A new nanonickel catalyst for hydrogen storage in solid-state magnesium hydrides

摘要

Transmission electron microscopy was used to study the morphology and character of new nanometric-scale Ni (nano-Ni) powders produced by a chemical vapour deposition process by Vale Inco (Canada). The morphology of the nano-Ni powder is filamentary or aciniform, and the Ni crystallites contain a relatively low density of lattice defects, mainly twins. Oxygen and carbon impurities formed surface films. In contrast, a submicro-Ni powder contains less C and a much lower O concentration, resulting in significantly less surface film formation compared to the finer nano-Ni. Catalytic properties of these powders, as an additive to MgH_2 hydrogen storage media, have been investigated. When ball-milled with high-enthalpy hydrides, viz. MgH_2, the nano-Ni exhibits strong catalytic properties and lowers greatly the activation energy (E_A) by 50%, but does not affect the enthalpy. Consequently, the desorption temperature can be lowered by almost 100 ℃. It is anticipated that when ball-milled with low-enthalpy complex hydrides, this new nanonickel catalyst will have a paramount effect on destabilization of mostly kinetically stabilized hydride complexes. The peculiar C and oxide coatings may affect sintering during hydride discharging.