Ammonia-Mediated CO2 Capture and Direct Electroreduction to Formate

Abstract

Direct electrochemical conversion of CO2 capture solutions (instead of gaseous CO2) to valuable chemicals can circumvent the energy-intensive CO2 regeneration and pressurization steps, but the performance of such processes is limited by the sluggish release of CO2 and the use of energy-consuming bipolar membranes (BPMs). Herein, we discovered that an ammonium bicarbonate (NH4HCO3)-fed electrolyzer outperforms the state-of-the-art KHCO3 electrolyzers largely because of its favorable thermal decomposition property, which allows for a 3-fold increase in the in situ CO2 concentration, a maximum 23% increase in formate faradaic efficiency, and a 35% reduction in cell voltage by substituting BPM with an anion exchange membrane (AEM). We then demonstrated an integrated process by combining NH4HCO3 electrolysis with CO2 capture by on-site generated ammonia from the electroreduction of nitrate, which features a remarkable 99.8% utilization of of CO2 capturing agent. Such a multipurpose process offers a sustainable route for the simultaneous removal of N wastes and streamlined CO2 capturing and upgrading.