Interface engineering of single-molecular heterojunction catalysts for CO₂ electroreduction in strong acid medium

Electrochemical carbon dioxide reduction reaction (CO₂RR) under strongly acidic conditions enables high CO₂ utilization. However, especially in proton exchange membrane (PEM) electrode assembly reactors, achieving selective CO₂RR in such environments remains challenging due to uncontrolled interfacial water diffusion at high current densities. Here, we develop a nickel-based heterogeneous molecular electrocatalyst (NiPc-NH₂/CNT-SHP) featuring amino (-NH₂) functional groups and grafted long-chain hydrophobic molecules. Under acidic conditions, -NH₂ is in situ protonated to form amino cations (-NH₃⁺). The positively charged -NH₃⁺ groups and hydrophobic molecules effectively disrupt the protonated water (H₃O⁺)-rich network, inhibiting the invasion of H₃O⁺ and thereby suppressing the hydrogen evolution reaction, while enhancing selectivity for acidic CO₂RR. The catalyst achieves nearly 100% Faradaic efficiency for CO at current densities from 50 to 400 mA cm^-2, with approximately 76% CO₂ utilization efficiency in a flow cell, and sustains over 80% selectivity for more than 200 h in a self-designed PEM-porous solid electrolyte reactor. These findings highlight interfacial water management as a key design principle for efficient acidic CO₂ electroreduction.