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Romain Métayé

Toward hydrogen photoproduction by immobilized bio-inspired catalysts

Published on 13 October 2010

Thesis presented on Octobre 13, 2010

The development of hydrogen production processes based on renewable resources such as the sun as an energy source and water as the source of proton is the first step in the creation of a carbon free hydrogen economy. This thesis project is inspired by the capacity of some photosynthetic microorganisms to generate hydrogen under solar irradiation in water. This work of thesis describes more particularly the fabrication and characterization of a photoelectrode for proton reduction in aqueous medium, under visible light. This electrode associates a photocathode and a catalyst either immobilized at the surface or in solution.
The photocathode is a multilayered device based on the sensitization of a p-type semiconductor nickel oxide thin film. The dye used in this work is the ruthenium(II) trisbipyridine, that was chemically modified with diazonium functions and grafted by electroreduction. The ability of this photocathode to transfer electrons under visible light to an acceptor in solution (aqueous and organic) was demonstrated by the generation of a photocurrent. Hydrogen photoproduction was firstly evidenced under visible light in an aqueous solution containing platinum catalyst. Two noble metal free bio-inspired catalysts for proton reduction (a di-iron complex and a nickel complex) were also selected and chemically modified to enable their grafting on various electrodes. Whereas the diiron modified electrodes are quickly deactivated during electrolysis at low potential, the association of a carbon nanotube-based electrode and nickel complex revealed to be exceptionally active and stable for proton reduction in aqueous medium. The grafting of the nickel complex on a photocathode was also achieved; however the current densities obtained under illumination were too low for the detection of the photoproduced hydrogen.