# Decoupling Charge Carrier Electroreduction and Enzymatic CO2 Conversion to Formate Using a Dual-Cell Flow Reactor System

## TL;DR

A dual-cell system efficiently converts CO2 to formic acid using enzymes, avoiding unwanted reactions and improving long-term performance.

## Contribution

A dual-cell flow reactor system is introduced to decouple electroreduction and enzymatic CO2 conversion, enhancing formate production and stability.

## Key findings

- The system produced 25 mM of formate with over 50% Coulombic efficiency.
- Long-term stability was achieved using pH control and packed bed reactor configurations.
- The dual-cell system outperformed batch cells in formate production quantity.

## Abstract

With an efficient
atom economy, low activation energy, and valuable
applications for fuel cells and hydrogen storage, formic acid (FA)
is a useful fuel product to convert CO2 and reduce emissions.
Although metal catalysts are typically used for this conversion, unwanted
side reactions remain a concern, particularly when products are attempted
to be recovered long-term. In this study, an enzymatic catalyst is
used to enable the selective conversion of CO2 to FA, as
a formate ion. A dual-cell flow reactor system is used to first reduce
a charge mediator electrochemically (reduction cell), which then activates
a catalyst to selectively convert CO2 to formate (production
cell). This approach minimizes enzyme degradation by avoiding direct
contact with increased voltages and improves the quantity of formate
produced. The system produced 25 mM of formate and reached over 50%
Coulombic efficiency. The larger volume of this dual-cell system increases
the quantity of formate produced beyond that of a batch cell. Additional
design configurations are employed, including a pH control pump to
maintain catalyst activity and a packed bed reactor to improve contact
of the charge carrier with the catalyst. Both configurations retained
higher production and efficiency long-term (∼168 h). The results
highlight the challenges of developing a system where many parameters
play a role in optimizing performance. Nevertheless, the ability of
the system to produce formate from CO2 demonstrates the
potential to improve upon this configuration for a variety of electrochemical
CO2 conversion applications.