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.