Fuel cells represent an efficient method for chemical energy conversion and possess substantial application potential in space due, to their clean operation and their compactness. At present, NASA develops, in co-operation with US-American companies, PEM (Polymer Electrolyte Membrane) fuel cell modules, which should be available for space qualification procedures in 2005.
Applications for Fuel Cells and What Improvements Nanotechnology Can Offer
Application of fuel cells is an objective particularly pursued within the range of re-usable space transporters. But fuel cells, in principle, represent alternatives for batteries in many other space applications. For example, SOFC fuel cells could be used for the electrochemical oxygen production in manned space stations, or for the in-situ resource production on other planets. Nanotechnology offers different possibilities to increase the conversion efficiencies of fuel cells, in particular, within the ranges of catalysts, membranes and hydrogen storage, which in many cases is critical for the employment of fuel cell technology in space.
Nanotechnology Catalysts Might Improve the Efficiency of Direct Methanol Fuel Cells
Precious metal nanoparticles improve the high-efficient production of hydrogen in direct methanol fuel cells. This type of fuel cell needs liquid methanol as fuel, from which the hydrogen is generated by a catalyst. The main obstacle here is the poisoning of the catalysts through by-products like carbon monoxide. Improved nanotechnological catalysts, which are more insensitive against carbon-containing gases, could contribute to a solution of this problem.
Nanotechnology Techniques for Improving Solid Oxide Fuel Cells (SOFC)
Also, the electrolyte of Polymer Electrolyte Membrane (PEM) fuel cells can be improved by nanoparticles. For example, the Max-Planck Institute (MPI) for solid state research in Stuttgart, acting in co-operation with MPI for polymer research in Mainz, developed custom-made polymer membranes, with densely packed nanoparticles, which are immobilized on the surface of imidazole molecules and provide an optimized proton transportation. For Solid Oxide Fuel Cells (SOFC), ceramic nanopowders (e.g. yttrium stabilized zirconium, YSZ) are used for the production of solid electrolyte membranes, with improved ionic conductivity and better thermal stability.
Nanomaterials Can Offer an Efficient Method for Hydrogen Storage for Mobile Application
One of the main obstacles to the implementation of fuel cells for mobile application is, at present, still the technologically and economically reasonable storage of the fuel (especially hydrogen). Nanomaterials, due to their increased active surface area, basically possess potential to be a lightweight high-efficient storage media for hydrogen.
Material Types Used for Hydrogen Storage
With regard to operating conditions (temperature, pressure), different material types should be taken into consideration. Nanocrystalline light metal hydride particles from magnesium-nickel alloys are suitable for operating temperatures up to 300°C, and LaNi5 alloys for low temperature hydrogen storage up to 80°C. Also, for carbon nanotube materials or alkali metal doped graphite nanofibers, high hydrogen absorption capacities are reported, but were partly not reproducible.