The element Ni in the Mg_2Ni alloy is partially substituted by M(M = Cu, Co, Mn) in order to ameliorate the electrochemical hydrogen storage performances of Mg_2Ni-type electrode alloys. The nanocrystalline and amorphous Mg_(20)Ni_(10-x)M_x(M = None, Cu, Co, Mn; x = 0-4) alloys were prepared by melt spinning. The effects of the M(M = Cu, Co, Mn) content on the structures and electrochemical hydrogen storage characteristics of the as-cast and spun alloys were comparatively studied. The analyses by XRD, SEM and HRTEM reveal that all the as-cast alloys have a major phase of Mg_2Ni but the M(M = Co, Mn) substitution brings on the formation of some secondary phases, MgCo_2 and Mg for the(M = Co) alloy, and Mn Ni and Mg for the(M = Mn) alloy. Besides, the as-spun(M = None, Cu) alloys display an entirely nanocrystalline structure, whereas the as-spun(M = Co, Mn) alloys hold a nanocrystalline/amorphous structure, suggesting that the substitution of M(M = Co, Mn) for Ni facilitates the glass formation in the Mg_2Ni-type alloys. The electrochemical measurements indicate that the variation of M(M = Cu, Co, Mn) content engenders an obvious effect on the electrochemical performances of the as-cast and spun alloys. To be specific, the cyclic stabilities of the alloys augment monotonously with increasing M(M = Cu, Co, Mn) content, and the capacity retaining rate(S20) is in an order of(M = Cu) >(M = Co) >(M = Mn) >(M = None) for x≤1 but changes to(M = Co) >(M = Mn) >(M = Cu) >(M = None) for x≥2. The discharge capacities of the as-cast and spun alloys always grow with the rising of M(M = Co, Mn) content but first mount up and then go down with increasing M(M = Cu) content. Whatever the M content is, the discharge capacities are in sequence:(M = Co) >(M = Mn) >(M = Cu) >(M = None). The high rate discharge abilities(HRDs) of all the alloys grow clearly with rising M(M = Cu, Co) content except for(M = Mn) alloy, whose HRD has a maximum value with varying M(M = Mn) content. Furthermore, for the as-cast alloys, the HRD is in order
Melt spinning technology was used to prepare the Mg2Ni-type(Mg24Ni10Cu2)100–x Ndx(x=0,5,10,15,20)alloys in order to obtain a nanocrystalline and amorphous structure.The effects of Nd content and spinning rate on the structures and electrochemical hydrogen storage performances of the alloys were investigated.The structure characterizations of X-ray diffraction(XRD),transmission electron microscopy(TEM)and scanning electron microscopy(SEM)linked with energy dispersive spectroscopy(EDS)revealed that the as-spun Nd-free alloy displayed an entire nanocrystalline structure,whereas the as-spun Nd-added alloys held a nanocrystalline and amorphous structure and the degree of amorphization visibly increased with the rising of Nd content and spinning rate,suggesting that the addition of Nd facilitated the glass forming of the Mg2Ni-type alloy.The electrochemical measurements indicated that the addition of Nd and melt spinning improved the electrochemical hydrogen storage performances of the alloys significantly.The discharge capacities of the as-cast and spun alloys exhibited maximum values when Nd content was x=10,which were86.4,200.5,266.3,402.5 and 452.8 mAh/g corresponding to the spinning rate of 0(As-cast was defined as the spinning rate of 0 m/s),10,20,30 and 40 m/s,respectively.The cycle stability(S20,the capacity maintain rate at 20thcycle)of the as-cast alloy always rose with the increasing of Nd content,and those of the as-spun alloys exhibited the maximum values for Nd content x=10,which were77.9%,83.4%89.2%and 89.7%,corresponding to the spinning rate of 10,20,30 and 40 m/s,respectively.
The La–Mg–Ni-based A2B7-type La0.8Mg0.2Ni3.3Co0.2Six(x=0-0.2)electrode alloys were prepared by casting and annealing.The influences of the additional silicon and the annealing treatment on the structure and electrochemical performances of the alloys were investigated systemically.Both of the analyses of XRD and SEM reveal that the as-cast and annealed alloys are of a multiphase structure,involving two main phases(La,Mg)2Ni7 and LaNi5 as well as one minor phase LaNi3.The addition of Si and annealing treatment bring on an evident change in the phase abundances and cell parameters of(La,Mg)2Ni7 and LaNi5 phase for the alloy without altering its phase structure.The phase abundances decrease from 74.3%(x=0)to 57.8%(x=0.2)for the(La,Mg)2Ni7 phase,and those of LaNi5 phase increase from 20.2%(x=0)to 37.3%(x=0.2).As for the electrochemical measurements,adding Si and performing annealing treatment have engendered obvious impacts.The cycle stability of the alloys is improved dramatically,being enhanced from 80.3% to 93.7% for the as-annealed(950 °C)alloys with Si content increasing from 0 to 0.2.However,the discharge capacity is reduced by adding Si,from 399.4 to 345.3 mA·h/g as the Si content increases from 0 to 0.2.Furthermore,such addition makes the electrochemical kinetic properties of the alloy electrodes first increase and then decrease.Also,it is found that the overall electrochemical properties of the alloys first augment and then fall with the annealing temperature rising.
The nanocrystalline and amorphous Mg-Nd-Ni-Cu quaternary alloys with a composition of(Mg24Ni10Cu2)100-xNdx（x = 0-20） were prepared by melt spinning.The X-ray diffraction and transmission electron microscopy inspections reveal that,by varying the spinning rate and the Nd content,different microstructures could be obtained by melt spinning.Particularly,the as-spun Nd-free alloy holds an entire nanocrystalline structure but the as-spun Nd-added alloy has a nanocrystalline and amorphous structure,which implies that the addition of Nd facilitates the glass forming in the Mg2Ni-type alloy.Also,the degree of the amorphization in the as-spun Nd-added alloys clearly increases with increasing the spinning rate and the Nd content.The H-storage capacity and the hydrogenation kinetics of amorphous,partially and completely nanocrystalline alloys were investigated and it was found that they are dependent on the microstructure and the phase composition of the alloys.Specially,enhancing the spinning rate from 0（the as-cast was defined as the spinning rate of 0 m/s） to 40 m/s makes the hydrogen absorption saturation ratio（R5a）（a ratio of the hydrogen absorption quantity in 5 min to the saturated hydrogen absorption capacity） increase from 35.2%to90.3%and the hydrogen desorption ratio(R10d)（a ratio of the hydrogen desorption quantity in 10 min to the saturated hydrogen absorption capacity） rise from 12.7%to 44.9%for the（x = 5） alloy.And the growing of the Nd content from 0 to 20 gives rise to the R5a and R10d values rising from 85.7%to 94.5%and from36.7%to 54.8%for the as-spun（30 m/s） alloys,respectively.
