Reversible hydrogen storage at reduced temperatures in the intermetallic compound Mg6(Ni,Pd)
A rapidly-solidified Mg-Ni-Pd alloy is shown to exhibit reversible hydrogen-storage of 5 mass % H near atmospheric pressure at a temperature of 473 K, nearly 100 K below temperatures typically required for Mg-based alloys. Additionally, a single plateau is observed in the pressure-composition isotherm where MgH2 and Mg2NiH4 form and decompose simultaneously during the absorption/desorption process. The increase in absorption plateau pressure to 100 kPa suggests a decrease in the enthalpy of reaction between the hydride and metallic phases by as much as 15 kJ/mol, or 20 %. The decrease arises because of the formation of a new equilibrium metallic phase, Mg6(Ni,Pd). The phase alters the thermodynamics of the hydriding reaction, allowing both MgH2 and Mg2NiH4 to form cooperatively in a single reaction. This method for reducing the enthalpy of the hydriding reaction is promising, and may prove useful in a variety of other metal-hydride hydrogen-storage systems.
International Journal of Hydrogen Energy
Mg-based alloy, hydrogen storage, metal hydride, nanocrystalline material, metallic glass