Crystallographic and electrochemical characteristics of La0.7Mg0.3Ni5.5? x (Al0.5Mo0.5) x ( x =0 to 0.8) hydrogen storage alloys

The structure, hydrogen storage property, and electrochemical characteristics of the La_0.7Mg_0.3Ni_5.5−x (Al_0.5Mo_0.5) _x (x=0, 0.2, 0.4, 0.6, 0.8) hydrogen storage alloys have been investigated systematically. It has been found by X-ray powder diffraction and Rietveld analysis that the alloys are multiphase and consist of impurity Ni phase and two main crystallographic phases, namely, the La(La, Mg)₂Ni₉ phase and the LaNi₅ phase, and the lattice parameters and the cell volumes of both the La(La, Mg)₂Ni₉ phase and the LaNi₅ phase increase with increasing Al and Mo content in the alloys. The P-C isotherm curves indicated that the hydrogen storage capacity of the alloy first increases and then decreases with increasing x, and the equilibrium pressure decreases with increasing x. The electrochemical measurements show that the maximum discharge capacity first increases from 298.5 (x=0) to 328.3 mAh/g (x=0.6) and then decreases to 304.7 mAh/g (x=0.8). The high rate dischargeability (HRD) of the alloy electrodes increases lineally from 65.4 pct (x=0) to 86.6 pct (x=0.8) at the discharge current density of 1200 mA/g. Moreover, the exchange current density of the alloy electrodes also increases monotonously with increasing x by the linear polarization curves. The hydrogen diffusion coefficient in the alloy bulk, D, increases with increasing Al and Mo content and thus enhances the low-temperature dischargeability (LTD) of the alloy electrodes.     

Microstructure and electrochemical properties of LaNi4–xFeMnx (x=0–0.8) hydrogen storage alloys

In order to reduce the cost of LaNi5 based hydrogen storage alloys, effect of substitution of Mn for Ni on structural and electro-chemical properties of LaNi4-xFeMnx(x=0-0.8) hydrogen storage alloys was studied systematically. X-ray diffraction (XRD) and scanning electron microscope (SEM) showed that LaNi5 and La2Ni7 phases were invariably present in all alloy samples, and when x≥0.4, (Fe,Ni) phase was observed. Electrochemical studies revealed that the discharge capacity reached a maximum value of 306.4 mAh/g when x=0.2 and the cycling stability decreased with the increase of x.With the increase of Mn content, hydrogen diffusion coefficient decreased, whereas high rate discharge-ability (HRD) and exchange current density first increased slowly when x≤0.2 and then decreased markedly when x=0.8,indicating that electrochemical reaction on the surface of alloy electrodes had strong influence on kinetic property.     

Influence of magnesium on electrochemical properties of RE3-xMgx(Ni0.7Co0.2Mn0.1)9（x=0.5-1.25） alloy electrodes

RE3-xMgx(Ni0.7Co0.2Mn0.1)9 (x=0.5-1.25) alloys were prepared by induction melting and the influence of the partial substitution of RE (where RE stands for La-rich mischmetal) by Mg on the hydrogen storage and electrochemical properties of the alloys were investigated systematically. These alloys mainly consisted of three phases, La(Ni,Mn,Co)5 phase, La2Ni7 phase and Mg2Ni phase. The P-C-T isotherms showed that with Mg content increasing in the alloys, the hydrogen storage capacity first increased and reached the maximum capacity of 1.36 wt.% when x=1.0, and then decreased with x increasing further. Electrochemical studies revealed that the discharge capacity reached the maximum value of 380 mAh/g and the alloy electrode presented better cyclic stability when RE/Mg=2. The high rate discharge ability of the alloy electrodes was also improved by the substitution of Mg for RE. The RE2Mg(Ni0.7Co0.2Mn0.1)9 alloy exhibited better hydrogen absorption kinetics (x=1.0).)     

