Pore wall corrugation effect on the dynamics of adsorbed H-2 studied by in situ quasi-elastic neutron scattering: Observation of two timescaled diffusion

The self-diffusion mechanisms for adsorbed H2 in different porous structures are investigated with in situ quasielastic neutron scattering method at a temperature range from 50 K to 100 K and at various H-2 loadings. The porous structures of the carbon materials have been characterized by sorption analysis with four different gases and the results are correlated with previous in-depth analysis with small-angle neutron scattering method. Thus, an investigation discussing the effect of pore shape and size on the nature of adsorbed H-2 self-diffusion is performed. It is shown that H-2 adsorbed in nanometer-scale pores is self-diffusing in two distinguishable timescales. The effect of the pore, pore wall shape and corrugation on the fraction of confined and more mobile H-2 is determined and analyzed. The increased corrugation of the pore walls is shown to have a stronger confining effect on the H-2 motions. The difference of self-diffusional properties of the two H-2 components are shown to be smaller when adsorbed in smoother-walled pores. This is attributed to the pore wall corrugation effect on the homogeneity of formed adsorbed layers.