Nanostructured Materials for Hydrogen Storage and Generation
Hydrogen is considered as the fuel of the future. It is the cleanest fuel since it does not generate any harmful product when used, with water as the only product. Two key issues in using hydrogen as a viable fuel are its storage and generation.
Hydrogen storage is the bottleneck for on-board vehicle application. In order to achieve the FreedomCar targets in 2010 proposed by Department of Energy, the gravimetric hydrogen density should be ~ 6 mass%, and be able to be operated at ambient conditions (< 373 K and 2 atm). It has been demonstrated that the safest way to store hydrogen is solid state material. Currently, there are three different hydrogen storage materials, metal hydrides, carbon based materials such as carbon nanotubes, and complex hydrides, that have been shown to be promising for hydrogen storage. In order to improve the properties of hydrogen storage materials, there are basically two general methodologies: either to find novel materials, especially the complex hydride, or to tailor the microstructures of existing storage materials, especially into nanostructures. Our interests are in the second one, tailoring the microstructure of metal hydride to improve its hydrogen sorption performance, e.g. to improve the thermodynamics and kinetics of hydrogen sorption, and reversibility.
One of the most attractive methods for hydrogen generation is photodecomposition of water using solar light based on the reaction of H2O + light ─> H2 + ½O2. Both solar light and water are relatively abundant and inexpensive; the reaction is environmentally friendly. However, this reaction is very endothermic and direct photodecomposition of water using soar energy in the near UV and visible region for hydrogen generation is not feasible. Fortunately, this reaction can be made possible with photocatalysts or photoelectrochemical cells (PEC). In photoelectrochemical cells with common photoelectrodes such as TiO2 providing a maximal photovoltage of about 0.8 V, an external bias voltage of about 0.4 V is still required for this reaction that requires a minimum of 1.23 eV electromotive force. This external bias can in principle be supplied by a photovoltaic cell (PVC). We are interested in developing a photoelectrochemical cell (PEC) integrated directly with a photovoltaic cell (PVC) for hydrogen generation from water decompostionusing solar light.