Phase structure and hydrogen storage properties of LaMg3.93Ni0.21 alloy

The phase structure and hydrogen storage property of LaMg3.93Ni0.21 alloy were studied.XRD and SEM results exhibited that LaMg3.93Ni0.21 alloy consisted mainly of LaMg3,La2Mg17 and LaMg2Ni phases;after hydriding/dehydriding process,all the three phases transformed,La3H7 phase existed and the actual hydrogen absorption phases were Mg and Mg2Ni phases.Pressure-composition-temperature (P-C-T)measurement showed that the reversible hydrogen storage capacity of LaMg3.93Ni0.21 alloy was 2.63 wt.%,and the absorption time for reaching 90%of the storage capacity was 124 s at 523 K,and it was 1850 s for deabsorbing 90%of the maximum dehydrogen capacity.The hydriding process of LaMg3.93Ni0.21 alloy followed the nucleation and growth mechanisms.The enthalpy and entropy for hydriding and dehydriding reactions of the Mg phase in LaMg3.93Ni0.21 alloy were calculated to be-66.38±1.10 kJ/mol H2,-100.96±1.96 J/(K·mol)H2 and 68.50±3.87 kJ/mol H2,98.28±5.48 J/(K·mol)H2,respectively.A comparison of these data with those of MgH2(-74.50 kJ/mol H2,-132.30 J/K·mol H2)suggested that the hydride of LaMg3.93Ni0.21 alloy was less stable than MgH2.The existence of La hydride and synergetic effect of multiphase led to higher reversible hydrogen storage capacity and better kinetic property at lower temperature for LaMg3.93Ni0.21 alloy.     

Phase structure and hydrogen storage properties of REMg8.35Ni2.18Al0.21 （RE=La, Ce, Pr, and Nd） hydrogen storage alloys

REMg 8.35Ni2.18Al0.21 (RE=La, Ce, Pr, and Nd) alloys were prepared by induction melting and following annealing. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that the alloys were composed of Mg2Ni, (La, Pr, Nd)Mg2Ni, (La, Ce)2Mg17 , (Ce, Pr, Nd)Mg12 and Ce2Ni7 phases. The above phases were disproportioned into Mg2NiH4 , MgH2 and REH x (x=2.51 or 3) phases in hydriding. CeH2.51 phase transformed into CeH2.29 phase in dehydriding, whereas LaH3 , PrH3 and NdH3 phases remained unchanged. The PrMg8.41Ni2.14Al0.20 alloy had the fastest hydriding kinetics and the highest dehydriding plateau pressure while the CeMg8.35Ni2.18Al0.21 alloy presented the best hydriding/dehydriding reversibility. The onset hydrogen desorption temperature of the CeMg8.35Ni2.18Al0.21 hydride decreased remarkably owing to the phase transformation between the CeH2.51 and the CeH2.29 .     

Effects of Fe-substitution for cobalt on electrochemical properties of La-Mg-Ni-based alloys

In order to improve electrochemical properties,especially cycling stability,Co was partially substituted by Fe in A2B7-type La-Mg-Ni-based alloys.The La0.74Mg0.26Ni2.55Co0.65-xFex(x=0,0.10,0.20,0.30) alloys were prepared by inductive melting,and their phase structure and electrochemical properties were studied.The XRD and SEM results showed that the alloys consisted mainly of(La,Mg)2Ni7 phase,(La,Mg)5Ni19 phase and LaNi5 phase,except for absence of LaNi5 phase in the non-substituted alloy.The(La,Mg)5Ni19 ph...     

化学镀覆聚吡咯对LaNi_(3.81)Mn_(0.30)Co_(0.79)Al_(0.10)储氢合金电化学动力学性能的影响

采用化学镀的方法在AB5型储氢合金La Ni3.81Mn0.30Co0.79Al0.10表面镀覆聚吡咯来改善合金电极的电化学性能。测试了镀覆后合金的微观形貌和其在不同镀覆温度(T=293 K,323 K,343 K)和不同镀覆时间(t=5 min,8 min,10 min)下的电化学性能。XRD分析表明,表面镀覆聚吡咯没有改变合金的晶体结构,仍为La Ni5相;SEM-EDS和红外吸收光谱测试表明,经过表面处理之后合金表面附着了聚吡咯(PPy)导电高分子层。电化学测试表明,在不同处理温度下,当放电电流密度为323.53 m A/g时,合金电极的HRD从79.56%(T=293 K)增加到91.3%(T=323 K)。不同处理时间下,当放电电流密度为485.29 m A/g时,合金电极的HRD从70.4%(未处理)增加到80.3%(t=5 min)再增加到87.2%(t=8 min)。合金电极电化学动力学性能的显著改善是由于合金电极所镀覆的聚吡咯具有良好的导电性以及镀层抑制了合金电极在碱液中的腐蚀的原因。     

Phase Structure and Electrochemical Characteristics of Ml（Ni3.55Co0.75Mn0.40Al0.30）5x （x=0.88, 0.92, 0.96, 1.00） Hydrogen Storage Alloys

The phase structure and electrochemical characteristics of Ml （（Ni3.55Co0.75Mn0.40Al0.30）sx （ x = 0.88, 0.92, 0.96, 1.00） hydrogen storage alloys were studied. The effect of the stoichiometric ratio on the phase structure and electrochemical characteristics was analyzed. The results of XRD reveal that all the alloys consist mainly of LaNi5 phase with the hexagonal CaCu5 structure. But a few of the diffraction peaks of La2Ni7 phase on XRD pattern are observed when x ≤ 0.92, and with decreasing x, the intensity of La2Ni7 diffraction peaks increases and the values of lattice parameters a and cell volume increase, c and c/a of LaNi5 phase decrease gradually. When x≥0.96, La2Ni7 phase disappears and the alloys become single CaCu5-type. The electrochemical tests show that the maximum discharge capacity, high rate dischargeability and low temperature dischargeability are improved to different degrees by adjusting the stoichiometric ratio.