Phase structure and electrochemical properties of non-stoichiometric La0.7Ce0.3(Ni3.65Cu0.75Mn0.35Al0.15(Fe0.43B0.57)0.10)x hydrogen storage alloys

Phase structure and electrochemical characteristics of Co-free La0.7Ce0.3(Ni3.65Cu0.75Mn0.35Al0.15(Fe0.43B0.57)0.10)x (0.90≤x≤1.10) al-loys were investigated. When x was 0.90, the alloy was composed of LaNi5, La3Ni13B2 and Ce2Ni7 phases. The Ce2Ni7 phase disappeared, and the abundant of La3Ni13B2 phase decreased when x increased to 0.95. When x was 1.00 or higher the alloys consisted of LaNi5 phase. The lat-tice parameter a and the cell volume V of the LaNi5 phase decreased, and the c/a ratio of the LaNi5 phase increased with x value increasing. Maximum discharge capacity of the alloy electrodes first increased and then decreased with x value increasing from 0.90 to 1.10, and the highest value was obtained when x was 1.00. High-rate dischargeability at the discharge current density of 1200 mA/g increased from 50.7% (x= 0.90) to 64.1% (x=1.10). Both the charge-transfer reaction at the electrode/electrolyte interface and the hydrogen diffusion in the alloy were responsible for the high-rate dischargeability. Cycling capacity retention rate at 100th cycle (S100) gradually increased from 77.3% (x= 0.90) to 84.6% (x=1.10), which resulted from the increase in Ni content and the c/a ratio of the LaNi5 phase with x value increasing.     

Study on structure and electrochemical properties of the (LaGdMg)Ni3.35-xCoxAl0.15 (x=0-2.0) hydrogen storage alloys

Hydrogen storage alloys (LaGdMg)Ni_3.35-xCo_xAl_0.15 (x=0, 0.1, 0.3, 0.5, 1.0, 1.5, 2.0) were prepared by induction melting followed by annealing treatment in argon atmosphere. The effects of partly replacing Ni by Co element in (LaGdMg)Ni_3.35Al_0.15 on the phase structure and electrochemical properties of (LaGdMg)Ni_3.35-xCo_xAl_0.15 alloys were investigated. Structure analysis showed that the alloys consisted of Ce₂Ni₇-type (Gd₂Co₇-type), CaCu₅-type, Pr₅Co₁₉-type, PuNi₃-type phase structure. The addition of Co element obviously reduced the contents of CaCu₅-type phase and increased the contents of Ce₂Ni₇-type phase. However, Pr₅Co₁₉-type and CaCu₅-type phase obviously increased with the high content of Co. Rietveld analysis showed that the c-axis lattice parameters and cell volumes of the component phases increased with increasing Co content. The electrochemical measurements showed that as the Co content increased, the maximum discharge capacity and the cyclic stability of the annealed alloys both first increased then decreased. The (LaGdMg)Ni_3.05Co_0.3Al_0.15 alloy electrode exhibited the maximum discharge capacity (392.92 mAh/g), and the (LaGdMg)Ni_1.85Co_1.0Al_0.15 alloy electrode showed the best cyclic stability (S₁₀₀=96.1%).     

Glycine-nitrate auto-combustion synthesis and magnetic properties of nanocrystalline NdAlxFe1-xO3 perovskites

The effect of substitution of Fe³⁺ by Al³⁺ on the structure and magnetic properties of NdAl_xFe_1-xO₃ perovskite nano-powders(x=0.0,0.1,0.2,0.3,0.4,and 0.5) prepared by the glycine-nitrate auto-combustion method was studied.All samples were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FT-IR),and energy dispersive X-ray spectroscopy(EDX).The magnetic properties of the samples ...     

