Bioelectrocatalytic CO₂ Reduction by Mo-Dependent Formylmethanofuran Dehydrogenase

Massive efforts are invested in developing innovative CO₂ -sequestration strategies to counter climate change and transform CO₂ into higher-value products. CO₂ -capture by reduction is a chemical challenge, and attention is turned toward biological systems that selectively and efficiently catalyse this reaction under mild conditions and in aqueous solvents. While a few reports have evaluated the effectiveness of isolated bacterial formate dehydrogenases as catalysts for the reversible electrochemical reduction of CO₂ , it is imperative to explore other enzymes among the natural reservoir of potential models that might exhibit higher turnover rates or preferential directionality for the reductive reaction. Here, we present electroenzymatic catalysis of formylmethanofuran dehydrogenase, a CO₂ -reducing-and-fixing biomachinery isolated from a thermophilic methanogen, which was deposited on a graphite rod electrode to enable direct electron transfer for electroenzymatic CO₂ reduction. The gas is reduced with a high Faradaic efficiency (109±1 %), where a low affinity for formate prevents its electrochemical reoxidation and favours formate accumulation. These properties make the enzyme an excellent tool for electroenzymatic CO₂ -fixation and inspiration for protein engineering that would be beneficial for biotechnological purposes to convert the greenhouse gas into stable formate that can subsequently be safely stored, transported, and used for power generation without energy loss.