Go with CO: A Case for Targeting Carbon Monoxide As a Reactive Carbon Capture Product

This study is relevant to reactive carbon capture using aqueous alkaline capture solutions, where captured CO2 is electrochemically released from a capture solution and then upgraded into commodity chemicals in an electrolyzer. The commercial viability of this form of reactive carbon capture demands that the electrolyzer effluent that is returned to the capture unit be sufficiently alkaline to effectively capture CO2 from air or a point source. Here, we introduce “electron-alkalinity efficiency” (EA%) to correlate OH– production to electrons consumed during the electrolysis of CO2. We show that the maximum EA% value for CO production is 100%, but is less than 50% for the production of HCOO–, CH4, and C2H4. This outcome implies that the electrolytic production of CO yields the highest CO2 capture efficiency. To support this claim, we modeled a 1-m2 electrolyzer producing CO at a current density of 200 mA cm–2, 100% Faradaic efficiency for CO, and 100% CO2 utilization, resulting in an OH– production rate of 75 mol h–1. No other CO2 reduction products (HCOO–, CH4, and C2H4) generate this level of alkalinity without operating at far more extreme current densities or larger scales. We therefore recommend to “go with CO” for reactive carbon capture.