Effect of chromium on magnetic properties and corrosion resistance of LaFe11.5Si1.5 compound

Effects of Cr addition on magnetic and corrosion properties of LaFe11.5-xCrxSi1.5 (x=0.1, 0.3, 0.4) magnetic refrigerants were investigated. It was found that the addition of Cr slightly decreased the magnetic entropy change, but it was effective in increasing corrosion resistance of La-Fe-Si compounds within the composition range examined. Corrosion measurements showed that corrosion current density of these La-Fe-Si compounds in distilled water decreased from 2.6×10-6 to 8.7×10-7 A/cm2, with x increasing from 0 to 0.3, while magnetic entropy change in LaFe11.5-xCrxSi1.5 compounds did not change significantly (-ΔSmax was 18.0, 17.0, 13.6, 11.1 J/(kg·K)) under 2 T for x=0, 0.1, 0.3, 0.4, respectively). Surface optical microstructures of compounds after corroded showed that corrosion took place at grains and grain boundaries simultaneously and surface concentration of corroded points on LaFe11.5-xCrxSi1.5 (x=0.1, 0.3, 0.4) compounds reduced obviously.     

Effect of reduced graphene oxide-supported copper addition on electrochemical properties of La0.7Mg0.3Ni2.8Co0.5 electrodes

The reduced graphene oxide-supported copper(Cu@rGO) nanocomposite was introduced to improve the electrochemical properties of La_(0.7)Mg_(0.3)Ni_(2.8)Co_(0.5)alloy electrodes.Experimental results show that adding Cu@rGO nanocomposite with mass fractions of x wt%(x=0,3,6 and 9) to the alloy electrodes provides electrodes with maximum discharge capacities of 368.9 mAh/g(x=0),373.2 mAh/g(x=3),407.3 mAh/g(x=6) and 398.6 mAh/g(x=9),and high-rate dischargeabilities at a discharge current density of1200 mA/g of 40.5%(x=0),64.0%(x=3),82.0%(x=6) and 76.0%(x=9).The addition of Cu@rGO nanocomposite also provides alloy electrodes with hydrogen diffusion coefficients of 3.7×10~(-10) cm~2/s(x=0),4.1×10~(-10) cm~2/s(x=3),4.2×10~(-10) cm~2/s(x=6) and 4.0×10~(-10) cm~2/s(x=9).Clearly,the addition of 6 wt%Cu@rGO nanocomposite not only increases the electrochemical capacity of La_(0.7)Mg_(0.3)Ni_(2.8)Co_(0.5) alloy electrodes,but also improves their electrochemical kinetic properties.     

Hydrogen storage properties of mechanically milled La2Mg17-x wt.% Ni （x=0, 50, 100, 150 and 200） composites

Melting method was used to obtain La2Mg17 alloy,and then Ni powder was added by mechanical alloying method.The kinetics of hydriding process and electrochemical properties of La2Mg17-x wt.%Ni(x=0,50,100,150,200) composites were investigated.X-ray diffraction(XRD) and scanning electron microscopy(SEM) analyses showed that the crystal structure of composite alloy gradually transformed into amorphous phase by the effect of ball milling and Ni powders.The research of hydrogen absorption properties found that La2Mg 17-50 wt.%Ni reached the highest hydrogen absorption than other alloys with more addition of Ni content,reached to 5.796 wt.% at 3 MPa,and up to 5.229 wt.% merely in 2 min,which revealed that the amorphous phase reduced the H occupation of the lattice clearance,resulting in the decline of hydrogen absorption capacity.The electrochemical tests indicated that the maximum discharge capacity increased to 353.1 mAh/g at 30 oC,however,the cycle stability decreased considerably.A series of kinetic measurements demonstrated that the controlling steps of electrochemical process of La 2 Mg 17-x wt.%Ni alloys transferred from hydrogen diffusion on alloy bulk(x=50,100) to hydrogen diffusion on both alloy bulk and surface(x=150,200).     

Electrical and CO-sensing properties of NdFe1-xCoxO3 perovskite system

NdFe_1-xCo_xO₃ (x=0.0-0.5) powders were prepared by a sol-gel citric method. X-ray diffraction was used to confirm the phase composition of the powders. All the samples are orthorhombic structure. The unit cell volume and grain size decreased with an increase of Co content x. The conduction type of the NdFe_1-xCo_xO₃ perovskite oxides changed with the increasing Co content x. When x<0.3, the oxides showed p-type conduction behavior, and then changed to n-type when x>0.3. All the sensors presented higher responses and lower optimal operating temperatures. The highest response to 0.03% CO gas reached 1215% at 170 °C for NdFeO₃ sensor; however, Co²⁺ doping in NdFeO₃ did not improve the gas responses.     

