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

Electrochemical carbon dioxide reduction reaction (CO 2 RR) under strongly acidic conditions enables high CO 2 utilization. However, especially in proton exchange membrane (PEM) electrode assembly reactors, achieving selective CO 2 RR 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-NH 2 /CNT-SHP) featuring amino (-NH 2 ) functional groups and grafted long-chain hydrophobic molecules. Under acidic conditions, -NH 2 is in situ protonated to form amino cations (-NH 3 ⁺). The positively charged -NH 3 ⁺ groups and hydrophobic molecules effectively disrupt the protonated water (H 3 O + )-rich network, inhibiting the invasion of H 3 O + and thereby suppressing the hydrogen evolution reaction, while enhancing selectivity for acidic CO 2 RR. The catalyst achieves nearly 100% Faradaic efficiency for CO at current densities from 50 to 400 mA cm −2 , with approximately 76% CO 2 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 CO 2 electroreduction.