Direct carbonate electrolysis into pure syngas

Abstract

Syngas, a mixture of carbon monoxide (CO) and hydrogen (H2), is a feedstock for a wide variety of chemical processes and is currently produced from fossil fuels. The need to reduce carbon dioxide (CO2) emissions motivates the production of syngas from atmospheric CO2, powered by renewable electricity. Current CO2 electrolyzers require costly separation processes to purify the CO2 reactant stream and to remove unreacted CO2 from the product stream. We demonstrate direct carbonate electrolysis (DCE) in a reactive capture system that avoids the initial CO2 purification process and produces pure syngas with sufficient CO content for direct industrial use (H2/CO ratios of 1–2). The DCE system incorporates a composite CO2 diffusion layer (CDL) that attains high CO selectivity by achieving high alkalinity and available CO2 concentration at the cathode. Applying this strategy, we produce pure syngas in the cathode outlet gas stream with a H2/CO ratio of 1.16 at 200 mA cm-2, corresponding to a CO faradaic efficiency (FE) of 46% and an energy intensity of 52 GJ tsyngas-1. By eliminating intensive upstream and downstream processes, DCE achieves syngas production with 13% less energy than CO2 electrolysis combined with water electrolysis, 39% less energy than past carbonate reduction work, and 75% fewer emissions than the conventional fossil fuel based route.