Enzymatic Flow Electrolyzer for CO ₂ and Waste Comproportionation to Formate and Its Use in Photocatalytic Alkene Hydrocarboxylation

Paired electrolysis enables the simultaneous coupling of CO₂ reduction with anodic waste upcycling to form valuable products. However, achieving selective, efficient, and stable product formation and coupling to downstream valorization remains a challenge. In this study, W-containing formate dehydrogenase from Nitratidesulfovibrio vulgaris Hildenborough is immobilized onto a cathode made from carbon felt coated with porous TiO₂ and paired with a commercial Ni foam anode to assemble a semiartificial flow electrolyzer for the simultaneous conversion of CO₂ and waste (plastic and biomass) to the single product formate. The enzymatic flow electrolyzer achieved an initial cell faradaic efficiency toward formate of almost 200%, a maximum CO₂ conversion yield of 18% and can operate at a low full-cell voltage of -1.5 V for 122 h, which allows for bias-free operation with a silicon photovoltaic cell. The aqueous formate produced in the enzymatic electrolyzer was subsequently utilized downstream as a C₁ building block in the photocatalytic hydrocarboxylation of alkenes, providing a path for the domino valorization of CO₂ and waste toward bulk and fine chemical synthesis.