Gaseous and Electrochemical Hydrogen Storage Properties of Nanocrystalline Mg₂Ni-Type Alloys Prepared by Melt Spinning

A partial substitution of Ni by Cu has been carried out in order to improve the hydrogen storage characteristics of the Mg2Ni-type alloys. The nanocrystalline Mg20Ni10-xCux (x = 0, 1, 2, 3, 4) alloys are synthesized by the melt-spinning technique. The structures of the as-cast and spun alloys have been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM). The electrochemical performances were evaluated by an automatic galvanostatic system. The hydrogen absorption and desorption kinetics of the alloys were determined by using an automatically controlled Sieverts apparatus. The results indicate that the substitution of Cu for Ni does not alter the major phase Mg2Ni. The Cu substitution significantly ameliorates the electrochemical hydrogen storage performances of alloys, involving both the discharge capacity and the cycle stability. The hydrogen absorption capacity of alloys has been observed to be first increase and then decrease with an increase in the Cu contents. However, the hydrogen desorption capacity of the alloys exhibit a monotonous growth with an increase in the Cu contents.

Hydrogen Absorption and Electrochemical Properties of As-Quenched Nanocrystalline Mg20Ni10 – xCux (x = 0 – 4) Alloys

Nanocrystalline Mg2Ni-type alloys with nominal compositions of Mg20Ni10 – xCux (x = 0, 1, 2, 3, 4) were synthesized by rapid quenching technique. The microstructures of the as-cast and quenched alloys were characterized by XRD, SEM and HRTEM. The hydrogen absorption and desorption kinetics of the alloys were measured using an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system. The results show that all the as-quenched alloys hold a typical nanocrystalline structure, and the rapid quenching does not change the major phase Mg2Ni. The hydrogen absorption and desorption capacities of the alloys significantly increase with rising quenching rate. Additionally, the rapid quenching significantly improves the electrochemical hydrogen storage capacity of the alloys, but it slightly impairs the cycle stability of the alloys.

Gaseous hydrogen storage properties of Mg-Y-Ni-Cu alloys prepared by melt spinning

For purpose of promoting the hydrogen absorption and desorption thermodynamics and kinetics properties of Mg-Ni-based alloys, partially substituting Y and Cu for Mg and Ni respectively and melt spinning technique were applied for getting Mg25-xYxNi9 Cu(χ = 0-7) alloys. Their microstructures and phases were characterized with the help of X-ray diffraction and transmission electron microscopy. Their hydrogen absorbing and desorbing properties were tested by a Sievert apparatus, DSC, and TGA, which were connected with a H2 detector. In order to estimate the dehydrogenation activation energy of alloy hydride, both Arrhenius and Kissinger methods were applied for calculation. It is found that their hydriding kinetics notably declines, however, their hydrogen desorption kinetics conspicuously improves, with spinning rate and Y content increasing. Their hydrogen desorption activation energy markedly decreases under the same constraint, and it is found that melt spinning and Y substituting Mg improve the real driving force for dehydrogenation. As for the tendency of hydrogen absorption capacity,it presents an elevation firstly and soon after a decline with the rising of spinning rate, however, it always lowers with Y content growing. With Y content and spinning rate increasing, their thermodynamic parameters(△H and △S absolute values) visibly decrease, and the starting hydrogen desorption temperatures of alloy hydrides obviously lower.

Structure and hydrogen storage characteristics of as-spun Mg-Y-Ni-Cu alloys

Experimental alloys with compositions of Mg(25-x)YxNi9Cu(x=0,1,3,5,7)have been successfully prepared through melt spinning method.The phase compositions and microstructures were measured by X-Ray diffraction(XRD)and high-resolution transmission electron microscopy(HRTEM).The de-/hydrogenation properties were measured by utilizing Sievert apparatus,differential scanning calorimetry(DSC)and thermal gravimetric analyzer(TGA)connected with a H2 detector.The Arrhenius and Kissinger methods were adopted to calculate their dehydrogenation activation energies.The results show that hydrogen absorption kinetics of the alloys notably decline while their hydrogen desorption kinetics conspicuously improve with spinning rate increasing.The dehydrogenation activation energy markedly decreases with spinning rate increasing,which makes the hydrogen desorption kinetics improve.The thermodynamic parameters(H and S absolute values)clearly decrease with spinning rate increasing.The hydrogen absorption capacity exhibits different trends with spinning rate rising.Specifically,hydrogen absorption capacity increases at the beginning and declines later for Y1 alloy,but that of Y7 alloy always decreases with spinning rate growing.