LaNi5 Phase Research Articles

Phase transformations and phase equilibria in the La–Ni and La–Ni–Fe systems. Part 1: Liquidus & solidus projections

Phase equilibria in the La–Ni and La–Ni–Fe systems were studied using DTA, X-ray diffraction, SEM and EPMA. La–Ni phase diagram, liquidus and solidus projections, melting diagram and a Scheil reaction scheme for the La–Ni–Fe system over the whole concentration range were constructed. Among binary compounds LaNi5, La5Ni19 and La2Ni7 have large homogeneity ranges and dissolve at the solidus temperature up to 21.9, 16.1 and 14.0 at.% Fe, respectively. The homogeneity ranges of the remaining phases are smaller. No ternary compounds have been identified in the La–Ni–Fe system. Liquidus projection is characterized by 13 fields of primary solidification of the component-based solid solutions (γFe,Ni), (δFe), (αFe), (βLa), (γLa) and solid solutions based on binary phases LaNi5, La5Ni19, La2Ni7, LaNi3, La7Ni16, La2Ni3, LaNi, La7Ni3 and La3Ni. The solidus projection is characterized by ten three-phase fields, which result from invariant four-phase equilibria, three are of eutectic type and seven of transition type.

Influence of the synthesis route on hydrogen sorption properties of La2MgNi7Co2 alloy

Solid-gas and electrochemical hydrogenation properties of La2MgNi7Co2 alloy are presented. Hydrogen concentration of 1.90 wt% at hydrogen pressure of 10 bar has been reached. The influence of the fabrication technology of La2MgNi7Co2 alloy on electrochemical performance of the hydride electrode were studied and discussed. To evaluate electrochemical characteristics of La2MgNi7Co2 electrodes including discharge capacity, self-discharge and kinetic parameters the galvanostatic charge/discharge technique was used. The studied samples were a multiphase. The presence of Mg-enriched phases (La2MgOx, (La, Mg)Ni3 and LaMgNi4) raises hydrogen capacity and makes an electrode less susceptible for the self-discharge effect. On the other hand Mg-presence in MH electrodes lowers the hydrogen desorption rate. It was found that, the dominant abundance of the LaNi5 phase in the tested materials has a positive effect on the kinetic parameters of the hydride electrode.

Influence of melt spinning and annealing treatment on structures and hydrogen storage thermodynamic properties of La0.8Pr0.2MgNi3.6Co0.4 alloy

La0.8Pr0.2MgNi3.6Co0.4 alloys were prepared by induction melting, annealing and melt spinning techniques. The influences of annealing treatment and melt spinning on phase structure and hydrogen storage properties were systematically investigated. The results of X-ray diffraction determine that the as-cast and as-spun La0.8Pr0.2MgNi3.6Co0.4 alloys consist of LaMgNi4 and LaNi5 phases, while only LaMgNi4 phase is present in the as-annealed alloy. The scanning electron microscope images illustrate that the grain of the alloy is significantly refined by melt spinning technology. The gaseous hydrogen storage kinetic and thermodynamic properties were measured by using a Sievert’s apparatus at different temperatures. The maximum hydrogen storage capacity of the as-cast, as-spun and as-annealed La0.8Pr0.2MgNi3.6Co0.4 alloy is 1.699, 1.637 and 1.535 wt.% at 373 K and 3 MPa, respectively. The annealed alloy has flatter and wider pressure plateaus compared with the as-cast and as-spun alloys, which correspond to the hydrogen absorption and desorption process of LaMgNi4 and corresponding hydride. Furthermore, the enthalpy and entropy changes of LaMgNi4 during hydrogenation at different temperatures were calculated using Van’t Hoff methods.

A Novel Synthesis Method of La–Mg‐Ni‐based Superlattice by LaNi5 Absorbing Gas‐state Mg

AbstractLa−Mg‐Ni based alloys are considered as future negative material for Ni‐MH batteries, while the volatilization of Mg hinders their application. Mg volatilization is considered irreversible in the preparation process. Herein, we provide a novel process to produce superlattice La−Mg‐Ni‐based alloy via alloying gas‐state Mg with LaNi5 slice. The formation of superlattice structures is verified in detail by microstructure characterization and element distribution analysis. The results indicate that there exists an equilibrium state for Mg solution in the La−Mg‐Ni alloy, and the gas‐state Mg atoms are directly absorbed by the LaNi5 alloy. With increasing the absorption time, Mg in LaNi5 slice bends to become more homogenous. It is attributed that the integration of the gas‐state Mg atoms leads to the transformation of the crystal structure of the LaNi5 cells on the slice surface into MgCu4Sn‐type phase, thus the solid LaNi5 phase turn to liquid MgCu4Sn‐type phase under the high temperature. Further, the liquid phase permeates into the inside of the LaNi5 slice along crystal boundaries which alloys with LaNi5 lattices to form Ce2Ni7‐type phase. This technology proves that the migration of metal atoms in gas state can induce a regroup phenomenon to form solid state crystal and provides a brand method for hydrogen storage materials preparation.

