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

Direct supply of dilute CO 2 sources to an electrochemical porous solid electrolyte (PSE) reactor enables simultaneous CO 2 capture and conversion. However, its catalytic performance is significantly limited under ambient pressure due to low CO 2 surface coverage and mass transport constraints. Here, we demonstrate a high-pressure CO 2 reduction reaction (CO 2 RR) of a dilute stream in a PSE reactor, achieving markedly enhanced formic acid selectivity. Pressurizing a 5 mol % CO 2 gas stream to 10 atm led to a Faradaic efficiency for formic acid (FE HCOOH ) 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.