•A magnetic palygorskite based bimetallic Pal@Fe3O4@PdRu catalyst was prepared.•The catalyst show good performance in the degradation of nitroarenes and azo dyes.•The bimetallic nanocatalyst can be recycled by applying an external magnetic field.•The as-prepared nanocatalyst indicated improved catalytic activities.In this paper, a novel magnetic PdRu alloy-coated palygorskite(Pal)-based nanocatalyst was successfully prepared, which was explored for the hydrogenation reaction of nitroarenes and organic dyes. The morphology and structure details of Pal-Fe3O4-PdRu were revealed by different modern characterization methods. The metal loading for the Pal-Fe3O4-PdRu was 16.81 wt.%, and the atomic ratio of Pd:Ru was 0.65:0.35. In comparison with the monometallic Pal-Fe3O4-Pd or Pal-Fe3O4-Ru, the designed Pal-Fe3O4-PdRu nanocatalyst showed the improved performance in the reduction of 4-nitrophenol, where sodium borohydride was used as reducing agent. More importantly, this catalyst still showed good recycle-ability and reusability in the hydrogenation of several other nitroarenes and azo dyes, which indicated the potential applications in environmental issues.Download high-res image (154KB)Download full-size image

•Substitution of Ni by Al contributes to the formation of A5B19 phase.•Cu and Co are beneficial to the formation of A2B7 phase.•Cmax firstly increases and then decreases with increasing annealing temperature.•Phase composition plays more important role on cycling stability than other factors.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.

•Sm, Gd and Y contribute to the formation of A5B19 phase, especially Ce5Co19.•Pr and Nd promote the formation of A2B7 phase.•Cmax firstly increases and then decreases with increasing annealing temperature.•Substitution of La by Pr, Nd, Sm, Gd or Y causes the decrease of HRD.•Phase composition plays more important role on cycling stability than other factors.Adjusting the rare earth (RE) compositions in the RE–Mg–Ni alloys can effectively improve the electrochemical hydrogen storage performances of the alloy electrodes. Herein, A5B19 type hydrogen storage alloys with the elemental composition of La3RMgNi19 (R = La, Pr, Nd, Sm, Gd and Y) were prepared by induction melting and subsequent annealing. The phase transformation and electrochemical hydrogen storage performances of La3RMgNi19 alloys were investigated in detail. X-ray diffraction analysis shows that La3RMgNi19 alloys contains AB5, A2B7 (Ce2Ni7 and Gd2Co7) and A5B19 (Pr5Co19 and Ce5Co19) phases, and the increase of annealing temperature obviously reduces the phase abundance of LaNi5 phase. Sm, Gd and Y contribute to the formation of A5B19 phase, especially Ce5Co19, and Pr and Nd promote the formation of A2B7 phase for La3RMgNi19 alloys. With increasing annealing temperature, the maximum discharge capacity (Cmax) of La3RMgNi19 alloy electrodes first increases and then decreases, and the highest value of Cmax is achieved as the annealing temperature is 1223 K. This evolution trend of the Cmax is inversely proportional to that of LaNi5 phase abundance. The substation of La by Pr, Nd, Sm, Gd or Y causes the decrease of Cmax, which is mainly ascribed to the decrease of cell volume. Due to the decrement of LaNi5 phase, the cycling stability increases at first when the annealing temperature is below 1223 K. However, when annealing temperate further increases to 1273 K, the cycling stability decreases, which is caused by the increment of LaNi5 phase. It is worth noting that the phase composition (LaNi5 phase abundance) plays more important role than other factor. The slight decrement of high-rate dischargeability resulted from the substitution of La by Pr, Nd, Sm, Gd or Y should be attributed to the combined effect of advantageous and disadvantageous factors.

