Isosteric Heat of Potential Confinement in the Hydrogen Storage Material

Abstract

In the hydrogen storage problem, if an attractive potential well is formed inside the void space of porous materials, the storage gas density is expected to increase significantly compared to the H2 gas density outside the material. Actually, the overall H2 density inside the material is enhanced basically by a Boltzmann factor of exp[[Formula: see text]/[Formula: see text]] where U ([Formula: see text][Formula: see text]0) is some averaged potential energy. Corresponding to this negative potential energy, latent heat is released in the H2 gas confinement process. We theoretically investigate the energetics involved during the H2 storage in the potential well and, from the equilibrium thermodynamic principles, we derive a formalism for the isosteric heat of potential confinement of the H2 gas. Since the gas density inside the potential well increases tremendously, the van der Waals equation is adopted to describe the nonideal gas behavior of H2. We compare our results to the well-known expression for the isosteric heat of adsorption where, unlike our case, the molecules are bound to specific adsorption sites in the material.