Electrochemical Conversion of CO 2 at Pressures Ranging from 1 to 75 Bar Using Porous Copper Electrodes in a 0.1 M Potassium Bicarbonate

Electrochemical conversion of CO 2 is essential, producing valuable products while maintaining a closed carbon cycle. Previously, CO 2 solubility data were measured over a pressure range of 1–50 bar using 0.1 M NaHCO 3 at 313 K, achieving maximum Faradaic efficiencies (FE) of 75% for CO 2 reduction with an In electrode at 40 bar and 298 K. However, no prior study has concurrently correlated CO 2 electroreduction behavior with CO 2 solubility in a 0.1 M potassium bicarbonate (KHCO 3 ) electrolyte measured at higher pressures, up to 75 bar, and 313 K. Electrochemical analyses, including cyclic voltammetry and chronoamperometry, were performed using a porous copper electrode at 40°C and CO 2 pressures of 1, 20, and 45 bar (gaseous state) and 75 bar (supercritical state). A single-compartment chamber without a membrane was employed when both applied potential and pressure were varied. In a 0.1 M KHCO 3 electrolyte, increasing CO 2 pressure enhanced the formation of both CH 4 and HCOOH. Under supercritical CO 2 condition at 75 bar, maximum FE of 30.6% for CH 4 and 40.4% for HCOOH were obtained. This improvement is attributed to higher CO 2 solubility and pH reduction at elevated pressures. An exponential increase in FE was observed with increasing CO 2 solubility. The higher cell potential (−1.2 V) increased the Faradaic efficiency significantly.