Electrochemical studies on a recombinant [FeFe]-hydrogenase as hydrogen producing catalyst

[FeFe]-hydrogenases are redox enzymes, efficient natural catalysts that can produce hydrogen gas from water when they are supplied with a source of low potential electrons. Several studies are undergoing to exploit their ability to produce such a valuable fuel. In order to drive the electrons directly into the enzyme, it is of particular interest the possibility of coupling them with electrodesIn this case, [FeFe]-hydrogenases can be used as powerful catalysts to replace expensive noble metals, such as platinum. The [FeFe]-hydrogenase CaHydA from the bacterium Clostridium acetobutylicum was recombinantly expressed in E. coli and affinity purified in the active form under strict anaerobic conditions. The purified enzyme is highly thermo stable and has a specific activity (for hydrogen production) of 50 µmol H2 • min-1 • mg protein-1. CaHydA was immobilized on anatase TiO2 electrodes, either by simple adsorption of the enzyme on the electrode surface or by entrapment in polymers. Immobilization and electron transfer without any mediator between CaHydA and TiO2 was demonstrated by the presence of catalytic currents both at higher potentials (hydrogen consumption) and lower potentials (hydrogen production). 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 with efficiencies of over 70%.. In conclusion, this work demonstrates the possibility to immobilize the [FeFe]-hydrogenase CaHydA on TiO2, with productive electron transfer. The resulting electrode is therefore a hydrogen evolving cathode that can be used in artificial devices.