High-Pressure Electrochemical CO ₂ Capture and Reduction to Formic Acid

Direct supply of dilute CO2 sources to an electrochemical porous solid electrolyte (PSE) reactor enables simultaneous CO2 capture and conversion. However, its catalytic performance is significantly limited under ambient pressure due to low CO2 surface coverage and mass transport constraints. Here, we demonstrate a high-pressure CO2 reduction reaction (CO2RR) of a dilute stream in a PSE reactor, achieving markedly enhanced formic acid selectivity. Pressurizing a 5 mol % CO2 gas stream to 10 atm led to a Faradaic efficiency for formic acid (FEHCOOH) of up to 81.0% at 100 mA cm–2, compared to only 47.8% under ambient conditions. By balancing the liquid pressure within the PSE layer with the cathode gas pressure, we minimized the transmembrane pressure differential, enabling stable operation for 90 h at 20 atm. In addition, high-pressure operation shifted the cathode-membrane interfacial pH from a carbonate-dominated regime toward bicarbonate, thereby improving the electron efficiency of the simultaneous carbon capture process by up to 57.0% during the conversion process.