Dynamic Proton Gating via Interfacial Water Programming Enables Near-Unity CO ₂ -to-CO Conversion in Acid

The efficient electroreduction of CO2 in acidic electrolytes is severely limited by the dominant hydrogen evolution reaction (HER). This challenge is exacerbated at hydrophobic interfaces, where proton dynamics become complex and difficult to control. Here, we report a “dynamic interfacial gating” strategy that actively steers proton-transfer pathways by reprogramming the water network on a superhydrophobic catalyst. Using an axial chloride ligand anchored on a Ni−N4 site (UHD−NiN4Cl−C) as a gate, we selectively stabilize a structured, nanoconfined water cluster. Unlike the chloride-free analog (UHD−NiN4−C), where the applied potential disrupts the hydrogen-bond network and triggers rampant proton migration for the HER, this ligand-templated cluster facilitates targeted water dissociation, supplying protons specifically for the CO2 reduction reaction while preserving global hydrophobicity. Consequently, the UHD−NiN4Cl−C catalyst achieves >99.4% Faradaic efficiency for CO production across an exceptionally broad potential window (−0.8 to −2.0 V vs. RHE), with a lower Tafel slope than UHD−NiN4−C. This work transcends traditional electronic structure modulation, establishing a dynamic, ligand-mediated approach to control the interfacial microenvironment for precise proton-coupled electron transfer.