Enzymatic electrosynthesis of formate through CO2 sequestration/reduction in a bioelectrochemical system (BES)

[Display omitted] •BES was operated using formate dehydrogenase for CO2 reduction to formic acid.•Cathodic reduction current was observed in CA at −0.8V and −1V but not at −0.4V.•Quasi-reversible redox peak observed at −1V, shows continuous electron transfer.•Higher productivity and columbic efficiency were observed at −1V operation.•Product saturation was observed within 45min of enzyme addition at cathode. Bioelectrochemical system (BES) was operated using the enzyme formate dehydrogenase as catalyst at cathode in its free form for the reduction of CO2 into formic acid. Electrosynthesis of formic acid was higher at an operational voltage of −1V vs. Ag/AgCl (9.37mgL−1 CO2) compared to operation at −0.8V (4.73mgL−1 CO2) which was strongly supported by the reduction catalytic current. Voltammograms also depicted a reversible redox peak throughout operation at −1V, indicating NAD+ recycling for proton transfer from the source to CO2. Saturation of the product was observed after 45min of enzyme addition and then reversibility commenced, depicting a lower and stable formic acid concentration throughout the subsequent time of operation. Stability of the enzyme activity after immobilization on the electrode and product yield will be studied further.