Effect of porous texture on hydrogen adsorption in activated carbons

Physisorption-based hydrogen (H 2) storage in microporous carbons has a trade-off between adsorption capacity and adsorption enthalpy [5]. Conceptually, this problem is best illustrated in terms of the ideal slit pore formed from two parallel, semi-infinite graphite slabs. Packing density is maximized when the pore width is several times larger than the diameter of the H 2 molecule, since it permits the formation of several hydrogen monolayers within the pore [16]. At supercritical temperatures, however, condensation within pores does not occur. Characteristic H 2 adsorption enthalpies associated with large slit pores therefore approach the enthalpy of H 2 adsorption on carbon, typically measured between 4 kJ mol −1 to 6 kJ mol −1 [15, 121]. With smaller pores, the adsorption enthalpy increases due to the overlap of potentials fields from each face of the pore. The packing density begins to decrease, though, when the pore is no longer wide enough to accommodate two H 2 monolayers. Ab initio calculations of hydrogen adsorption in ideal slit pore carbons Portions of this chapter were published in the article: