Decoupling Charge Carrier Electroreduction and Enzymatic\nCO<sub>2</sub> Conversion to Formate Using a Dual-Cell Flow Reactor\nSystem

With an efficient\natom economy, low activation energy, and valuable\napplications for fuel cells and hydrogen storage, formic acid (FA)\nis a useful fuel product to convert CO<sub>2</sub> and reduce emissions.\nAlthough metal catalysts are typically used for this conversion, unwanted\nside reactions remain a concern, particularly when products are attempted\nto be recovered long-term. In this study, an enzymatic catalyst is\nused to enable the selective conversion of CO<sub>2</sub> to FA, as\na formate ion. A dual-cell flow reactor system is used to first reduce\na charge mediator electrochemically (reduction cell), which then activates\na catalyst to selectively convert CO<sub>2</sub> to formate (production\ncell). This approach minimizes enzyme degradation by avoiding direct\ncontact with increased voltages and improves the quantity of formate\nproduced. The system produced 25 mM of formate and reached over 50%\nCoulombic efficiency. The larger volume of this dual-cell system increases\nthe quantity of formate produced beyond that of a batch cell. Additional\ndesign configurations are employed, including a pH control pump to\nmaintain catalyst activity and a packed bed reactor to improve contact\nof the charge carrier with the catalyst. Both configurations retained\nhigher production and efficiency long-term (∼168 h). The results\nhighlight the challenges of developing a system where many parameters\nplay a role in optimizing performance. Nevertheless, the ability of\nthe system to produce formate from CO<sub>2</sub> demonstrates the\npotential to improve upon this configuration for a variety of electrochemical\nCO<sub>2</sub> conversion applications.