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 m(2) 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 N-2 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, alpha, and beta) 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 alpha and beta parameters are related to the average micropore size and total pore volume, respectively. alpha and beta 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.

Automated summary

This study investigated hydrogen adsorption on six commercial activated carbons under different temperature and pressure conditions. The authors found that the use of nonlocal density functional theory provided a more accurate prediction of hydrogen adsorption capacity. The relationship between hydrogen adsorption capacity and surface properties of activated carbons was established, and different parameters were identified for evaluating the best activated carbon for hydrogen storage or compression.