(623a) Temperature Effects on the Surface Dynamics of the CO2 Reduction Reaction over Copper

The electrochemical reduction of CO₂ (CO₂RR) has stood out as a pathway to mitigate carbon emissions and supply multi-carbon feedstocks to the chemical industry. While most CO₂RR studies over copper are carried out at room temperature, heat transfer limitations in the electrolyte will result in temperature buildup near the electrode in industrial CO₂ electrolyzers. Reaction temperature plays a key role in the reaction activity and product selectivity by controlling the distribution of species on the copper surface. In this study, we use surface enhanced infrared absorption spectroscopy (SEIRAS) and surface enhanced Raman spectroscopy (SERS) to investigate the effect of temperature on the dynamics of reactive intermediates in the reaction microenvironment (Fig. A).

Using SEIRAS, we showed site-specific CO coverage is dependent on temperature, and how CO migration seems to directly impact product distribution at higher temperatures. We found that increasing temperature leads to decreased CO and increased alkyl groups coverage for a given potential (Fig. B). This suggests that temperature has a direct effect on the selection of mechanistic pathways in the conversion of CO to C₁ and C₂ products, beyond just controlling mass transport and local CO₂ availability. Using SERS, we showed that the local pH is considerably higher than their bulk values, and that higher temperatures consistently led to higher local pH values (Fig. C). The significant depletion of local hydrogen with increasing temperature indicates that local pH plays a key role in driving reaction selectivity dependence on temperature. Understanding the effect of temperature on the CO₂RR surface dynamics through surface sensitive techniques is a key step to rationalize product distribution and to design solutions for enhanced C₂₊ production in industrial CO₂ electrolyzers.