Potential-Dependent Proton Routing Through Interfacial Water Programming for Acidic CO2 Electroreduction.

Efficient acidic CO2 electroreduction is fundamentally challenged by the dominant hydrogen evolution reaction (HER) and complex proton dynamics across different current densities. Existing catalyst-design strategies primarily optimize static adsorption energetics but rarely address the dynamic evolution of proton transport and interfacial water networks under operating conditions. Herein, we establish a proton-routing interface via integrating axial Cl ligands and in-plane B sites into Ni single-atom catalysts (SACs) to dynamically regulate proton transport and interfacial water structure under operating potentials. At low current densities, axial Cl ligands suppress proton accessibility by disrupting the interfacial hydrogen-bond network, thereby kinetically inhibiting HER. At industrial-current-density conditions, the B sites promote localized water dissociation while simultaneously restricting disordered proton diffusion, enabling targeted proton delivery toward neighboring Ni active centers for efficient proton-coupled CO2 electroreduction. Meanwhile, the synergistic electronic modulation induced by Cl and B optimizes the adsorption energetics of key *COOH and *CO intermediates. Consequently, the optimized Cl─-Ni─NB/CNT catalyst achieves a CO Faradaic efficiency (FEco) of 98.6% at 200 mA cm-2 with remarkable operational stability over 100 h in acidic media. This work introduces a potential-dependent proton-management strategy that transcends traditional electronic-structure-centered catalyst design, providing a generalizable paradigm for steering proton-coupled electrocatalytic pathways.