Temperature-Dependent Adsorbate-Induced Surface Roughening Onset in Electrochemical CO ₂ Reduction on Copper

The dynamic restructuring of Cu surfaces under electrochemical CO₂ reduction conditions is crucial for determining their catalytic performance, particularly for multicarbon products such as ethylene and propanol. Temperature strongly influences this restructuring, yet its effect on surface states and CO₂RR selectivity remains unclear. Here, we explore the chemical space of Cu under CO and H coverage at different temperatures, including the change in adsorbate-induced surface roughening, by combining grand canonical DFT with global optimization methods to construct a potential-dependent grand canonical ensemble. By tuning the temperature, we modulate adsorbate chemical potentials, which alters the accessible surface states. Quasi-kinetic Monte Carlo simulations track the system's evolution during a simulated cathodic scan, revealing metastable structures at the CO₂RR onset potential (-1.1 V vs RHE). Our results show that increasing temperature tends to decrease the roughening of the Cu surface due to a sharpened phase transition between CO-only and H-only coverages. Critically, this leads to diminished coexistence of CO and H on the surface─previously found to be required for the onset of surface reconstruction. Meanwhile, CO coverage decreases overall, explaining the experimentally observed decline in C₂ product selectivity and enhanced hydrogen evolution. This work provides atomistic insights into temperature-dependent surface state evolution and CO₂RR performance.