Hydrogen Adsorption in Carbon Materials

Recent reports of very high, reversible adsorption of molecular hydrogen in pure nanotubes, alkali-doped graphite, and pure and alkali-doped graphite nanofibers (GNFs) have aroused tremendous interest in the research community, stimulating much experimental work and many theoretical calculations worldwide. The U.S. Department of Energy (DOE) Hydrogen Plan has seta standard for this discussion by providing a commercially significant benchmark for the amount of reversible hydrogen adsorption. This benchmark requires a system-weight efficiency (the ratio of stored H2 weight to system weight) of 6.5-wt% hydrogen and a volumetric density of 63 kg H2/m. If the encouraging experimental reports (summarized in Table I) are reproducible, it may be possible to reach the goals of the DOE Hydrogen Plan. On the other hand, the community still awaits confirmation of these experimental results by workers in other laboratories. Of additional concern is the fact that theoretical calculations have been unable to identify adsorption mechanisms compatible with the requirements of the DOE Hydrogen Plan. An economical, safe, hydrogen-storage medium is a critically needed component of a hydrogen-fueled transportation system. Hydrogen storage in a carbon-based material offers further advantages associated with its low mass density. Furthermore, fuel cell technology involving the conversion of hydrogen into protons, or hydrogen and oxygen into electric current, is being vigorously researched for both transportation and small power-plant applications.