In this paper, we report a new Gd2Co7-type Sm1.6Mg0.4Ni7 compound as a hydrogen storage material with a special hydrogen absorption/desorption process and good hydrogen storage ability. The Gd2Co7-type Sm1.6Mg0.4Ni7 compound absorbs 1.88 wt% H2 within 17 min at 298 K under 10 MPa H2. Meanwhile, the hydrogen absorption speed accelerates to 3.4 min after 20 hydrogenation/dehydrogenation cycles with a 1.44 wt% H2 under 3 MPa H2. Especially, the capacity retention of the compound is 99.3% at the 100th cycle. We found the hydrogen absorption/desorption of the compound undergoes two equilibrium stages, relating to the transformation of H2 between H-solid solution phase and hydride phase with a lower rate and higher enthalpy change at the lower concentration H2 stage, and the direct conversion between H2 and the hydride phase with a higher rate and lower enthalpy change at the higher concentration H2 stage. The two step mode lowers the inner-molecular strain and mismatch in subunit volumes of the compound in hydrogen absorption/desorption, caused by the transformation of H2 at the lower concentration of H2 stage, thus leading to good structural stability and excellent cycling stability. The new insights are expected to provide viable intermetallic materials as high-pressure tank materials for hydrogen storage with nice hydrogen storage properties.

In this study, a simple hydrothermal method has been developed to prepare Ti3C2Tx from Ti3AlC2 as a high-performance electrode material for supercapacitors. This method is environmentally friendly and has a low level of danger. The morphology and structure of the Ti3C2Tx can be controlled by hydrothermal reaction time, temperature and NH4F amounts. The prepared Ti3C2Tx was characterized by X-ray diffraction, field emission scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and Brunauer-Emmet-Teller. The results show that the prepared Ti3C2Tx is terminated by O, OH, and F groups. The electrochemical properties of the Ti3C2Tx sample exhibit specific capacitance up to 141 Fcm−3 in 3 M KOH aqueous electrolyte, and even after 1000 cycles, no significant degradation of the volumetric capacitance was observed. These results indicate that the Ti3C2Tx material prepared by this hydrothermal method can be used in high performance supercapacitors.

•{101¯2} extension twins form in a Mg–1 wt.% Y alloy with a true strain of 1%.•Extension twins improves electrochemical corrosion properties of a Mg–1 wt.% Y alloy.•{101¯2} twins vary pitting potential, film formation and charge transfer resistance.•The reasons root in a preferential oxide layer and low twin boundary energy.The effect of extension twinning formed during compression deformation on the corrosion properties of an Mg–1 wt.% Y alloy was investigated using electrochemical tests. The corrosion morphology evolution after immersion in 0.9 wt.% NaCl aqueous solutions for various times has been analyzed by scanning electron microscope. The electron back-scatter diffraction result shows the {101¯2} extension twins appear in the deformed Mg–1 wt.% Y alloy with a true strain of 1%. The extension twinning accelerates the formation of oxide film and increases charge transfer resistance, resulting in the improvement of corrosion properties. However, it hardly affects the occurrence of microcracks in grain boundaries. The main reasons root in a preferred formation of homogeneous oxide layer in twinning area and low twin boundary energy.

W0.42Fe0.58 alloy, instead of pure W and Fe, was used to substitute Co in LaNi3.70Co0.2Mn0.30Al0.15Cu0.65 alloy to improve the overall electrochemical properties with the decrement of the cost. Microstructures and electrochemical characteristics of LaNi3.70Co0.2–xMn0.30Al0.15Cu0.65(W0.42Fe0.58)x (x=0–0.20) hydrogen storage alloys were characterized. X-ray diffraction patterns and backscattered electron images indicated that the pristine alloy was LaNi5 phase, while the alloys containing W0.42Fe0.58 were made of LaNi5 matrix phase and W phase. The relatived abundance of W phase increased with the increase in x value. Lattice parameters a, c, c /a and cell volume V of LaNi5 phase increased with increasing x value. Activation property of the alloy electrodes was improved by substituting Co by W0.42Fe0.58. As x increased from 0 to 0.20, maximum discharge capacity of alloy electrodes decreased from 335.4 (x=0) to 320.7 mAh/g (x=0.20). The high-rate dischargeability at the discharge current density of 1200 mA increased from 59.8% (x=0) to 76.8% (x=0.10), and then decreased to 64.7% (x=0.20). The cycling capacity retention rate at the 100th cycle decreased from 80.4% (x=0) to 55.8% (x=0.20), which should be ascribed to the degradation of the corrosion resistance and electrochemical kinetics of alloy electrodes.XRD patterns of LaNi3.70Co0.2–xMn0.30-Al0.15Cu0.65(W0.42Fe0.58)x alloys (a) XRD patterns for x=0–0.20; (b) Rietveld analysis pattern for x=0.15

