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 (n_max, V_a, α, and β) and the textural properties of the CACs was determined for the first time. We concluded that the n_max and V_a 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.