Hydrogen gas is a non-toxic and completely environment-friendly energy source and has been seen as a great alternative to various traditional energy sources for years in developed countries. Using hydrogen as an energy source can be the much desired solution to address the growing demand for energy and slow down global climate change. Moreover, hydrogen gas can easily be produced from a number of resources including renewable resources (e.g. biomass and water) and fossil resources (e.g. coal and gas).
Being an ultra-light gas, a very small weight of hydrogen contains a huge amount of energy compared to other energy sources; but by volume it contains much lower energy compared to petrol and other sources, and hence arises the main obstacle to shift into a hydrogen-economy. Hydrogen storage is the key technology to build the efficient and promising hydrogen and fuel cell power technologies which will make it possible to store hydrogen in a light and compact form.
At present three technologies are available for on-board hydrogen storage -
The material-based storage technology is a more promising technology compared to the other available technologies which refers to the storage of hydrogen gas within the structure or on the surface of some advanced materials like carbon-based materials, metal hydrides etc. To be accepted as a widespread alternative fuel, hydrogen gas must be stored in the fuel tank of a car in sufficient amount enabling the car to travel more than 300 miles with a single fill.
Sorption of hydrogen atoms or molecules to other elements in a potential storage material may store huge quantities of hydrogen in smaller volumes, though additional research is required the identify a suitable material that is safe, affordable, can be produced easily in huge quantities, can store large amounts of hydrogen in a light, compact form, and can be refueled rapidly.
A number of characteristics, such as the life span of the material, the surface area of the material, the reversibility of the uptake and release of hydrogen, the porosity of the material, toxicity, overall safety, efficiency and cost of the potential storage material should be well understood to identify a suitable storage material. Therefore material characterization is vitally important for the research and development of storage materials and storage technology as well.
Porosity is a vitally important characteristic for a potential storage material - microporous materials are preferably considered for physisorbed molecular hydrogen storage to mesoporous and macroporous materials. Storage materials within the ultramicroporous subcategory is excellent in increasing the density of adsorbed hydrogen at any given temperature and pressure with its extraordinary (<0.7 nm) pore dimension which is close to the size of a single hydrogen molecule.
A novel porous material having high surface area can bring a revolution in the field of material based hydrogen storage. The internal surface areas of the existing porous framework materials can be extended through their structural modification and thus their hydrogen storage capacity can be increased up to three times under low pressure storage conditions.
Sorption is another major characteristic of a potential storage material which takes place only in micropores and affects its overall storage capacity to a considerable extent. Recent studies are searching for a high-capacity and reversibly sorbent materials which is useable at room temperature and can store hydrogen very efficiently.
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