Engineering Hydrogen‐Down Water Configurations for Ampere‐Level Electrochemical CO ₂ Reduction to Formate

ABSTRACT Electrochemical CO 2 reduction (ECR) to formate offers a sustainable chemical production pathway, but industrial‐scale performance is hindered by limited proton availability at high current densities. While previous research has focused on catalyst electronic structure and CO 2 activation, the role of interfacial water configurations in controlling water dissociation kinetics has been overlooked. We manipulate interfacial water molecular orientations using HfO 2 as a molecular switch on Bi surfaces, favoring hydrogen‐down (OH 2 ↓) over oxygen‐down (H 2 O↓) configurations. The OH 2 ↓ orientation significantly reduces water dissociation energy barriers, producing active hydrogen species, as confirmed by ab initio molecular dynamics simulations and density functional theory calculations. Multiple in situ characterizations validate interfacial water structural changes. HfO 2 ‐modified Bi achieves exceptional formate partial current density (−970 mA cm −2 ) with 97% faradaic efficiency. In the membrane electrode assembly, the catalyst demonstrates high formate selectivity (>90%) across 0.2–1.6 A, establishing interfacial water engineering as a promising strategy for industrial‐scale ECR catalysts.