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.