Stability of LaNi5-xCox alloys cycled in hydrogen — Part 1 evolution in gaseous hydrogen storage performance

In this study, the evolution trends in various hydrogen storage properties as well as kinetics performance of LaNi5−xCox (x = 0, 0.25, 0.50 and 0.75) alloys up to 1000 cycles are studied, and the effects of Co on the long-term hydrogen absorption/desorption properties are revealed. The alloys have single LaNi5 phase structure. The cell volume increases with increasing Co content, resulting in a lower hydrogen absorption/desorption plateau pressure and a more stable hydride phase. The alloys have good kinetics performance and can fully absorb hydrogen within 300 s. The hydrogen absorption rate increases with either cycling or Co addition, but neither of them changes the rate limiting step which remains to be diffusion controlled model in the temperature range of 343–383 K. With cycling, an intermediate γ phase emerges with the coexistence of α and β phases indicated by an extra higher plateau in P-C-T curves. This γ phase acts as a buffer releasing the microstrains which is reflected from the slower capacity degradation, and the significant decrease in hysteresis and slope factor upon its appearance. Moreover, the c/a value increases after 1000 cycles which also relieves the microstrains in the alloys. Co addition not only enhances the buffer effect of γ phase by partially combining it with β phase, but also promotes the increasing degree of c/a value, contributing to a better crystal structure, bigger particle size and higher cycle stability during long-term cycling.

Effect of melt spinning on the structural and low temperature electrochemical characteristics of La-Mg-Ni based La0.65Ce0.1Mg0.25Ni3Co0.5 hydrogen storage alloy

The influence of melt spinning on the structural and electrochemical performances of A2B7-type La0.65Ce0.1Mg0.25Ni3Co0.5 alloy electrodes at 298, 268, 258 and 248 K is investigated. The Rietveld refinement result reveals that the melt-spun alloys are mainly composed of (La, Mg)Ni3, (La, Mg)2Ni7 and LaNi5 phase, as the spinning rate is enhanced from 0 (the as-cast is defined as the spinning rate of 0 m s−1) to 30 m s−1, the abundance of LaNi5 phase increases while that of (La, Mg)Ni3 and (La, Mg)2Ni7 phase shares a reverse trend. The electrochemical measurement indicates that the cyclic stability of 100 charge/discharge cycles of the La0.65Ce0.1Mg0.25Ni3Co0.5 alloy increases with the rising of spinning rate. When the spinning rate is 10 m s−1, the discharge capacity of the 100th cycle for the La0.65Ce0.1Mg0.25Ni3Co0.5 alloy reaches the maximum value ranging from 245.9 to 268.3 mAh g−1 within the test temperature ranging from 248 to 298 K, and the high rate discharge ability of the alloy also reaches the optimum value. Thus the La0.65Ce0.1Mg0.25Ni3Co0.5 alloy exhibits optimum electrochemical properties when the spinning rate is 10 m s−1.

Structure and hydrogen storage properties of AB3-type Re2Mg(Ni0.7\u2009\u2212\u2009xCo0.2Mn0.1Alx)9 (x\u2009=\u20090\u20120.04) alloys

Re2Mg(Ni0.7 − xCo0.2Mn0.1Alx)9 (x = 0‒0.04) alloys are prepared by induction melting, and the influence of the partial substitution of Ni by Al on the structure, hydrogen storage, and electrochemical properties of the alloys are investigated systematically. These alloys mainly consist of two main phases with LaNi5 phase and (La,Mg)2Ni7 phase, and minor LaNi2 phase. The pressure-composition isotherms shows that, with Al content increasing in the alloys, the maximum hydrogen storage capacity decreased from 1.16 wt% (x = 0) to 0.99 wt% (x = 0.04). The changes of enthalpy and entropy reveal that the thermodynamic stability and the disordered degree of the hydride alloys increase with the Al addition. Results of electrochemical studies indicate that the substitution of Al for Ni can noticeably improve the cycle stability of the alloy electrode. The capacity retention after 80 cycles is enhanced from 63.6% (x = 0) to 76.5% (x = 0.04). However, the maximum discharge capacity of the alloys decreases. The Re2Mg(Ni0.7 − xCo0.2Mn0.1Alx)9 (x = 0‒0.04) alloys exhibit excellent dischargeability.

