In this work, we have shown that the hydrogen gravimetric storage capacity of activated carbons depends strongly on their pore size distribution. Pores of different sizes 'collect' different amounts of hydrogen and hence do not contribute equally to the carbon storage capacity. It follows that the total pore volume and surface area are not sufficient to describe that capacity. Calculations of the amount adsorbed in the pores of different sizes show that H2 density drops very quickly with increasing pore size. 'Good' pores that adsorb H2 at high density are those that are smaller than 10-15 Ä. Pores larger than 20 Ä do not contribute much to the storage capacity and may be considered underused. The volumetric storage capacity depends on the gravimetric storage capacity and on the material packing density. Large volume of wider pores is detrimental to the volumetric capacity in two ways: (i) these pores do not adsorb H2 effectively; (ii) they contribute to the volume of carbon material and thus reduce its density. A carbon having the lowest gravimetric storage capacity (e.g. CS sample) may have the highest volumetric capacity if it contains only 'good' pores that adsorb H2 at high density. Carbon materials with high pore volume of pores smaller than 10-15 Ä are the best candidates to reach the high targets of storage capacity.
Optimizing H2 volumetric storage capacity of carbon materials for mobile applications
Optimierung der Wasserstoffvolumenspeicherungskapazität von Kohlenstoffwerkstoffen für mobile Anwendungen
2009
8 Seiten, 3 Bilder, 2 Tabellen, 22 Quellen
Conference paper
English
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