Different approach to estimation of hydrogen-binding energy in nanospace-engineered activated carbons
Résumé
Binding energy between adsorbent and adsorbate strongly affects themechanism of adsorption. Porous systems are usually characterized by a distribution ofthis energy, which is not easy to determine experimentally. A coupled experimentalsimulationprocedure to estimate binding energy directly from experimentaladsorption isotherms is proposed. This new approach combines experimentalinformation (pore size distribution determined from nitrogen adsorption at 77 K)and numerical data (grand canonical Monte Carlo simulations of adsorption in pores)to explain an influence of binding energy on adsorption isotherms. The procedure hasbeen validated by analysis of hydrogen adsorption in a series of carbons activated withKOH:C ratio varying from 3 to 6. These carbons show high capacity of hydrogenstorage both at 80 and 303 K (115 gH2/kgC and 23 gH2/kgC at p = 100 bar,respectively, for carbon activated during 1 h at T = 790 C (T = 1361 K) with KOH:Cratio equal to 3, having the surface area above 2600 m2/g, 0.77 porosity, and largefraction (31%) of pores with average width below 1 nm). An additional energeticparameter has been introduced into the conventional fitting procedure to account for the distribution of adsorption energy inmeasured samples. The observed high consistency between experimental and simulated results validates/correlates thecharacterization procedures and proves the coherence and robustness of both the experimental results and the numericalsimulations.