Continuous production of pure liquid fuel solutions via electrocatalytic CO2 reduction using solid-electrolyte devices

Abstract

Electrocatalytic CO2 reduction is often carried out in a solution electrolyte such as KHCO3 (aq) for ion conduction. Therefore, liquid products that form are in a mixture with the dissolved salts, requiring energy-intensive downstream separation. Here we report continuous electrocatalytic conversion of CO2 to pure liquid fuel solutions in cells that utilise solid electrolytes, where electrochemically generated cations (such as H+) and anions (such as HCOO-) are combined to form pure product solutions without mixing with other ions. Using a HCOOH-selective (Faradaic efficiencies > 90%) and easily-scaled Bi catalyst at the cathode, we demonstrate production of pure HCOOH solutions with concentrations up to 12 M. We also show 100-hour continuous and stable generation of 0.1 M HCOOH with negligible degradation in selectivity and activity. Production of other electrolyte-free C2+ liquid oxygenate solutions, including acetic acid, ethanol, and n-propanol, are also demonstrated using a Cu catalyst. Finally, we show that our CO2 reduction cell with solid electrolytes can be modified to suit other, more complex practical applications.