| With a growing world population and an increasing standard of living, the world will run out of fossil fuels. In addition, fossil fuels have an adverse effect on the earth environment. It is urgent to quest abundant, environmentally benign, renewable, safe and cost-effective energy. Hydrogen is considered as a promising fuel in the future.Unfortunately, it has to be produced from water or other compounds, so it is not an energy source but an energy carrier. Large-scale application of hydrogen energy have to solve it′s production and storage question. Among these, storage of hydrogen is the most difficult hurdle. The common high pressure tanks and cryogenic tanks are expensive, furthermore, the energy density of hydrogen of these forms is only 4.4 and8.4 MJ/L,respectively,which is inferior to the energy density of gasline of 31.6MJ/L.The ideal method is to store hydrogen in solid materials, which include physisorption and chemisorption. The Department of Energy of American′s ultimate storage targets require gravimentric and volumetric density of 7.5 wt% and 70 g/L,the operating temperature between-40—85℃,a pressure of 120 bar and the fueling time of 6 kg hydrogen less than 3 min. In addition, the storage system should be safe,durable and cost-effective.The materials for physisorption are high specific surface porous materials, such as activated carbon, nanostructure materials and metal-organic frameworks, they exhibit promising hydrogen storage capacities at 77 K, but less than 1 wt% of hydrogen can be stored at 298 K. The reason for such a disappointing hydrogen storage capacity at 298 K is the binding energy(less than 10 kJ/mol) is too weak.Scientists have different opinions on the appropriate binding energy for physisorption of hydrogen. This paper analyze the optimum conditions based on Langmuir adsorption isotherm. For maximum delivery between P=50-100 bar and P1=1.5 bar at ambient temperature,an adsorption enthalpy change about-33.5 kJ/mol is desired. |
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