Surface-Hydrogen Modulated Hydrogen Bond Network Steering Two-Electron Pathways in CO ₂ Electroreduction on Cu Surface

In computational electrochemistry, the adsorption strength of key intermediates is widely considered to be the primary factor determining product selectivity. However, in CO2 electroreduction, the *OCHO* intermediate leading to HCOOH adsorbs more strongly than *COOH leading to CO on most d-block metals, including CO-selective ones. This discrepancy has been attributed to the instability of the *OCO* precursor kinetically hindering *OCHO* formation. Interestingly, Cu exhibits comparable selectivity for both HCOOH and CO, prompting investigation of the underlying mechanisms. Herein, using ab initio molecular dynamics simulations combined with explicit solvation and kinetic simulations, we reveal that the modulated hydrogen bond network induced by surface hydrogen (*H) plays a critical role in controlling the reaction pathways on Cu. This reorganized network induces a correlated motion between CO2 and *H, which facilitates the formation of *OCHO*, resulting in similar activation barriers and partially overlapping pathways for CO and HCOOH. These findings offer a unified mechanism for understanding the divergence and connection of the two-electron pathways on Cu, and highlight the importance of interfacial structure in electrocatalysis and future catalyst design.