Investigating the enzymatic CO2 reduction to formate with electrochemical NADH regeneration in batch and semi-continuous operations

Abstract The enzymatic production of formate from CO2 with the immobilized NADH-dependent formate dehydrogenase (FDH) on the activated electrospun polystyrene nanofibers (EPSNF) was investigated to develop a sustainable process for CO2 reduction. Direct electrochemical regeneration on a Cu foam electrode was employed to supply the reaction with the reduced cofactor (NADH). The formate production was studied in two modes of batch and semi-continuous operations with the cofactor recycle. Results indicated that the regenerated cofactor concentrations in both systems were nearly identical (0.5 mM) which ensured the desirable activity of the immobilized enzyme. This showed that the electrochemical regeneration system was effective even in the semi-continuous operation. Although the cumulative formate concentration in the batch operation was higher, the total amounts of the produced formate were higher for the semi-continuous mode for more than 42% which was justified by the fact that the lower formate concentration in the semi-continuous mode would be favorable to the progress of the enzymatic CO2 to formate conversion. Finally, it was concluded that the proposed semi-continuous process in this work could be considered as a promising process for the enzymatic CO2 conversion.