A Step Forward in Understanding the Hydrogen Adsorption and Compression on Activated Carbons.

Hydrogen adsorption on activated carbons (ACs) is a promising alternative to compression and liquefaction for storing hydrogen. Herein, we have studied hydrogen adsorption on six commercial ACs (CACs) with surface areas ranging from 996 to 2216 m2 g-1 in a temperature range of 77 to 273 K and pressures up to 15 MPa. Excess hydrogen adsorption capacities of 2.3 to 5.8 wt % were obtained at 77 K and 4 MPa. We demonstrated that, contrary to what is normally done, hydrogen capacity is more accurately predicted by the surface area determined by the nonlocal density functional theory method applied to N2 and CO2 adsorption data than by the Brunauer-Emmett-Teller (BET) area. The modified Dubinin-Astakhov (MDA) equation was used to fit the experimental adsorption data, and the relationship between the MDA parameters (nmax, Va, α, and β) and the textural properties of the CACs was determined for the first time. We concluded that the nmax and Va parameters are related to the BET area, while the α and β parameters are related to the average micropore size and total pore volume, respectively. α and β were used to evaluate the enthalpy and entropy of adsorption and we show that these parameters can be used to assess the best carbon for hydrogen storage or compression.