Abstract
Results of Grand Canonical Monte Carlo (GCMC) simulations of hydrogen storage at 303 K in ordered mesoporous carbons (OMCs) which are inverse replicas of cubic Im3¯m silica are presented. Of the ones investigated here, the highest gravimetric total storage of hydrogen (ca. 2 wt% at P = 22 MPa and 303 K) was observed for the OMC replica of the cubic Im3¯m material which was characterized by the largest lattice parameter and internal pore radius of the carbon sphere (a = 9.98 nm and Rint ≈ 3.0 nm). However, the corresponding volumetric density of hydrogen did not exceed 17 kg H2/m3. The highest excess storage was observed for a threshold value given approximately by a ≈ 7.98 nm and Rint ≈ 2.4 nm. Above this value, the excess storage and volumetric density of hydrogen did not change.
The adsorption was dominated by the bulk storage, with the adsorbent serving as a tank whose storage properties were governed by the available space for hydrogen molecules (bulk storage) and not by physical adsorption (i.e. densification of the supercritical fluid on the walls of the porous material). The calculated average value for hydrogen adsorption in internal spaces was twice as high as in the internal spaces of the spherical cavities, i.e. in the lattice parameter range of the Im3¯m OMC replicas that were studied experimentally at 303 K.
Our calculations indicate that the calculated maximum gravimetric weight per cent and volumetric density of hydrogen lay well below the target of 2010 for 6.0 wt% and 45 kg H2/m3 indicated by the United States Department of Energy. The storage of hydrogen at 303 K and P < 22 MPa in the OMC replicas of the cubic Im3¯m silica was effective against compression of the hydrogen fluid. However, it was not sufficiently effective to justify the application of these materials for the development of fuel cells for the automobile industry.