Understanding the Temperature Effect on Carbon‐Carbon Coupling during CO2 and CO Electroreduction in Zero‐Gap Electrolyzers†

Comprehensive Summary Cu‐catalyzed electrochemical CO 2 reduction reaction (CO 2 RR) and CO reduction reaction (CORR) are of great interest due to their potential to produce carbon‐neutral and value‐added multicarbon (C 2+ ) chemicals. In practice, CO 2 RR and CORR are typically operated at industrially relevant current densities, making the process exothermal. Although the increased operation temperature is known to affect the performance of CO 2 RR and CORR, the relationship between temperatures and kinetic parameters was not clearly elaborated, particularly in zero‐gap reactors. In this study, we detail the effect of the temperature on Cu‐catalyzed CO 2 RR and CORR. Our electrochemical and operando spectroscopic studies show that high temperatures increase the activity of CO 2 RR to CO and CORR to C 2 H 4 by enhancing the mass transfer of CO 2 and CO. As the rates of these two processes are highly influenced by reactant diffusion, elevating the operating temperature results in high local CO 2 and CO availability to accelerate product formation. Consequently, the *CO coverage in both cases increases at higher temperatures. However, under CO 2 RR conditions, *CO desorption is more favorable than carbon‐carbon (C—C) coupling thermodynamically at high temperatures, causing the reduction in the Faradaic efficiency (FE) of C 2 H 4 . In CORR, the high‐temperature‐augmented CO diffusion overcomes the unfavorable adsorption thermodynamics, increasing the probability of C—C coupling.