# Enzymatic Flow Electrolyzer for CO2 and Waste Comproportionation to Formate and Its Use in Photocatalytic Alkene Hydrocarboxylation

## TL;DR

A new flow electrolyzer converts CO2 and waste into formate efficiently, which is then used to make chemicals through photocatalysis.

## Contribution

A semiartificial flow electrolyzer using immobilized formate dehydrogenase enables efficient CO2 and waste conversion to formate for downstream chemical synthesis.

## Key findings

- The enzymatic flow electrolyzer achieved an initial faradaic efficiency of almost 200% toward formate.
- The system operated at a low voltage of −1.5 V for 122 hours and converted CO2 with a maximum yield of 18%.
- Electrogenerated formate was successfully used in the photocatalytic hydrocarboxylation of styrene to phenylpropanoic acid.

## Abstract

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.

A flow electrolyzer employing formate dehydrogenase on a porous TiO2‐carbon felt cathode is developed for paired electrolysis of CO2 and waste (plastic and biomass) to produce formate. The electrolyzer operates with an initial cell faradaic efficiency toward formate of almost 200% at a low cell voltage of −1.5 V, which also enables bias‐free operation with a commercial solar cell. The electrogenerated formate is used directly for photocatalytic carbon chain extension of styrene to phenylpropanoic acid.