Electrode Characteristics of MmNi_5－type Alloys for Nickel－metal HydrideBatteries

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Electrochemical performances of four lanthanum transition-metal complex oxides

As novel negative electrode materials for alkaline batteries, the electrochemical properties of four lanthanum transition-metal (La-TM) complex oxides LaTiO₃, LaVO₄, LaCrO₃ and LaMnO₃ were investigated. X-ray diffraction (XRD) and scanning electron microscope (SEM) were employed to characterize their microstructures. All the La-TM oxides were made up of single phases. Electrochemical measurements showed that the maximum discharge capacities of LaTiO₃, LaVO₄, LaCrO₃, and LaMnO₃ electrodes at 303 K were 367, 187, 318, and 278 mAh/g, respectively. X-ray photoelectron spectroscopy (XPS) and XRD Rietveld analysis were carried out to discuss the electrochemical reaction mechanism. Electrode kinetics was studied by electrochemical impedance spectrum (EIS). The results showed that the maximum discharge capacity was directly related to the charge-transfer resistance (R_ct) of La-TM oxide electrode. The cyclic properties of the four oxides should be further improved and the discharge capacity of LaMnO₃ (about 96 mAh/g) was the highest after 10^th charge/discharge cycles.     

Microstructure and electrochemical characteristics of La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75-x（V0.81Fe0.19）x hydrogen storage alloys

Microstructure and electrochemical characteristics of La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75-x(V0.81Fe0.19)x hydrogen storage alloys were investigated. XRD indicated that La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75-x(V0.81Fe0.19)x alloys consisted of a single phase with CaCu5-type structure, and the lattice parameter a and cell volume V increased with increasing x value. The maximum discharge capacity first increased from 319.0 (x=0) to 324.0 mAh/g (x=0.05), and then decreased to 307.0 mAh/g (x=0.20). The high-rate dischargeability at the discharge current density of 1200 mA/g first increased from 52.1% (x=0) to 59.1% (x=0.15), and then decreased to 55.4% (x=0.20). The hydrogen diffusion in the bulky alloy was responsible for the high-rate dischargeability. Cycling stability first increased with increasing x from 0 to 0.10 and then decreased when x increased to 0.20, which was resulted from the synthesized effect of the improvement of the pulverization resistance and the decrease of corrosion resistance.     

Characterization of A-site excessive perovskite La0.7-xSmx＋0.02Ca0.3CrO3-δ

La0.7-xSmx+0.02Ca0.3CrO3-δ(0≤x≤0.4) powders with A-site excessive perovskite structure were synthesized by auto-ignition process and characterized. X-ray diffraction (XRD) patterns of samples after sintering at 1400℃ for 4 h were indexed as tetragonal structure. The relative densities were all above 96% although decreased slightly with the increasing content of samarium, indicating that the excessive A-site element was helpful to enhance their sinterability. Conductivities of the specimens in air increased with increasing content of samar-ium. The conductivity of La0.6Sm0.12Ca0.3CrO3-δ was 33.6 S/cm in air at 700 ℃ which was about 1.7 times as high as that of La0.7Ca0.3CrO3-δ (20.1 S/cm). Average thermal expansion coefficients (TECS) of the specimens increased from 11.06×10-6 to 12.72×10-6 K-1 when x in-creased from 0 to 0.4, and they were close to that of Y doped ZrO2 (YSZ). La0.7-xSmx+0.02Ca0.3CrO<3-δ>(0.1≤x≤0.3) were good choices for in-termediate temperature solid oxide fuel cells (IT-SOFCs) interconnect materials.     

