Anisotropic diffusion of hydrogen in nanoporous carbons

It is accepted that hydrogen transport capacity through carbons depends on the anisotropy of the empty spaces that constitute their porous structure. However, very little is known about this relationship. Computational simulation is an excellent tool to accomplish this kind of studies. Simulation requires digital representations of materials and a model describing the interaction potential among the gas molecules and the solids surfaces. In this work, it is proposed to use the analytical solutions of the truncated pore problem for modeling the potentials, and an immiscible lattice gas for obtaining the representations. The degree of anisotropy was quantified by using the mean intercept length method. The adsorption isotherms and the self-diffusion coefficients in the three orthogonal directions were found by the grand canonical and kinetic Monte Carlo methods, respectively. The results suggest the existence of a gas pressure at which a molecular saturation threshold (Ps) is reached. Ps determines if the degree of anisotropy is or not a representative variable of diffusive transport. For P ≤ Ps, the degree of anisotropy favors the molecular mobility. When P > Ps, the degree of anisotropy loses influence on mobility.