The nanocrystalline and amorphous Mg2Ni-type electrode alloys with a composition of Mg20-xYxNi10(x=0, 1, 2, 3 and 4) were fabricated by mechanical milling. Effects of Y content on the structures and electrochemical hydrogen storage performances of the alloys were investigated in detail. The inspections of X-ray diffraction(XRD), transmission electron microscopy(TEM) and scanning electron microscopy(SEM) revealed that the substitution of Y for Mg brought on an obvious change in the phase composition of the alloys. The substitution of Y for Mg resulted in the formation of secondary YMgN i4 phases without altering the major phase Mg2 Ni when Y content x≤1. But with the further increase of Y content, the major phase of the alloys changed into YMgN i4 phase. In addition, such substitution facilitated the glass forming of the Mg2Ni-type alloy. The discharge capacities of the as-milled alloys had the maximum values with Y content varying, but Y content with which the alloy yielded the biggest discharge capacity was changeable with milling time varying. The substitution of Y for Mg had an insignificant effect on the activation ability of the alloys, but it dramatically improved the cycle stability of the as-milled alloys. The effect of Y content on the electrochemical kinetics of the alloys was related to milling time. When milling time was 10 h, the high rate discharge ability(HRD), diffusion coefficient of hydrogen atom(D) and charge transfer rate all had the maximum value with Y content increasing, but they always decreased in the same condition when milling time increased to 70 h.
Ce1-xBixO2-δ(x = 0.00, 0.03, 0.05, 0.07, 0.10, 0.15, 0.30) solid solutions were synthesized via a hydrothermal method. The structure, spectra and electrochemical transport properties of the samples were characterized systematically. The powder X-ray diffraction analysis showed that all of the doped samples exhibited single phase fluorite structure. The particle sizes decreased from 18 to 9 nm and the lattice parameters increased gradually with the dopant content increasing from x = 0.03 to x = 0.30. The Bi3+ doping also induced the F2 g Raman peak to shift from 463 to 455 cm-1, and caused a red shift of the band gap energies calculated from UV-Vis spectra. The impedance plots at different temperature demonstrated that the boundary resistance was much larger than the grain resistance, and two activation energy values were obtained in different temperature range.
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.
