Electrochemical capture and conversion of CO2 into syngas

Abstract

For waste CO2 to be electrolytically converted into higher-value chemicals and fuels, electrolyzers that drive the CO2 reduction reaction need to be integrated with upstream CO2 capture units. However, this has not yet been demonstrated because of the large operational gap for the capture and conversion steps. Here, we report a coupled carbon reactor that captures and converts CO2 into syngas with a 1.7:1 ratio of H2 to CO. The resulting syngas can be utilized in the production of a wide range of valuable chemicals. This CCR uses a packed bed absorption column (“capture unit”) to react alkaline aqueous solution enriched in K2CO3(aq) with CO2 to form bicarbonate enriched solutions (“reactive carbon solutions”). These reactive carbon solutions are then fed into an electrochemical reactor (“bicarbonate electrolyzer”) to form CO(g) and OH– product. This alkaline product is then passed through a gas-liquid separator (“separator”) and recycled back to the capture unit for further reaction with CO2(g). These collective elements close the full loop for CO2 capture and conversion. An electrochemically inert CO2 capture promoter (glycine) was used to better match the CO2 capture rates in the absorption column to the OH– production rates in the electrolyzer, thereby producing CO at steady-state without intervention. We demonstrate that the CCR captures and converts CO2 from simulated flue gas (20% CO2; 80% N2) into CO with a Faradaic efficiency of 30% at 100 mA cm–2 for 30 hours of operation.