouse effects, carbon dioxide reduction reaction (CO₂RR) has been used as an efficient means of carbon reduction. In CO₂ electrolyzer, CO₂ deficiency can happen and degrade the reaction efficiency. Herein, an efficient and long-lived formic acid three-cell electrolyzer is used to study the effect of CO₂ deficiency, by operating the electrolyzer from full CO₂ supply to CO₂ deficiency. In addition, the effects of various CO₂ fluxes and concentrations on the electrolyzer current, acid concentration and lifetime are investigated. This study quantitatively reveals the impact of CO₂ deficiency on current density, product selectivity, and electrolyzer lifetime. The findings indicate that current density decreases by 12.74 %, while CO₂ conversion efficiency drops by 92.5 %, demonstrating a significant reduction in the reactivity of CO₂ conversion to formate ions. Conversely, the hydrogen evolution reaction is enhanced. Prolonged CO₂ deficiency (below 13 ml/min) can also lead to catalyst degradation, including separation and dissolution within the cathode catalyst layer, ultimately diminishing overall performance. Compared with the CO₂ flux, the CO₂ concentration exerts a more pronounced influence. To ensure the electrolysis efficiency, the carbon dioxide concentration should not be less than 80 %.