Reactivation of standard [NiFe]-hydrogenase and bioelectrochemical catalysis of proton reduction and hydrogen oxidation in a mediated-electron-transfer system.

Standard [NiFe]-hydrogenase from Desulfovibrio vulgaris Miyazaki F (DvMF-Hase) catalyzes the uptake and production of hydrogen (H) and is a promising biocatalyst for future energy devices. However, DvMF-Hase experiences oxidative inactivation under oxidative stress to generate Ni-A and Ni-B states. It takes a long time to reactivate the Ni-A state by chemical reduction, whereas the Ni-B state is quickly reactivated under reducing conditions. Oxidative inhibition limits the application of DvMF-Hase in practical devices. In this research, we constructed a mediated-electron-transfer system by co-immobilizing DvMF-Hase and a viologen redox polymer (VP) on electrodes. The system can avoid oxidative inactivation into the Ni-B state at high electrode potentials and rapidly reactivate the Ni-A state by electrochemical reduction of VP. H oxidation and H reduction were realized by adjusting the pH from a thermodynamic viewpoint. Using carbon felt as a working-electrode material, high current densities-up to (200 ± 70) and -(100 ± 9) mA cm for the H-oxidation and H-reduction reactions, respectively-were attained.