Influence of partial substitution of cerium for lanthanum on magnetocaloric properties of La_(1–x)Ce_xFe_(11.44)Si_(1.56) and their hydrides

The structure and magnetocaloric properties of La1–xCexFe11.44Si1.56 and their hydrides La1–xCexFe11.44Si1.56Hy（x=0, 0.1, 0.2, 0.3, 0.4） were investigated.The samples crystallized mainly in the cubic Na Zn13-type structure with a small amount of α-Fe phase as impurity.The lattice constants and Curie temperature presented the same change tendency with increasing of Ce content.For the hydrides, the influence of Ce content on lattice constants was weakened and the values of H concentration y were approximate to be 1.56.The La1–xCexFe11.44Si1.56 compounds exhibited large values of isothermal entropy change –ΔSm around the Curie temperature TC under a low magnetic field change of 1.5 T.The value of –ΔSm increased and then decreased with increasing Ce content, reached the maximum, 26.07 J/kg·K for x=0.3.TC increased up to the vicinity of room temperature by hydrogen absorption for the Ce substituted compounds, but TC only slightly decreased with increasing Ce content.The first-order metamagnetic transition was still kept in the hydrides and the maximum values of –ΔSm were lower than those of the La1–xCexFe11.44Si1.56 compounds, but still remained large values, about 10.5 J/kg K under a magnetic field change of 1.5 T.The values of –ΔSm were nearly independent of the Ce content and did not increase with increasing x for the hydrides.The La1–xCexFe11.44Si1.56Hy（x=0–0.4） hydrides exhibited large magnetic entropy changes, small hysteresis loss and effective refrigerant capacity covered the room temperature range from 305 to 317 K.These hydrides are very useful for the magnetic refrigeration applications near room temperature under low magnetic field change.     

Ce1–xSmxO2–δ-attapulgite nanocomposites：synthesis via simple microwave approach and investigation of its catalytic activity

Ce1–x Smx O2–δ-attapulgite（ATP） nanocomposites were successfully prepared via a facile microwave approach.This was a facile and rapid process requiring only low power of microwave irradiation（160 W）.The catalytic performance of the Ce1–x Smx O2–δ-ATP nanocomposites with different Sm contents for degradation of methylene blue（MB） was systematically evaluated.The Ce1–x Smx O2–δ-ATP nanocomposites showed enhanced catalytic activities compared with pure CeO2/ATP.Specifically,the catalytic activities of Ce1–x Smx O2–δ-ATP nanocomposites increased with increase in Sm content from x=0.0 to 0.3.The introduction of an optimal amount of Sm3＋into CeO2 contributed to the formation of structure defects and electronic defects in the oxide lattice,which could increase concentration of oxygen vacancies.However,further increasing Sm content to x=0.4 induced the formation of more agglomerates,leading to decreased catalytic activity.It was believed that this facile,rapid microwave-assisted strategy was scalable and could be applied to synthesize other nanocomposites for different applications.     

Effect of Thermal Treatment on Formation of High Magnetic Parameters of Sintered Magnets Dd-Fe-B

The present paper is dedicated to study effect of thermal treatment parameters on the properties (residual magnetic induction fir, coercive force on magnetization _iH_c, temperature coefficient of magnetic induction α_b within the temperature range 300–373 K) of sintered permanent magnets [Dd_1–x(Dy, Tb, Ho)_x]₁₅(Fe_1–yCo_y)_bal(Al,Cu,Ga,Ti)_0.1–1.4B_5.0–8.5 (at.%), where x=0.2–0.4; y = 0.2–0.3; Dd - didymium. For the magnets (Dd_1–xDy_x)₁₅(Fe_1–yCo_y)_baiB_5.0–5.6 discontinuities were observed at demagnetization curves caused by appearance of magnetic phases with reduced magnetic anisotropy. _iH_c value nearly does not depend on temperature of thermal treatment within the range 750–1275 K at increasing of boron content (7.0–7.5at.%). Magnets doping by such elements as aluminium, copper, gallium shifts optimal temperature of the last step of thermal treatment from 900 K to 725–825 K, at the same time magnetic properties (B_r, _iH_c α_b) improve, especially with increasing of Co and Dy content. It was possible to attain the following properties for the magnets (Dd_0.6Dy_0.4)₁₅(Fe_0.74Co_0.26)_bai(Al,Cu,Ga)_1.1B_8.5 after optimal thermal treatment {1175 K (7, 2 ks) with further cooling at the rate 1–2 K/min, then 900 K (3.6 ks) - hardening + 775 K (3.6 ks) - hardening}: B_r= 1,0 T, _iH_c = 1600 kA/m, BH_max = 192 kJ/m³, α_b= −0,024 %/K in the temperature interval 293–373 K.     

