Temperature Effects on the Surface CO Population during CO2 Electroreduction over Copper

In industrial implementations, CO₂ electrolyzers will likely operate at high temperatures due to heat transfer limitations, but the effects of temperature on surface reactions involved in CO₂ electroreduction remain elusive and heavily based on inference from product analysis. In this study, we used surface-enhanced infrared absorption spectroscopy (SEIRAS) to deconvolute temperature-dependent phenomena affecting the CO population on copper between 20 and 80 °C. We show that CO coverage and migration to defect sites increase between 20 and 45 °C and decrease between 45 and 80 °C, suggesting that increasing temperature favors a CO hydrogenation route to C₁ products over a CO coupling route to C₂₊ products. C₁ and C₂₊ product formation rates have 1.28 and 1.95 order dependence on the concentration of CO on defect sites, respectively, indicating that these are the active sites for product formation between 20 and 80 °C. Thus, increasing temperature has a direct effect on the CO conversion route to C₁ and C₂₊ products beyond just controlling local CO₂ availability, mass transport, and elementary reaction rates. These findings provide a deeper understanding of the underlying reaction mechanism at elevated temperatures, which is a key step in rationalizing product distribution and in designing solutions for enhanced C₂₊ production in CO₂ electrolyzers.