Desorption behaviour and microstructure change of nanostructured hydrided AZ31 Mg alloy powders

In order to optimize the dehydriding process for producing nanocrystalline Mg alloy powders by hydriding-dehydriding treatment,nano-structured as-hydrided Mg-3%Al-1%Zn(AZ31 Mg)(mass fraction)alloy powders were thermally dehydrided at various temperatures from 275 to 375℃.The kinetics of hydrogen desorption was examined by hydrogen discharge measurement during dehydriding.The microstructure of the as-hydrided and the subsequently fully dehydrided alloy powders was investigated by X-ray diffraction analysis(XRD)and transmission electron microscopy(TEM),respectively.Both the desorption kinetics and the grain size of the alloy after complete dehydriding were found to be strongly dependent on the processing temperature.The higher the temperature,the faster the desorption,and the more significant the grain growth.When the desorption temperature was raised from 300 to 375℃,the time to achieve complete dehydriding was shortened from 190 to 20 min,and the average grain size increased correspondingly from 20 to 58 nm.

Charge/Discharge Hysteresis Characteristics of an Amorphous Mg_(50)Ni_(50) Hydride Electrode

The hydrogenation/dehydrogenation thermodynamic properties of a Mg 50 Ni 50 alloy synthesized by mechanical alloying is measured by electrochemical method, and serious hydrogenation/dehydrogenation hysteresis characteristic was observed. The electrochemical impedance of the electrode discharge reaction of this electrode is mainly composed of charge transfer resistance R ct , hydrogen diffusion impedance Z w and surface H adsorption/desorption capacitance C ads . Electrochemical impedance analysis reveals that R ct is about one degree larger than the other impedance component. Thus it is reasonable to believe that discharge reaction is mainly dominated by the charge transfer reaction at the alloy surface, and the discharge hysteresis phenomenon is related to the factors that effect the charge transfer reaction. Hydroxides are present in the alloy surface before and after charging/discharging. These hydroxides would decrease the conductivity of the alloy surface and hinder the charge transfer process.

Strategies to enhance hydrogen storage performances in bulk Mg-based hydrides

Bulk Mg-based hydrogen storage materials have the potential to provide a low-cost solution to diversify energy storage and transportation.Compared to nano powders which require handling and processing under hydrogen or an inert gas atmosphere,bulk Mg-based alloys are safer and are more oxidation re-sistant.Conventional methods and existing infrastructures can be used to process and handle these ma-terials.However,bulk Mg alloys have smaller specific surface areas,resulting in slower hydrogen sorp-tion kinetics,higher equilibrium temperatures,and enthalpies of hydride formation.This work reviews the effects of the additions of a list of alloying elements and the use of innovative processing meth-ods,e.g.,rapid solidification and severe plastic deformation processes,to overcome these drawbacks.The challenges,advantages,and weaknesses of each method and future perspectives for the development of Mg-based hydrogen storage materials are discussed.

Synergy between metallic components of MoNi alloy for catalyzing highly efficient hydrogen storage of MgH2

Catalysts play a critical role in improving the hydrogen storage kinetics in Mg/MgH2 system.Exploring highly efficient catalysts and catalyst design principles are hot topics but challenging.The catalytic activity of metallic elements on dehydrogenation kinetics generally follows a sequence of Ti>Nb>Ni>V>Co>Mo.Herein,we report a highly efficient alloy catalyst composed of low-active elements of Mo and Ni(i.e.MoNi alloy)for MgH2 particles.MoNi alloy nanoparticles show excellent catalytic effect,even outperforming most advanced Ti-based catalysts.The synergy between Mo and Ni elements can promote the break of Mg-H bonds and the dissociation of hydrogen molecules,thus significantly improves the kinetics of Mg/MgH2 system.The MoNi-catalyzed Mg/MgH2 system can absorb and release 6.7 wt.%hydrogen within 60 s and 10 min at 300℃,respectively,and exhibits excellent cycling stability and low-temperature hydrogen storage performance.This study provides a strategy for designing efficient catalysts for hydrogen storage materials using the synergy of metal elements.