Bifunctional Rh<sup>III</sup>-Complex-Catalyzed CO<sub>2</sub> Reduction and NADH Regeneration for Direct Bioelectrochemical\nSynthesis of C<sub>3</sub> and C<sub>4</sub>

Bioelectrochemical\nsynthesis is emerging as an ecofriendly method\nfor CO<sub>2</sub> fixation, typically using electrochemically regenerated\nNAD(P)H to supply reducing equivalents for formate dehydrogenase (FDH)\nto convert CO<sub>2</sub> to formate. However, the efficiency of this\nprocess is hindered by unfavorable thermodynamic conditions. In this\nstudy, we developed a one-pot bioelectrochemical system featuring\na rhodium-based catalyst [Cp*Rh(bpy)Cl]<sup>2+</sup> (Rh<sup>III</sup>-complex or [Rh<sup>III</sup>-H<sub>2</sub>O]<sup>2+</sup>), which\nworks cooperatively with enzymatic cascades involving acetyl-CoA synthase\n(ACS), acetaldehyde dehydrogenase (ACDH), alcohol dehydrogenase (ADH),\nformolase (FLS), and d-fructose-6-phosphate aldolase mutant FSA<sup>A129S</sup> to convert CO<sub>2</sub> into various C<sub>2+</sub> chemicals. The bifunctional Rh<sup>III</sup>-complex concurrently\ncatalyzes gas-phase reduction of CO<sub>2</sub> to formate at 15.8\nmM/h and NADH regeneration at 0.24 mM/min. Formate production is\n83.2 times faster than using one of the best aerobic FDHs from Clostridium ljungdahlii (<i>Cl</i>FDH),\nresulting in a 3.6-fold increase in methanol production rate (0.43\nmM/h) compared to the tandem enzymatic system (0.12 mM/h). Additionally,\nthe bifunctional Rh<sup>III</sup>-complex cooperates with enzymatic\ncascades to produce dihydroxyacetone (C<sub>3</sub>) and L-erythrulose\n(C<sub>4</sub>) with yields of 2.63 and 1.93 mM, respectively. This\nstudy highlights the synergy between electrochemical and enzymatic\ncatalysis, providing an alternative for electroenzymatic CO<sub>2</sub> reduction to produce value-added C<sub>2+</sub> compounds with enhanced\nproductivity.