Computational electrocatalysis beyond conventional hydrogen electrode model: CO reduction to C species on copper facilitated by dynamically formed solvent halide ions at the solid-liquid interface.

The reduction of CO into value-added chemicals and fuels has been actively studied as a promising strategy for mitigating carbon dioxide emissions. However, the dilemma for the experimentalist in choosing an appropriate reaction medium and neglecting the effect of solvent ions when using a simple thermochemical model, normally leads to the disagreement between experimental observations and theoretical calculations. In this work, by considering the effects of both the anion and cation, a more realistic CO reduction environment at the solid-liquid interface between copper and solvent ions has been systematically studied by using molecular dynamics and density functional theory. We revealed that the co-occurrence of alkali ions (K) and halide ions (F, Cl, Br, and I) in the electric double layer (EDL) can enhance the adsorption of CO by more than 0.45 eV compared to that in pure water, and the calculated energy barrier for CO-CO coupling also decreases 0.32 eV in the presence of I ion on a negatively charged copper electrode. The hydrated ions can modulate the distribution of the charge near the solid-liquid interface, which significantly promotes CO reduction and meanwhile impedes the hydrogen evolution reaction. Therefore, our work unveils the significant role of halide ions at the electrode-electrolyte interface for promoting CO reduction on copper electrode.