Enzymatic Flow Electrolyzer for CO₂ 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 demonstrate the first enzymatic 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 towards formate of almost 200%, a maximum CO2 conversion yield of 18% and can operate at a very low full-cell voltage of −1.5 V for 122 h, which enables the bias-free operation with a silicon photovoltaic cell. The aqueous formate produced in the semiartificial electrolyzer was further utilized downstream as a C1 building block in the photocatalytic hydrocarboxylation of alkenes, providing a path for the domino valorization of CO2 and waste towards bulk and fine chemical synthesis.