Hydrogen storage materials for vehicular applications

Abstract

Hydrogen energy has been assessed as the clean and renewable energy source with the highest energy density. At present, 25% of energy demand comes from the transport sector, while 20% of greenhouse gases are produced from the transport sector at the global level. Hydrogen may be utilized in the vehicles as a fuel for fuel cell vehicles or as a hydrogen system in internal combustion engine vehicles. In both cases, hydrogen storage remains a key parameter. Various types of hydrogen storage materials have a wide range of operating conditions in terms of temperature, hydrogen plateau pressure, and hydrogen storage capacity with other relevant hydrogenation characteristics. At present, not a single hydrogen storage material is available to fulfill all the requirements of hydrogen storage for vehicles on the set target of DOE US. MgH2 has high hydrogen storage capacity equivalent to 7 wt%, but desorption temperature is 300°C. The normal vehicles do not operate at such a high temperature. Therefore, in the present communication, combinations of metal hydrides have been studied. The first combination belongs to MgH2 and AB2 system and another belongs to MgH2, NaAlH4, and AB2 system. In the calculation performed, it has been shown that the amount of heat and temperature available in the exhaust gas of a vehicle is enough to liberate the hydrogen from the high‐temperature metal hydride system. The calculated specific capacity on the system basis has been found as 1.13 kWh/kg (0.034 kgH2/kg) and 1.20 kWh/kg (0.036 kgH2/kg) for both combinations, respectively. These values of specific capacity are very much close to the present target of DOE US.