Enhanced cycling stability and high rate dischargeability of A2B7-type La–Mg–Ni-based alloys by in-situ formed (La,Mg)5Ni19 superlattice phase

In this work, various amounts of (La,Mg)5Ni19 phase is successfully produced in a A2B7-type La0.75Mg0.25Ni3.5 alloy by zone heating the as-cast alloy at the peritectic reaction temperature of the (La,Mg)5Ni19 phase (1203 K) for different durations. The formation process, electrochemical effects and functioning mechanism of the (La,Mg)5Ni19 phase are studied. The as-cast alloy contains (La,Mg)2Ni7 and LaNi5 main phases, and (La,Mg)5Ni19 minor phase. During zone heating, the peritectic reaction between the LaNi5 solid phase and the melted (La,Mg)2Ni7 liquid phase occurs, forming (La,Mg)5Ni19 phase. Thus the (La,Mg)5Ni19 phase abundance increases from 9.8 wt% (as-cast) to 46.2 wt% (heated for 24 h). The hydrogen desorption plateau pressure of the alloys increases with increasing (La,Mg)5Ni19 phase abundance, contributing to fast hydrogen desorption and large current dischargeability. In addition, the (La,Mg)5Ni19 phase network in the alloy matrix has a good structural stability against repeated hydrogen absorption/desorption, keeping the alloy from serious lattice destruction and crystal defects. Moreover, the discrete expansion/contraction between the LaNi5 phase and the superlattice phases during cycling decreases with the consumption of the LaNi5 phase, which relives the alloys' pulverization, and thus enhancing the oxidation resistance. Thereby, the cycling stability of the alloy electrodes of the 150th cycle increases from 65.4% (9.8 wt% (La,Mg)5Ni19 phase) to 80.4% (46.2 wt% (La,Mg)5Ni19 phase).

Electrochemical hydrogen storage behaviors of as-cast and spun RE–Mg–Ni–Co–Al-based AB2-type alloys applied to Ni–MH battery

Preparation of La–Mg–Ni–Co–Al-based AB2-type alloys La0.8−xCe0.2YxMgNi3.4Co0.4Al0.1 (x = 0, 0.05, 0.10, 0.15, 0.20) was performed using melt spinning technology. The influences of spun rate and Y content on structures and electrochemical hydrogen storage characteristics were studied. The base phase LaMgNi4 and the lesser phase LaNi5 were detected by X-ray diffraction (XRD) and scanning electron microscope (SEM). The variations of spinning rate and Y content cause an obvious change in phase content, but without altering phase composition, namely, with spinning rate and Y content growing, LaMgNi4 phase content augments while LaNi5 content declines. Furthermore, melt spinning and the replacing La by Y refine the grains dramatically. The electrochemical tests show a favorable activation capability of the two kinds of alloys, and the maximum discharge capacities are achieved during the first cycle. Discharge capacity firstly increases and subsequently decreases with spinning rate rising, while cycle stability is ameliorated and discharge capacity decreases with Y addition increasing. It is found that the amelioration of cycle stability is due to the enhancement of anti-pulverization, anti-corrosion and anti-oxidation abilities by both replacement of La with Y and melt spinning. Moreover, with the increase of Y addition and/or spinning rate, the electrochemical kinetics that contain charge transfer rate, limiting current density (IL), hydrogen diffusion coefficient (D) and the high rate discharge ability (HRD) firstly augment and then reduce.

Structures and Electrochemical Performances of As-spun RE-Mg-Ni-Mn-based Alloys Applied to Ni-MH Battery

