Evaluation of single chamber electrochemical reduction of CO2 to formate for application under biocompatible conditions

The electrochemical CO₂ reduction reaction (eCO₂RR) facilitates high rates and yields for the selective production of formate, a quintessential C1-compound that can serve as a valuable carbon and energy source for biosynthesis. The use of double-chamber (DC) electrochemical cells with membranes is deemed essential to avoid mixing of electrochemical products (i.e. anodic oxygen and cathodic formate) and thus cross-reactions that lower yields, Faradaic efficiency (FE) and effective rate. However, single-chamber (SC) setups for eCO₂RR can be more suitable to combine with bioprocesses. This work comprehensively evaluates, using different experimental set-ups, the conditions under which SC operation can obtain results comparable to DC systems. At a 50 mL scale, under biocompatible conditions, formate production in the SC setup achieved a 14 % reduction in the production rate (146 mg L⁻¹ h⁻¹ for SC and 170 mg L⁻¹ h⁻¹ for DC) and a 15 % decrease in FE (72.2 % in SC and 84.7 % in DC). The highest formate concentration produced in 24 h SC experiments was 1.8 g·L⁻¹ with FE of 41 %, a concentration appropriate for fermentation processes. The SC operation of eCO₂RR to formate without a membrane could reduce energy losses and capital costs, although at the cost of an expected reduction in rate and FE.