RESUMEN
The present study aimed to enhance the kinetics behavior and destabilize the thermal stability of MgH2 powder by high-energy milling of Mg powder under 50 bar of H2 for several hours using Ti-balls as the milling media. The results showed a monotonical increase in Ti content worn off the milling media and introduced into the milled powders. This gradual doping led to homogeneous distribution of fine Ti particles into the Mg/MgH2 powder matrix without agglomeration or compositional fluctuations at the micro-level. During the activation stage of the powders, achieved at 350 °C/35 bar H2 prior to hydrogenation kinetics measurements, elemental Ti reacted with H2 to form fine TiH2 particles. Our proposed in situ mechanically induced catalyzation approach was found to be mutually beneficial for decreasing the apparent activation energy of decomposition. In addition, introducing 5.3 wt% of TiH2 to the MgH2 powder obtained after 50 h led to the achievement of superior enhancement of gas uptake/release kinetics at relatively low temperatures. The nanocomposite MgH2/5.3 TiH2 powder possessed fast hydrogenation/dehydrogenation kinetics behaviors and revealed long cycle lifetimes. This system was successfully employed as a solid-state hydrogen source to charge the battery of a cell-phone device using an integrated Ti-tank/commercial proton exchange membrane-fuel cell system.
RESUMEN
Storing hydrogen gas into cylinders under high pressure of 350 bar is not safe and still needs many intensive studies dedic ated for tank's manufacturing. Liquid hydrogen faces also severe practical difficulties due to its very low density, leading to larger fuel tanks three times larger than traditional gasoline tank. Moreover, converting hydrogen gas into liquid phase is not an economic process since it consumes high energy needed to cool down the gas temperature to -252.8 °C. One practical solution is storing hydrogen gas in metal lattice such as Mg powder and its nanocomposites in the form of MgH2. There are two major issues should be solved first. One related to MgH2 in which its inherent poor hydrogenation/dehydrogenation kinetics and high thermal stability must be improved. Secondly, related to providing a safe tank. Here we have succeeded to prepare a new binary system of MgH2/5 wt. % TiMn2 nanocomposite powder that show excellent hydrogenation/dehydrogenation behavior at relatively low temperature (250 °C) with long cycle-life-time (1400 h). Moreover, a simple hydrogen storage tank filled with our synthetic nanocomposite powders was designed and tested in electrical charging a battery of a cell phone device at 180 °C through a commercial fuel cell.
RESUMEN
One practical solution for utilizing hydrogen in vehicles with proton-exchange fuel cells membranes is storing hydrogen in metal hydrides nanocrystalline powders. According to its high hydrogen capacity and low cost of production, magnesium hydride (MgH2) is a desired hydrogen storage system. Its slow hydrogenation/dehydrogenation kinetics and high thermal stability are the major barriers restricting its usage in real applications. Amongst the several methods used for enhancing the kinetics behaviors of MgH2 powders, mechanically milling the powders with one or more catalyst species has shown obvious advantages. Here we are proposing a new approach for gradual doping MgH2 powders with Ni particles upon ball milling the powders with Ni-balls milling media. This proposed is-situ method showed mutually beneficial for overcoming the agglomeration of catalysts and the formation of undesired Mg2NiH4 phase. Moreover, the decomposition temperature and the corresponding activation energy showed low values of 218 °C and 75 kJ/mol, respectively. The hydrogenation/dehydrogenation kinetics examined at 275 °C of the powders milled for 25 h took place within 2.5 min and 8 min, respectively. These powders containing 5.5 wt.% Ni performed 100-continuous cycle-life time of hydrogen charging/discharging at 275 °C within 56 h without failure or degradation.