Hydrogen Storage by Adsorption onto Different Activated Carbons

The objective of this work was to evaluate the hydrogen storage capacities of various activated carbon materials in form of granules, powders, fibers and clothes under cryogenic and ambient temperature conditions (77K 293K), at pressures up to 30Bar. The experimental data were analyzed for carbon samples covering a wide range of BET surfaces and microporous volumes. At 293K, the storage capacities of all the materials tested were found to be very low, and to result mainly from compression of the gas within the external voidage of the bulk solid sample and the internal porous volume of the material. Under these conditions, the storage capacity varies linearly with the pressure increase. At 77K, the contribution of physisorption becomes significant and was shown to represent nearly 60% of the maximum storage capacity measured à 20Bar. The experimental set of data enabled to propose a model to predict the weight of hydrogen stored in the carbonaceous sample. This model assumes the superposition of the two phenomena : physisorption within the material's micropores and gas compression in the external and internal voidage of the sample The model was deduced from the Langmuir equation and a non ideal gas law. According to this model, the maximum weight percentage of hydrogen that could be stored in a tank filled with a material having a BET surface equals to 2600m/g and a bulk density of 200 kg.m would be as high as 9% in weight at 20Bar.