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

Abstract

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.