Characteristics of MOF, MWCNT and graphene containing materials for hydrogen storage: A review

Hydrogen is a generally abundant, safe, clean and environmentally apt alternative fuel, which replenishes the void generated by depleting fossil fuel reserves. The adoption of hydrogen as an energy source has been restricted to low levels due to the complications associated with its viable storage and usage. Existing technologies, such as storage of hydrogen in compressed and liquefied forms are not adequate to meet the broad on-board applications. The gravimetric energy density (120 MJ/kg) of hydrogen is three times higher than that of gasoline products, so solid-state hydrogen storage is advantageous. Metal-organic frameworks (MOFs), multi-walled carbon nanotubes (MWCNTs) and graphene are solid adsorbents majorly employed for efficient H2 storage. The prominent features of MOFs such as permanent porosity, structural rigidity, and surface area are attractive and ideal for hydrogen storage. In addition, nanostructured carbon materials (MWCNTs and graphene) and their composites have demonstrated significant hydrogen storage capacities. Some important parameters for the success of the hydrogen economy include high storage density, adsorption/desorption temperature and cycling time. Cryo-hydrogen storage was achieved in MOFs and their composites with carbon structures, but storage at ambient temperature and acceptable pressures is a major hurdle. This review discusses various strategies and mechanisms in the design of adsorbents explored to improve H2 storage capacities and afford opportunities to develop new sustainable hydrogen technologies to meet energy targets.