Hydrogen absorption process into graphite and carbon materials

In order to estimate bulk hydrogen retention and recycling in graphite and carbon materials, molecular hydrogen absorption has been studied. Hydrogen absorption rates significantly depend on, samples which arise from grain si ze, trap concentration and so on. Absorption rate constants differ between the cases of low and high pressures. Trapping has a strong influence, espec ially in the low pressure range. Oxidation of graphite reduces hydrogen ret ention and enhances the absorption rate. This suggests that oxygen in graph ite does not behave as trapping sites for hydrogen. Activation energies for apparent diffusion for H-2 and D-2 are determined to be 153 and 158 kJ/mol . They are smaller than those energies determined from desorption measureme nts. (C) 2000 Elsevier Science B.V. All rights reserved.