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

Abstract

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.

Advancing integrated CO2 electrochemical conversion with amine-based CO2 capture: a review

“…33,37,45,60,62,69,70 However, the performance of the integrated electrolyser is usually inferior to the state-of-the-art gas-fed electrolyser in terms of product Faradaic efficiency, current densities, and cell potentials. performance of these two electrolysers to convert CO 2 to CO. 36 More importantly, recent studies demonstrate the potential to improve the Faradaic efficiency and current densities for direct CO 2 conversion in an amine-based capture medium by tailoring the electrode structures, local reaction environment, and operating conditions such as temperatures and pressures, and cell design. A summary of achievements in recent studies is listed in Table 1.…”

“…6b from our recent energy analyses for CO 2 -to-CO highlight the importance of product faradaic efficiency and cell potentials for the overall energy efficiency, where product faradaic efficiency serves a more critical role than cell potential. 36 Therefore, this section will review recent advances in improving the faradaic efficiency and current densities via electrode innovation and modification of the local reaction environment.…”

“…Most of the reported activity and product selectivity for CO 2 electroreduction in the amine-based capture medium is also inferior to the performance of gas-fed CO 2 conversion. As a result, the overall energy efficiency of the integrated electrolyser is much lower than the gas-fed electrolyser 36 and makes the overall process intensification less economically attractive than the sequential route. This review aims to provide an overview of the most recent advances in improving CO 2 electroreduction, mainly in amine-based capture media, focusing on the unique features of CO 2 electroreduction in the capture media compared to the gas-fed electroreduction.…”

“…Our recent energy analyses 36 over sequential and coupled routes revealed that about 42% of overall energy could be saved for the integrated route if the integrated electrolyser can be operated at the same energy efficiency (∼1000 kJ mol CO 2 converted −1 ) as the state-of-the-art gas-fed electrolyser (3 V and 90% CO faradaic efficiency). The development of the integrated electrolyser is the crucial step enabling a more efficient coupled process and further cost reduction for the CO 2 capture and utilisation.…”

“…Most of the reported activity and product selectivity for CO 2 electroreduction in the amine-based capture medium is also inferior to the performance of gas-fed CO 2 conversion. As a result, the overall energy efficiency of the integrated electrolyser is much lower than the gas-fed electrolyser 36 and makes the overall process intensification less economically attractive than the sequential route.…”