Lattice gas model for H₂ adsorption in nanoporous zinc hexacyanometallates

Zinc hexacyanometallates Zn₃A₂[M(CN) ₆]₂ with different exchangeable alkaline cations A ⁺ and framework transition metals M constitute an excellent model system to study H₂ adsorption in nanoporous solids. A lattice gas approach, based on experimental data and simple considerations on the position and energies of adsorption sites, is proposed. Coverage and adsorption enthalpies are calculated and compared with experimental results. The interplay of three necessary conditions for H₂ storage in porous solids-free volume to accommodate guest molecules, charge centers to bind them, and fast diffusion during adsorption or desorption-is discussed.