(664b) Correlating CO Coverage and CO Electroreduction on Cu Via High-Pressure in Situ Spectroscopic and Reactivity Investigations

The understanding of CO₂ reduction reaction (CO₂RR) mechanisms on Cu surfaces is essential for enhancing the conversion of CO₂ into value-added multicarbon (C₂₊) products. The electroreduction of CO, the undisputed intermediate in the formation of methane and C₂₊ products, serves as an ideal proxy for mechanistic study because it removes the complexity of multiple aqueous phase equilibria among CO₂, HCO₃^- and CO₃^2-, while the absolute coverage of CO has been a missing piece in mechanistic puzzle of CO reduction reaction (CORR) on Cu. In this talk, we present a high-pressure in situ surface enhanced infrared spectroscopy method at CO pressures up to 60 barg to reveal the upper bound of the CO coverage under electrocatalytic conditions to be 0.05 monolayer at atmospheric CO pressure and the saturation CO coverage to be ~0.25 monolayer based on the dynamical dipole coupling behavior of adsorbed CO. Combining with reactivity investigation at corresponding pressures, we present several new insights into the CO₂RR mechanism. (1) C-C coupling is unlikely the rate-determining step for C₂₊ product formation, as reaction orders with respect to adsorbed CO are significantly less than unity; (2) increased CO coverage enhances selectivity towards oxygenates, particularly acetate, due to reduced C affinity; (3) high CO coverage likely promotes a novel symmetrical C-C coupling mechanism, yielding uncommon products such as ethane, glycolaldehyde, and ethylene glycol. This study provides an effective approach to bridge the coverage of reactant adsorbate and reactivity to reveal the mechanism of electrochemical reaction involving gaseous molecules, which is essentially beneficial for the design of advanced catalysts and reaction system.