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 CO 2 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 CO 2 from air or a point source. Here, we introduce “electron-alkalinity efficiency” (EA%) to correlate OH – production to electrons consumed during the electrolysis of CO 2 . We show that the maximum EA% value for CO production is 100%, but is less than 50% for the production of HCOO –, CH 4, and C 2 H 4 . This outcome implies that the electrolytic production of CO yields the highest CO 2 capture efficiency. To support this claim, we modeled a 1-m 2 electrolyzer producing CO at a current density of 200 mA cm –2, 100% Faradaic efficiency for CO, and 100% CO 2 utilization, resulting in an OH – production rate of 75 mol h –1 . No other CO 2 reduction products (HCOO –, CH 4, and C 2 H 4 ) 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.