Adsorption of hydrogen on activated carbons and carbon nanostructures

6 Adsorption of hydrogen on activated carbons and carbon nanostructures 

6 (a) Hydrogen excess adsorption in gram H2 per kilogram of activated carbon from 77 to 295 K. Data from P. Benard and R. Chahine, Hydrogen Energy Progress X, p 1121 (1998). (b) Low-temperature isotherms from 30 to 77 K compared to the room temperature isotherm. Data from J. Michelsen, R. Chahine, A. Tessier and D. Cossement (unpublished, 2007). 

The contribution of the pores to the gravimetric density is obtained by multiplying equation (10.23) by the bulk gas density of the adsorbent. This yields a contribution of  

The high-pressure, low-temperature adsorbed density of hydrogen on activated carbon seems to correlate linearly with the micropore volume and the specific surface area of the adsorbent. The density of hydrogen inside the micropores can be estimated from the ratio of the excess density adsorbed to the micropore volume, to which must be added the contribution of the bulk phase in the micropores. This yields a value of 62mg/cm, suggesting that at 77 K and 35 bar, the density of hydrogen inside the micropore is already close to that of liquid hydrogen. Similar values (from 61 to 71 mg/ cm ) are obtained for other activated carbon adsorbents with different pore volumes and specific surfaces.  

As can be seen from Fig. 10.6, the storage capacity is extremely sensitive to temperature. The maximum density that can be stored as a cryoadsorbed gas occurs close the critical point. At 35 K and 0.6 bar, the contribution of the excess adsorbed density to storage is 9.5 wt%. 

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