Direct CO2 Electroreduction from Carbonate

Abstract

The process of CO2 valorization – all the way from capture/concentration of CO2 to its electrochemical upgrade - requires significant inputs in each of the capture, upgrade, and separation steps. The gas-phase CO2 feed following the capture-and-release stage and into the CO2 electroreduction stage produce a large waste of CO2 (between 80 and 95% of CO2 is wasted due to carbonate formation or electrolyte crossover) that adds cost and energy consumption to the CO2 management aspect of the system. Here we report an electrolyzer that instead directly upgrades carbonate electrolyte from CO2 capture solution to syngas, achieving 100% carbon utilization across the system. A bipolar membrane is used to produce proton in situ, under applied potential, which facilitates CO2 releasing at the membrane:catalyst interface from the carbonate solution. Using an Ag catalyst, we generate pure syngas at a 3:1 H2:CO ratio, with no CO2 dilution at the gas outlet, at a current density of 150 mA/cm2, and achieve a full cell energy efficiency of 35%. The direct carbonate cell was stable under a continuous 145 h of catalytic operation at ca. 180 mA/cm2. The work demonstrates that coupling CO2 electrolysis directly with a CO2 capture system can accelerate the path towards viable CO2 conversion technologies.