Abstract
Magnesium hydride (MgH2) holds immense promises as a cost-effective hydrogen storage material that shows excellent storage capacity suitable for fuel cell applications. Due to its slow hydrogen charging/discharging kinetics and high apparent activation energy of decomposition, MgH2 is usually doped with one or more catalytic agents to improve its storage capacity. So often, milling the metal hydride with proper amounts of catalyst leads to heterogeneous distribution of the catalytic agent(s) in MgH2 matrix. The present work proposes a cost-effective process for doping Mg powders with Zr2Ni particles upon ball milling the powders with Zr2Ni-balls milling media under pressurized hydrogen. Fine Zr2Ni particles were gradually eroded from the balls and homogeneously embedded into the milled powders upon increasing the ball milling time. As a result, these fine hard intermetallic particles acted as micro-milling media and leading to the reduction the Mg/MgH2 powders. Meanwhile, Zr2Ni eroded particles possessed excellent heterogeneous catalytic effect for improving the hydrogenation/dehydrogenation kinetics of MgH2. This is implied by the short time required to absorb (425 s)/desorb (700 s) 6.2 wt% H2 at 200 °C and 225 °C, respectively. The as-milled MgH2 with Zr2Ni balls possessed excellent cyclability, indexed by achieving continuous 646 cycles in 985.5 h (~1.5 cycle per hour) without serious degradation.
Highlights
Hydrogen storage nanocrystalline and nanocomposite materials are current area of tremendous research interest in chemistry, energy, materials science and the environment
The fabricated Zr2 Ni master alloys had nearly spherical-like shape ~10 mm in diameter (Figure 1c). These spherical-balls were used as milling media (MM) for conducting Reactive ball milling (RBM) of Mg powders under pressurized (50 bar) H2 (Figure 1d)
The results indicated that the system kept its constant value of storage range between ~980.5 h to 985.5 h
Summary
Hydrogen storage nanocrystalline and nanocomposite materials are current area of tremendous research interest in chemistry, energy, materials science and the environment. RBM has been intensively used to produce large amounts of high quality MgH2 nanocrystalline powders, starting from Mg metal and hydrogen gas [3,4,5]. In contrast to the many attractive properties found in MgH2 material, it is seldomly used in desired fuel cell application without intensive treatment [6,7,8,9,10]. This is attributed to high activation energy, high decomposition temperature and slow absorption/desorption kinetics [11,12,13,14]. Apart from the mechanical treatment approach, catalyzation MgH2 powders with proper volume fractions of catalytic agents [21], including pure
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