•The area fraction of Mg matrix is increased with increasing the pressure.•Al concentration is increased in Mg17Al12 compound after high pressure treatment.•Both the hardness and Young’s modulus are increased with increasing the pressure.•The corrosion properties of SHP-2 GPa-800 sample are improved greatly.•The high corrosion resistance is related to the formation of fine oxide film.The aim of this study was to investigate the effects of super-high pressure solidification (2 and 4 GPa) on microstructures, nano-mechanical behaviors and corrosion properties of Mg-30 wt.% Al alloy. The lattice parameter (a) of Mg matrix is decreased and the c/a value is increased owing to the increased Al concentration in Mg matrix. In contrast to the as-cast sample or other super-high pressure samples, the Mg matrix is more homogeneous and the net-like eutectic phase becomes finer after super-high pressure solidification at 800 °C under 2 GPa. In addition, the area fraction of eutectic phase is reduced with increasing the exterior pressure and temperature during the solidification, whilst the Al concentration in both the Mg matrix and the eutectic phase are enhanced. The nanoindentation results indicate that both the hardness and Young’s modulus are sensitive to the solidification pressure and temperature. The Tafel curves and electrochemical impedance spectroscopes results reveal the corrosion properties of the sample at 800 °C under 2 GPa are remarkably improved due to the formation of a compact and continuous oxide layer.

Phase compositions, morphologies and hydrogen storage properties of the as-cast and copper-mould-cast LaMg4Ni alloys were studied. The dehydriding onset temperature of the as-cast alloy hydride was about 500 K, which was at least 50 K higher than that of the copper-mould-cast one, and the copper-mould-cast alloy hydride had a faster dehydriding rate compared with as-cast one. Additionally, the copper-mould-cast alloy could uptake 2.85 wt.% hydrogen, which was 95.0% of saturated hydrogen storage capacity at room temperature. While only 1.80 wt.% hydrogen (60% of saturated capacity) was absorbed for the as-cast alloy under the same conditions. The reversible hydrogen storage capacities and plateau hydrogen pressures of the two alloys were close. X-ray diffractions and scanning electron microscopy results indicated that similar thermodynamic property of the two alloys should be ascribed to the same hydrogen storage phase, Mg and Mg2Ni. The better hydrogen sorption kinetics of copper-mould-cast alloy should be ascribed to the more uniform phase distribution compared with that of the as-cast one.TPD curves of as-cast and copper-mould-cast LaMg4Ni alloys

Hydrogen storage properties of 2LiNH2-MgH2 system were improved by adding lanthanum hydride (LaH3), and the role of LaH3 in hydrogen sorption process of Li-Mg-N-H system was investigated. Temperature programmed sorption results showed that the addition of lanthanum hydride reduced the dehydriding/hydriding onset temperature of 2LiNH2-MgH2 system by at least 15 K. Moreover, A 0.053 wt.%/min average rate was determined for the hydrogen desorption of 2LiNH2-MgH2-0.05LaH3 composite, while it was only 0.035 wt.%/min for 2LiNH2-MgH2 system. Hydrogen absorption capacity increased from 1.62 wt.% to 2.12 wt.% within 200 min by adding LaH3 into 2LiNH2-MgH2 system at 383 K. In the dehydrogenation of 2LiNH2-MgH2-0.05LaH3 composite, LaH2 transferred to LaN phase, which reversed to LaH2 in the following hydrogen adsorption process. The reversible reaction of LaH2 effectively promoted the hydrogen sorption of Li-Mg-N-H system. Moreover, the homogenous distribution of fine La hydride was favorable to improving effect of lanthanum hydride.XRD patterns of 2LiNH2-MgH2-0.05LaH3 system after dehydrogenation at different temperatures

