On the stability of electrochemical CO2 reduction reaction to formate at indium electrodes at biocompatible conditions

In a circular economy, carbon dioxide (CO2) has to serve as feedstock that can be utilized by electrochemical CO2 reduction reaction (eCO2RR). Using eCO2RR to C1-compounds such as formate (HCOO-) allows producing feed for microbial syntheses that generates value-added compounds. However, eCO2RR at biocompatible conditions is currently limited to short-term operation facing a gradual performance deterioration. Here, we evaluate the possible parameters affecting the stability of performance in terms of formate production rate (rHCOO- ) and coulombic efficiency (CE) of eCO2RR at indium during 72 h batch mode operation. Formate accumulated over time affected catholyte conductivity, but statistical analysis showed this did not have an immediate influence on the performance. However, both are key factors altering the actual cathode potential over time that in turn is leading to changes in rHCOO- (maximum deviation of & PLUSMN; 0.03 mmol h-1 cm-2 at the stable performance at each condition) and CE (maximum deviation & PLUSMN; 40% at stable performance at each condition). These effects were more significant after reaching certain formate concentration and catholyte conductivity (ca. 70 mM and 21 mS cm-1, respectively). These results highlight the potential obstacles needed to be considered and tackled in order to achieve stable rHCOO- and CE over a long-term eCO2RR operation. This study discusses how to overcome these obstacles from different operational perspectives.