Cryogenic temperatures, hydrogen adsorption

Also, there are theoretical simulations predicted a high adsorption selectivity (up to 100000 at 20 K) of heavy hydrogen isotopes (tritium, deuterium) from isotopes mixtures in nanotubes at low temperatures [7, 8], But there is no experimental information about adsorption isotherms (except natural isotopic composition hydrogen) and separation factors of the hydrogen isotopic modifications on nanoporous materials at cryogenic temperatures in the literature, and it obtaining has doubtless interest. 

The hydrogen storage values of PIMs and HCPs are still smaller than for many porous carbon samples. However, PIMs and HCPs have only recently been investigated for H2 adsorption and further modifications of these materials can lead to an enhancement of their hydrogen storage capacity at cryogenic temperatures. 

There are other experiments showing high levels of hydrogen adsorption on SWNTs at cryogenic temperatures, typically around 77 K [4, 29-31], but these conditions are not particularly relevant to vehicular fuel cells. 

As for pore volume of sorbent, its correlation with storage capacity is more apparent at cryogenic temperatures, e.g., 77 K. This is because at cryogenic temperatures, the hydrogen adsorption on porous carbon is more dominated by partial condensation of H2 molecules into its microporosity. Linear relationships between storage capacity at 77 K and pore volume have been observed on microporous carbon [50], mesoporous carbon [51], and various carbon sorbents [36,37]. As presented in Figure 6.4, a linear relationship can be clearly seen for amount of hydrogen adsorbed at 77 K in ACs, CNTs, and nanofibers versus their total micropore volume and narrow micropore volume. 

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