Energy-Efficient Electrified Reactive Capture to Syngas Via Tuning of Morphology and Energetics of Catalyst Supports

Direct-air capture (DAC) of CO2 often uses alkali hydroxides as sorbent, and relies on an energy-intensive thermal CaCO3/Ca(OH)2 step to release CO2 and regenerate the alkali hydroxide. Reactive capture instead converts the captured CO2 to value-add products while regenerating the capture liquid. Here we investigate the limitations of performance in prior electrochemical reactive capture systems, finding that the catalyst becomes starved of CO2 even at moderate current densities, this leading to a rapid decline in faradaic efficiency. We explored catalysts employing both microposity and micromesoporosity, finding that in the case of the best-designed supports, efficient mass transport of the carbonate feedstock is maintained up to 200 mA/cm2 current densities. Because the CO2-to-CO catalyst, metal-phthalocyanine, tends to aggregate under bias, degrading CO2 reduction activity, we then immobilized the CoPc on a polydopamine support, producing an even dispersion of catalyst on the support surface; the polydopamine further produces a desired electron-deficient Co center in the heterogenized CoPc. We report carbonate electrolysis at 200 mA cm–2 at 3.0 V with faradaic efficiency of 43% for CO with < 1% CO2 in the outlet stream. A carbonate-to-syngas system using this reaction-capture approach has a projected energy efficiency of 50% at 200 mA cm–2 when H2 is provided to form 2:1 H2:CO syngas by coupling with a water electrolyzer. Durability studies show 40 h of initial operating stability.