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 (FE_co) 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.