In this study, three types of carbon fibres were used, they were ex-polyacrylonitrile carbon fibres with high bulk modulus, ex-polyacrylonitrile fibres with high strength, and vapour grown carbon fibres. All the samples were subjected to a hydrogen adsorption process at room temperature in an over-pressured atmosphere of 25 bars. The adsorption process was monitored through electrical resistivity measurements. As conditioning of the fibres, a chemical activation by acid etching followed by γ-ray irradiation with 60Co radioisotopes was performed. The surface energy was determined by means of the sessile drop test. Both conditioning treatments are supplementary;the chemical activation works on the outer surface and the γ-irradiation works in the bulk material as well. Apparently, the most significant parameter for hydrogen storage is the crystallite size. From this point of view, the most convenient materials are those with small grain size because hydrogen is accumulated mainly in the grain boundaries.
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