Electrochemical CO2 reduction on a copper foam electrode at elevated pressures

Electrochemical CO2 reduction is a promising way of closing the carbon cycle while synthesizing useful commodity chemicals and fuels. One of the possible routes to scale up the process is CO2 reduction at elevated pressure, as this is a way to increase the concentration of poorly soluble CO2 in aqueous systems. Yet, not many studies focus on this route, owing to the inherent challenges with high-pressure systems, such as leaks, product quantification, and ease of operation. In this study, we use a high-pressure flow cell setup to investigate the impact of CO2 pressure on the electrochemical performance of a copper foam electrode for CO2 reduction within a pressure range of 1 to 25 bar. Our initial findings using a 0.5 M potassium bicarbonate (KHCO3) electrolyte show a consistent improvement in selectivity towards CO2 reduction products, with HCOOH being the dominant product. By conducting a systematic exploration of operating parameters including applied current density, applied CO2 pressure, cation effect, and electrolyte concentration, the selectivity towards formate (HCOOH) is optimized, achieving a remarkable 70 % faradaic efficiency (FE) under moderate conditions of 25 bar in a 0.5 M cesium bicarbonate (CsHCO3) electrolyte. Additionally, we report the synthesis of isopropanol with a FE of 11 % at the 25 bar in 0.5 M KHCO3 which is the highest reported selectivity towards isopropanol on copper using a bicarbonate system.