The La-Mg-Ni-Mn-based AB2-type La1-xCexMgNi3.5Mn0.5 (x = 0, 0.1, 0.2, 0.3, and 0.4) alloys were fabricated by melt spinning technology. The effects of Ce content on the structures and electrochemical hydrogen storage performances of the alloys were studied systematically. The XRD and SEM analyses proved that the experimental alloys consist of a major phase LaMgNi4 and a secondary phase LaNi5. The variation of Ce content causes an obvious change in the phase abundance of the alloys without changing the phase composition. Namely, with the increase of Ce content, the LaMgNi4 phase augments and the LaNi5 phase declines. The lattice constants and cell volumes of the alloys clearly shrink with increasing Ce content. Moreover, the Ce substitution for La results in the grains of the alloys clearly refined. The electrochemical tests showed that the substitution of Ce for La obviously improves the cycle stability of the as-spun alloys. The analyses on the capacity degradation mechanism demonstrate that the improvement can be attributed to the ameliorated anti-corrosion and anti-oxidation ability originating from substituting partial La with Ce. The as-spun alloys exhibit excellent activation capability, reaching the maximum discharge capacities just at the first cycling without any activation treatment. The substitution of Ce for La evidently improves the discharge potential characteristics of the as-spun alloys. The discharge capacity of the alloys first increases and then decreases with growing Ce content. Furthermore, a similar trend also exists in the electrochemical kinetics of the alloys, including the high rate discharge ability (HRD), hydrogen diffusion coefficient (D), limiting current density (IL) and charge transfer rate.

Structure and Electrochemical Properties of Ball‐Milled La15Fe2Ni72Mn7B2Al2 Hydrogen Storage Alloys with Graphene

AbstractIn order to improve the electrochemical properties of the La‐Fe−B system hydrogen storage alloy, graphene was synthesized and added into the hydrogen storage alloy La15Fe2Ni72Mn7B2Al2. The La15Fe2Ni72Mn7B2Al2 alloy was prepared by arc‐melting and the La15Fe2Ni72Mn7B2Al2+ x wt. % graphene (x=1, 3, 5) composites were obtained by mechanical ball‐milling method. The effects of graphene addition on their electrochemical properties and dynamic performances have been discussed. Structure analyses showed that the La15Fe2Ni72Mn7B2Al2 alloy was composed of LaNi5 phase, La3Ni13B2 phase and (Fe, Ni) phase. The electrochemical experimental results demonstrate that the discharge capacity of ball‐milled La15Fe2Ni72Mn7B2Al2 hydrogen storage alloys with graphene was significantly improved. With 3 wt. % graphene addition, the maximum discharge capacity can reach 288.4 mAh⋅g−1, which is much higher than that of norm alloy (215.3 mAh⋅g−1). Moreover, the high‐rate dischargeability (HRD) and self‐discharge characteristics were also increased with graphene addition.

Electrochemical hydrogen storage performance of as-cast and as-spun RE-Mg-Ni-Co-Al-based alloys applied to Ni/MH battery

Abstract The La-Mg-Ni-Co-Al-based AB2-type La0.8–xCe0.2YxMgNi3.4Co0.4Al0.1 (x=0, 0.05, 0.1, 0.15, 0.2) alloys were prepared via melt spinning. The analyses of the X-ray diffraction (XRD) and scanning electron microscopy (SEM) proved that the experimental alloys contain the main phase LaMgNi4 and the second phase LaNi5. Increasing Y content and spinning rate lead to grain refinement and obvious change of the phase abundance without changing phase composition. Y substitution for La and melt spinning make the life-span of the alloys improved remarkably, which is attributed to the improvement of anti-oxidation, anti-pulverization and anti-corrosion abilities. In addition, the discharge capacity visibly decreases with increasing the Y content, while it firstly increases and then decreases with increasing spinning rate. The electrochemical kinetics increases to the optimum performance and then reduces with increasing spinning rate. Moreover, all the alloys achieve to the highest discharge capacities just at the initial cycle without activation.

Effects of Magnesium Content on Structure and Electrochemical Properties of La‐Mg‐Pr‐Al‐Mn‐Co‐Ni Hydrogen Storage Alloys

The discharge capacity, microstructures, and corrosion resistance of some as‐cast alloys represented by the formula La0.7−xMgxPr0.3Al0.3Mn0.4Co0.5Ni3.8, where x = 0.0, 0.1, 0.3, 0.5, and 0.7, were investigated by SEM/EDX, XRD, and electrochemical measurements. The partial substitution of La by Mg refined the grain structure while the total substitution changed it from equiaxed to columnar. Three phases were detected: a major phase (M), a grey phase (G), and a dark phase (D). The compositions analyzed by EDX suggested that the M phase was close to a LaNi5 phase. With the increase of the Mg content, the analyses revealed a G phase with composition close to a RMg2Ni9 (R = La,Pr) and a D phase close to a MgNi2 phase. The XRD analysis and Rietveld refinement corroborated the EDX results. The corrosion resistance of the alloys was evaluated in 6.0 mol·L−1 KOH solution, and the results showed that the substitution of La by Mg was beneficial for this alloy property. Nevertheless, Mg addition was deleterious to the discharge capacity of the electrodes.

