Better catalysts for solar-driven hydrogen producing devices: electrochemical studies on novel and highly efficient [FeFe]-hydrogenases immobilised on optically transparent TiO2 electrodes

A novel hyperactive [FeFe]-hydrogenase was cloned from a C. perfringens selected in a pilot plant efficiently producing biohydrogen from waste and heterologously expressed in E.coli. The enzyme was immobilized by adsorption on anatase TiO2 electrodes either of 250 nm (15-20 nm particle size) or 4 microns thickness (>100 nm particle size, standard material employed in dye sensitized TiO2 based photovoltaics cells) provided by Solaronix (CH). Immobilization and electron transfer without any mediator was demonstrated between the C. perfringens hydrogenase and TiO2 since a catalytic currents both at higher potentials (hydrogen consumption) and lower potentials (hydrogen production) was recorded. The current densities measured at lower potential where hydrogen production occurs were in the order of 0.6 mA/cm2, even at low concentration of immobilised enzyme, showing an extremely high efficiency of this catalyst on the considered transparent electrode. Measured currents were compared with the previously reported [1] values for CaHydA on TiO2, demonstrating that the novel enzyme is even more promising than CaHydA for employment in biocathodes that can be applied in solar-driven devices for hydrogen production. Also hydrogen gas was produced by setting the electrode at a fixed negative potential in a sealed electrochemical cell. The headspace composition was determined by gas chromatographic analysis, demonstrating that hydrogen gas is produced by the immobilized [FeFe]-hydrogenase.