Novel artificial ionic cofactors for efficient electro-enzymatic conversion of CO2 to formic acid

The low yield of enzymatic conversion of CO2 to formic acid as well as the high cost and instability of using the natural cofactor (NADH) hamper the large-scale application of the CO2 enzymatic utilization. To address these issues and to improve the production of formic acid, six bipyridinium-based artificial cofactors were developed for the enzymatic conversion of CO2 and further integrated with the electrocatalytic regeneration of the cofactors for the formic acid production. All of them did show a higher catalytic performance compared to NADH. Particularly, 1,1′-bis(2-(dimethylamino)ethyl)-4,4′-bipyridinium bromine did exhibit the highest catalytic performance with a high formic acid concentration of 4.76 mM in 60 min, which is 47 times higher than that of the natural cofactor NADH and is also currently the highest performance among the reported artificial cofactors in literature. Thermodynamic analysis, electrochemical investigations, and molecular dynamics simulations were performed to clarify the structure-energy relationship of the functional bipyridinium-based salts and to rationalize how it is affected by the different functional groups. This study gives a deep insight into the role of artificial cofactors in enzymatic reactions and can clearly promote the development of novel bioelectrochemical conversion of CO2.