Bifunctional Artificial Carbonic Anhydrase for the Integrated Capture and Electrochemical Conversion of CO2

To valorize waste and atmospheric CO2, carbon capture and utilization (CCU) technologies are currently receiving a lot of attention. Alkali base solutions have shown to be efficient capture solutions, and the electrochemical CO2 reduction (eCO2R) is a promising approach to convert CO2 using renewable energy. However, the capture and conversion have been investigated almost exclusively as separate processes to date. This strategy has the disadvantage that CO2 must be desorbed and compressed after capture, which increases the capital and operational costs of the technology significantly. To improve the valorization potential of CCU technologies, integrating both the capture and electrochemical conversion steps by directly utilizing the postcapture solution as an electrolyte (in the form of bicarbonate) for the eCO2R is a highly promising approach. However, bicarbonate electrolysis cannot compete yet in terms of energy efficiency with analogous CO2-fed electrolyzers. Nevertheless, given its huge potential, there is interest in optimizing the overall technology by, for instance, decreasing the costs of capturing the CO2 by shortening the operational time or promoting the electrochemical conversion of CO2 in bicarbonate solutions. In this study, we have synthesized and optimized for the first time ever bioinspired catalysts that were able to fulfill and improve steps in a combined CO2 capture and conversion system. In the best-case scenario, the rate of the conversion of CO2 to bicarbonate (mimicking the capture step in CCU) increased by 91% when the biomimetic catalyst [Zn(cyclen)]2+ was present in the capture solution. On the other hand, the same catalyst promoted the electrochemical conversion of CO2 to formate from a bicarbonate postcapture solution by inhibiting the competing hydrogen evolution reaction (HER). The partial current density toward the HER decreased from 18 mA cm–2 in control experiments to 0.7 mA cm–2 in the presence of [Zn(cyclen)]2+.