Investigation of the structure, phase composition, and electrochemical characteristics of hydrogen-sorbing intermetallics of the La–Mg–Ni system obtained by the sintering method

The crystal structure, phase composition, and electrochemical properties of the materials obtained by sintering of (LaNi3+Mg+Ni) powder mixture in the temperature range 640–1020°С have been investigated. Experimental results show that, at temperatures of ≤850°С, the sintered multiphase material, whose major phases are phases with PuNi3-type structure (LaMg2Ni9 and LaNi3) and CaCu5-type structure (LaNi5), is formed. With increase in temperature, the number of phases in the sintered material decreases to a single major phase LaNi5, and the content of the LaMg2Ni9 phase practically does not change. It has been established that increase in sintering temperature deteriorates the activation of the electrode materials and slows down the hydrogen absorption process. At the same time, the maximum discharge capacity and cyclic stability of electrodes increase.

Microstructures and hydrogen storage properties of La[sbnd]Ni[sbnd]Fe[sbnd]V[sbnd]Mn alloys

Multicomponent high entropy alloys based on LaNi5 phase are investigated as hydrogen storage materials. The multicomponent LaNiFeVMn alloys are produced from pre-alloyed and elemental gas-atomized powders using Laser Engineered Net Shaping (LENS) technology. The effect of the alloy chemical composition on the hydrogen storage properties are elucidated in terms of the structure, phase composition and alloy formation entropies. The results of phase analysis indicates that laser manufactured alloys possess primary two-phase structure that changes from σ + La(Ni,Mn)5 to FCC + La(Ni,Mn)5 alloys. Maximum hydrogen capacity of LaNiFeVMn alloys is proportional to the atomic content of lanthanum which is able to form CaCu5-type La(Ni,Mn)5 phase. Produced alloys show differential behavior while forming the hydride phase and no simple relationship between phase compositions and pressure-composition curves can be observed.

Influence of the substitution Ce for La on structural and electrochemical characteristics of La0.75-xCexMg0.25Ni3Co0.5 (x=0, 0.05, 0.1, 0.15, 0.2 at. %) hydrogen storage alloys

Structural and electrochemical performances of La0.75-xCexMg0.25Ni3Co0.5 (x = 0, 0.05, 0.1, 0.15, 0.2 at.%) alloys prepared by an induction melting under helium atmosphere followed by annealing treatment at 1173 K in a vacuum furnace for 8 h are studied. Rietveld refinement results from the XRD data suggest that the alloys are mainly composed of (La, Mg)Ni3, (La, Mg)2Ni7 and LaNi5 phases. Increasing the content of Ce, the amounts of (La, Mg)Ni3 phase and (La, Mg)2Ni7 phase decrease, while the amount of LaNi5 phase increases. Electrochemical performance measurement results show that the La0.75-xCexMg0.25Ni3Co0.5 alloys are completely activated within 2 cycles, and the cyclic stability after 100 charge/discharge cycles of the alloys increases from 62.39% to 84.94% with the rising of Ce content, and the discharge capacity of the 100th cycle reaches the maximum value of 259 mAh/g when Ce content is 0.1 at.%. Meanwhile, the high rate discharge ability of the alloy electrodes increases to the maximum value when Ce content is 0.1 at.%, and then decreases. Thus, the La0.65Ce0.1Mg0.25Ni3Co0.5 alloy exhibits optimum comprehensive electrochemical properties.

Phase structure and electrochemical hydrogen storage performance of La4MgNi18M (M = Ni, Al, Cu and Co) alloys

The substitution of transition metals such as Ni is one of the effective methods to improve the electrochemical performance of La-Mg-Ni alloys because this considerably affects the chemical composition and phase structure of the alloys. In this study, A5B19-type hydrogen storage alloys with the elemental composition of La4MgNi18M (M = Ni, Al, Cu, and Co) were prepared by vacuum induction melting followed by annealing. In addition, the effect of the incorporation of M on the phase transformation and electrochemical performance was investigated. The X-ray diffraction profiles revealed the presence of AB5, A2B7 (Ce2Ni7 and Gd2Co7), and A5B19 (Pr5Co19 and Ce5Co19) phases, and no A2B7 (Ce2Ni7 and Gd2Co7) phase, in the La4MgNi18Al alloys. The substitution of Al clearly led to the increased abundance of the A5B19 phase and the disappearance of the A2B7 phase. Cu and Co exhibited similar roles in the phase composition and contributed to the formation of the A2B7 phase. The substitution of Ni by Al, Cu, or Co led to the increase in the maximum discharge capacity Cmax, which is mainly related to the increase in the cell volume and the abundances of the A2B7 and A5B19 phases. With increasing annealing temperature, the Cmax of the La4MgNi18M alloy electrodes first increased and then decreased, with the highest value obtained at an annealing temperature of 1223 K. The change trend in the cycling stability of the La4MgNi18M alloy electrodes was inversely proportional to that of the abundance of the LaNi5 phase. The substitution of Ni by Al, Cu, or Co led to the enhancement in the cycling stability of the alloy electrodes, which was related to the improvement in the corrosion resistance and anti-pulverization ability.

