Ammonia-Mediated CO<sub>2</sub> Capture and Direct Electroreduction to Formate
Hengzhou Liu, Yifu Chen, Jungkuk Lee, Shuang Gu, Wenzhen Li
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.