Bifunctional RhIII-Complex-Catalyzed CO₂ Reduction and NADH Regeneration for Direct Bioelectrochemical Synthesis of C₃ and C₄

This is the authors' abstract. We don't add key points for this paper.

Bioelectrochemical synthesis is emerging as an ecofriendly method for CO 2 fixation, typically using electrochemically regenerated NAD(P)H to supply reducing equivalents for formate dehydrogenase (FDH) to convert CO 2 to formate. However, the efficiency of this process is hindered by unfavorable thermodynamic conditions. In this study, we developed a one-pot bioelectrochemical system featuring a rhodium-based catalyst [Cp*Rh(bpy)Cl] 2+ (Rh III -complex or [Rh III -H 2 O] 2+ ), which works cooperatively with enzymatic cascades involving acetyl-CoA synthase (ACS), acetaldehyde dehydrogenase (ACDH), alcohol dehydrogenase (ADH), formolase (FLS), and d-fructose-6-phosphate aldolase mutant FSA A129S to convert CO 2 into various C 2+ chemicals. The bifunctional Rh III -complex concurrently catalyzes gas-phase reduction of CO 2 to formate at 15.8 mM/h and NADH regeneration at 0.24 mM/min. Formate production is 83.2 times faster than using one of the best aerobic FDHs from Clostridium ljungdahlii ( Cl FDH), resulting in a 3.6-fold increase in methanol production rate (0.43 mM/h) compared to the tandem enzymatic system (0.12 mM/h). Additionally, the bifunctional Rh III -complex cooperates with enzymatic cascades to produce dihydroxyacetone (C 3 ) and L-erythrulose (C 4 ) with yields of 2.63 and 1.93 mM, respectively. This study highlights the synergy between electrochemical and enzymatic catalysis, providing an alternative for electroenzymatic CO 2 reduction to produce value-added C 2+ compounds with enhanced productivity.