Sequential vs integrated CO2 capture and electrochemical conversion: An energy comparison

Integrating carbon dioxide (CO2) electrolysis with CO2 capture provides new exciting opportunities for energy reductions by simultaneously removing the energy-demanding regeneration step in CO2 capture and avoiding critical issues faced by CO2 gas-fed electrolysers. However, understanding the potential energy advantages of an integrated capture and conversion process is not straightforward. There are only early-stage demonstrations of CO2 conversion from capture media very recently, and an evaluation of the broader process is paramount before claiming any energy gains from the integration. Here we identify the upper limits of the integrated capture and conversion from an energy perspective by comparing the working principles and performance of integrated and sequential CO2 conversion approaches. Our high-level energy analyses unveil that an integrated electrolysis unit must operate below 1000 kJ/molCO2 to ensure an energy benefit of up to 44% versus the existing state-of-the-art sequential route. However, such energy benefits diminish if future gas-fed electrolysers resolve the carbonation issue and if an integrated electrolyser has poor conversion efficiencies. We conclude with opportunities and limitations to develop industrially relevant integrated electrolysis, providing performance targets for novel integrated electrolysis processes.