Effect of long range van der Waals interactions on hydrogen storage capacity and heat of adsorption in large pore silicas

The low temperature hydrogen adsorption capacity of mesopores silica aerogel was investigated and compared with that of other large pore silica based materials (MCM-41, HMS) within a range of surface area and large (2 nm) to very large (20 nm) pore sizes. The hydrogen uptake of the aerogel measured at pressure of 1 bar and a temperature of 77 K is around 2.5 times lower than that of MCM-41, although it has a comparable specific surface area (just 30% smaller). The explanation found is the relation between lower hydrogen heat of adsorption and larger pore size for the investigated materials, which leads to higher surface coverage in the smaller pores.