In the case of hydrogen storage, it is essential that the materials have high densities to achieve high volumetric capacities. But it is also need to have low densities to achieve high mass capacities.
All is about optimisation. We already proved this for methane storage, see Fig. 10 and 11 of the attached Energy & Fuel paper, and Fig. 8 of the attached Carbon paper.
In the case of hydrogen, it is the same. You first have to increase as much as possible the amount of relevant pores (i.e., getting the most suitable porosity), and then see how to pack your grains of porous carbons in an as compact way as possible.
Alain
Playing with the concentration of intial reactant may also help.
For example - For example for the synthesis of carbon aerogel derived from Resorcinal-Formaldehyde(RF). The ratio of R:F and R:catalyst mainly decides the density and hence porosity od carbon aerogel.
There are figures of merit that you should keep in mind when designing this carbon as hydrogen adsorbent. These are:
1) The material must have a high gravimetric capacity for hydrogen measured in kg H2 per kg material.
2) The material must have a high volumetric capacity measured in liters of H2 per kg of material.
Please review the targets set by the U.S. Department of Energy for hydrogen storage materials. Here is the URL:
www.doe.gov
So far, activated carbon and MOF-5 have been considered for hydrogen storage. MOF-177 did not meet DOE targets.
Hope this helps answer your question.
Professor Yehia Khalil
Yale University
USA
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