Does anyone here work on hydrogen storage via physisorption on metal-decorated substrates? There are a few things that I would like to clarify: 1. What exactly is the physical origin of the 0.2 to 0.6 eV adsorption energy requirement for hydrogen molecules? 2. As adding more hydrogen molecules will in general decrease the adsorption capacity of the adsorbing substrate, what criteria is usually employed in order to say that for example, only three hydrogen molecules can be adsorbed?
Ad. 1.
0.2 to 0.6 eV per molecule transfers to ca. 19 to 59 kJ per mole.
A nice discussion of the energetic considerations of adsorptive hydrogen storage in porous materials has been presented in:
S. K. Bhatia, A. L. Myers, Optimum Conditions for Adsorptive Storage, Langmuir, 22 (2006) 1688-1700.
I think it could also be extended to the metal surface.
Hi,
From the van't Hoff equation, an enthalpy of desorption around 35 kJ/mol H2 in a chemisorbed system (such as transitional metal hydrides) will result in 10 atm equilibrium pressure at 320 K. For gases such as hydrogen and neon physisorbed on graphite and carbon nanotube bundles, the isosteric heat at monolayer completion is around 300- 400 K per atom (in units of Boltzmann constant) - approx 2.5-3.3 kJ/mol H2. The purified nanotubes had less than 3% Fe catalyst and weren't coated/ decorated with a metal overlayer.
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