Microstructure Related Hydrogen Storage Capacity of Cast Mischmetal-Nickel Alloys Substituted with Aluminium,Manganese and Tin

Abstract

The morphology and compositions of the phases present in the microstructure of cast hydrogen storage MmNi_5-xAl_x (x= 0.4 and 0.8) MmNi_4.6 Sno₄ Mn, alloys (Mm = Indian Mischmetal) have been studied. Al, Mn and Sn substitutions for Ni in MmNis produce two-phase microstructures. The hydrogen storage capacity of these alloys is related with the volume fraction of the matrix phase. Higher the matrix volume fraction, higher the hydrogen storage capacity. The hydride forming elements that constitute Mm are present in greater proportion in the major constituent matrix phase of the two-phase structure. Only trace amounts of these elements are found in the precipitate phase in the Al- and Mn substituted alloys. However, for the Sn-substituted composition, the proportion of these elements is nearly same in matrix and precipitate phase.     

Effect of Al82.8Cu17Fe0.2 alloy doping on structure and magnetic properties of SmCo5-based ribbons

This work tries to improve the magnetic properties by multi-element doping in the form of a ternary alloy.SmCo₅₊χwt%Al-Cu-Fe(x=0-7)ribbons melt-spun at 40 m/s were produced by adding Al_82.8Cu₁₇Fe_0.2alloy into SmCo₅ matrix,and their phases,microstructure,and magnetic properties were investigated.The results show that both x=0 and 3 ribbons form a cellular microstructure.Al-Cu-Fe addition reduces the content of the Sm₂(Co,M)₇ cell wall,narrows its width,and forms the local disordered micro-regions and solute-segregation nanoclusters in the Sm(Co,M)₅ grains.With x increasing to5,Al-Cu-Fe addition promotes the phase separation between and within grains of the SmCo₅-based alloy.The Al-Cu-Fe addition can simultaneously improve the coercivity and magnetization of the SmCo₅-based ribbons,in particular,the magnetization of the x=3 ribbons increases by 35%,while the coercivity of the x=5 ribbons increases by 3.9 times.Finally,the microstructure evolution models are built up,and the relationship between the microstructure and the magnetic properties is discussed.     

Effect of cerium on structure,magnetism and magnetostriction of Fe81Ga19 alloy

FeGa alloy is a new kind of magnetostrictive material, and rare-earth cerium can improve its magnetostrictive property.(Fe_(81)Ga_(19))_(100-x)Ce_x(x = 0, 0.3 at%, 0.7 at%, 1 at%) samples were prepared by doping cerium in Fe_(81)Ga_(19) alloy. Their microstructures and phases were studied, and valence electronic structures were investigated. Electromagnetic parameters, such as coercivity, saturation magnetization,remnant magnetization and saturation magnetostrictive coefficients(λ_s) of every sample were measured.Cerium atoms are distributed at grain boundaries, and the Ce-doped alloys remain the A2 structure of FeGa alloy. When x is 0.7, the value of saturation magnetism is 217.08 emu/g, which is the maximum in the Ce-doped samples. The equivalent half length of single bond is the maximum also, and reaches to0.11380 nm. At the same time, the number of covalent electrons is 3.5672, and is the minimum of the Cedoped samples. Its As is the largest in the four samples. The change of As results in the change of equivalent half length of single bond in Ce-doped alloy.