The development is a breakthrough in the bid to replace platinum, a rare and precious metal, in these processes. The results of this major development, in terms of the future of a more competitive hydrogen market, are presented in an article due for publication in Science.

Of all the new energy technologies, the use of hydrogen as an energy vector is an attractive solution. The hydrogen power sector cannot develop, however, unless two key steps can be controlled: first, the mass production of hydrogen by water electrolysis in electrolysers, and second, the use of hydrogen in fuel cells to supply energy thanks to the oxidation of the hydrogen.

At present, these processes require the use of platinum as a catalyst (substance that speeds up a chemical reaction). This metal is, however, extremely rare (terrestrial abundance of 5ppm, equivalent to that of gold) and, therefore, extremely expensive. Replacing platinum thanks to the development of efficient catalysts containing only elements that are found in abundance and are cheap is thus a major challenge for the future of the hydrogen power sector.

Research currently being carried out to replace platinum with cheap, abundant metals draws its inspiration from chemical processes at work in certain living organisms. Such organisms have fascinating enzyme systems, called hydrogenases, and make exclusive use of abundant metals such as iron and nickel, which enable them to use hydrogen as a source of energy or to produce it from water.

These enzymes are a unique source of inspiration for the chemist interested in synthesizing nickel- and iron-based compounds, structurally analogous to hydrogenases, thus developing new catalysts. This is known as bio-inspired chemistry.

However, for their use in technological solutions, the electrodes must be coated in very large amounts of these synthetic catalysts, just as for platinum. This implies a need for a large available surface, something not provided by conventional materials.

Thanks to their geometry, which makes it possible to considerably increase the potential bonding surface for the catalyst, as well as their high electrical conductivity, carbon nanotubes afford a solution for overcoming this difficulty.

In this study, the researchers successfully immobilized one of these bio-inspired, nickel-based catalysts on carbon nanotubes using a covalently bonded graft. The material obtained show promising catalytic activity for both the production and the use of hydrogen.

It also proves extremely stable and capable of functioning in a highly acidic medium, making it compatible with proton exchange membranes, used more or less universally in low temperature fuel cells. The development of this new material is another step forward in the race to improve hydrogen power technology.

V. Artero/CEA
Diagram showing the structure of the electrocatalytic material made up of carbon nanotubes on which a bio-inspired catalyst has been grafted.
Box : structures of the active sites of the hydrogenases that inspired the design for the catalyst.

Reference :
From hydrogenases to noble-metal free catalytic nanomaterials for H2 production and uptake hydrogen.
Le Goff A., Artero V., Jousselme B., Dinh Tran P., Guillet N., Métayé R., Fihri A., Palacin S., Fontecave M., (2009), Science, in press.