Microstructural evolution and performance of hydrogen storage and electrochemistry of Co-added La0.75Mg0.25Ni3.5−xCox (x = 0, 0.2, 0.5 at%) alloys

Microstructure, hydrogen storage and electrochemical performances of Co-added La0.75Mg0.25Ni3.5−xCox (x = 0, 0.2, 0.5at%) alloys are studied. XRD and rietveld refinement results suggest that the samples are mainly composed of (LaMg)Ni3, (LaMg)2Ni7 and LaNi5 phases, Co substitution for Ni changes the phase abundance, but not the phase composition. With the rising of Co content, the amount of (LaMg)2Ni7 phase decreases, but the amount of LaNi5 phase increases, while the amount of (LaMg)Ni3 phase firstly increases and then decreases. The alloys reversibly absorb and desorb hydrogen at 298K smoothly. When Co content is 0.2at%, the hydrogen absorption capacity reaches the maximum value of 1.14H/M, and the absorption capacities reach 1.09H/M and 1.03H/M in the first minute at 298K and 323K, respectively. Electrochemical performance measurement results show that La0.75Mg0.25Ni3.5−xCox alloys are completely activated within 2 cycles, and the cyclic stability of La0.75Mg0.25Ni3.3Co0.2 alloy approaches 63.7% after 100 charge/discharge cycles, which is higher than that (S100 = 60%) of La0.75Mg0.25Ni3.0Co0.5 alloy. Thus, the La0.75Mg0.25Ni3.3Co0.2 alloy exhibits optimum comprehensive properties of hydrogen storage and electrochemistry.

Inhomogeneous Superconducting Behaviour in hbox {La}_{5}hbox {Ni}_{2}hbox {Si}_{3}

The superconducting phase transition at T_mathrm{c} = 2.3 K was observed for the electrical resistivity rho ({T}) and magnetic susceptibility chi (T) measurements in the ternary compound La_{5}hbox {Ni}_{2}hbox {Si}_{3} that crystallizes in the hexagonal-type structure. Although a single-phase character with the nominal stoichiometry of the synthesized sample was confirmed, a small trace of the La–Ni phase was found, being probably responsible for the superconducting behaviour in the investigated compound. The magnetization loop recorded at {T} = 0.5 K resembles a star-like shape which indicates that the density of the critical current can be strongly suppressed by a magnetic field. The low-T _{rho }(T) and specific heat {C}_mathrm{p}({T}) data in the normal state reveal simple metallic behaviour. No clear evidence of a phase transition to any long- or short-range order was found for C_mathrm{p}(T) measurements in the T-range of 0.4–300 K.

Effect of rare earth element substitution for lanthanum on structure and electrochemical characteristic of La0.8Mg0.2Ni3.3Al0.3Mo0.2 hydrogen storage alloys

The microstructure and electrochemical properties of La0.8−xMg0.2RExNi3.3Al0.3Mo0.2(x = 0.1; RE = Ce, Nd, Pr, Y, Gd, and Er) hydrogen storage electrode alloys have been investigated systematically. The results of X-ray diffraction show that the matrix phase structure of the alloys is composed of the LaNi5 phase and the La2Ni7 phase. The partial substitution of Lanthanum by rare earth elements can improve the cell volume of the LaNi5 phase. The electrochemical properties of the alloys are improved obviously. The maximum discharge capacity is improved with Ce, Nd, Pr, Er, and Y substitution. Er and Y substitution promote the cyclic durability of the alloy. Nd and Pr can improve the high-rate ability of the alloy electrodes. The electrochemical impedance spectroscopy test shows that the charge-transfer resistance at the surface of the alloy electrodes decreases obviously with Nd and Pr substitution.