Microstructures and electrochemical characteristics of La0.7Ce0.3Ni4.2Mn0.9−xCu0.37(V0.81Fe0.19)x hydrogen storage alloys were investigated. X-ray diffraction and scanning electron microscope results indicate that La0.7Ce0.3Ni4.2Mn0.9Cu0.37 alloy is single LaNi5 phase, and the alloys containing V0.81Fe0.19 consist of LaNi5 matrix phase and V–Mn–Ni secondary phase, and the abundance of secondary phase increases with increasing x value. The activation property of the alloy electrodes is improved by increasing V0.81Fe0.19 content. Maximum discharge capacity of the alloy electrodes changes a little with increasing x value. HRD1200 first increases from 60.4% (x = 0) to 70.8% (x = 0.10), and then decreases to 56.6% (x = 0.20). Cycling stability decreases with increasing x from 0 to 0.20. The adequate substitution of Mn by V0.81Fe0.19 can improve overall electrochemical performances of Co-free high-Mn AB5 alloy.Highlights► Commercial V0.81Fe0.19 is cheaper than pure V, and has lower melt point than pure V. ► Alloys containing V0.81Fe0.19 consist of LaNi5 matrix phase and V–Mn–Ni secondary phase. ► Activation property is improved by increasing V0.81Fe0.19 content. ► Maximum discharge capacity changes a little with increasing x value. ► The alloy with x = 0.10 exhibits the best HRD.

•UHP can enhance the activation and kinetic performance of RE–Mg–Ni-based alloys.•The UHP alloys exhibits more uniform structure than as-cast one.•Reversible hydrogen capacities of UHP alloys are close to that of as-cast one.•Dehydriding temperature of UHP alloy hydride is lower than that of as-cast one.•UHP alloys show faster hydriding/dehydriding kinetics compared with as-cast one.The influences of ultrahigh pressure (UHP, under 5 GPa) on phase compositions, phase morphologies and hydrogen storage properties of LaMg4Ni alloys were studied. The X-ray diffraction patterns show that the as-cast alloy consists of La2Mg17, LaMg2Ni and Mg2Ni phases, whereas a new LaMg3 phase is observed in the UHP samples in addition to LaMg2Ni and Mg2Ni phases. The scanning electron microscopy graphs indicate that the phase distribution is more homogenous in the UHP alloys than in the as-cast one. Additionally, the microstructure of the UHP alloy heat-treated at 973 K is finer than that at 823 K. Both the reversible hydrogen storage capacity and the plateau of hydrogen pressure of the UHP alloys are close to those of the as-cast one. Of particular interest is that both UHP alloys exhibit better activation properties compared with the as-cast alloy. Moreover, the dehydriding onset temperature of the UHP alloys (5 GPa at 973 K) is about 490 K, which is obviously lower than that of the as-cast alloy. The amount of hydrogen desorption in the UHP alloy (5 GPa at 973 K) is 2.69 wt.% at 573 K, which corresponds to 89.6% of the saturated capacity. However, the corresponding values change to 1.75 wt.% and 58.3% in the as-cast alloy, respectively. It is confirmed the UHP treatment is one of effective approaches to tune the hydrogen storage performances of those rare earth–magnesium–nickel alloys.

Microstructures and electrochemical characteristics of LaNi3.55Co0.2−xMn0.35Al0.15Cu0.75(Fe0.43B0.57)x (x = 0–0.20) hydrogen storage alloys were investigated. X-ray diffraction and Backscatter electron results indicate that the pristine alloy is single LaNi5 phase with CaCu5 type hexagonal structure and the alloys containing Fe0.43B0.57 consist of two phases, matrix LaNi5 phase and La3Ni13B2 secondary phase. The abundance of La3Ni13B2 phase increases with the increase of x value. The a and V of LaNi5 phase increase with increasing x value. Maximum discharge capacity of the alloy electrodes monotonically decreases from 330.0 mA h g−1 (x = 0) to 302.2 mA h g−1 (x = 0.20). High-rate dischargeability of the alloy electrodes first increases with increasing x from 0 to 0.10, and then decreases when x increases to 0.20. Both charge-transfer reaction at the electrode/electrolyte interface and hydrogen diffusion in bulky alloys should be responsible for the high-rate dischargeability. Cycling stability decreases with increasing x from 0 to 0.20. The adequate substitution of Co by FeB can improve the overall electrochemical performances and reduce the raw cost of alloy electrode.Highlights► Commercial FeB is cheaper than Co, Fe and B, and has lower melt point than Fe and B. ► The alloys containing Fe0.43B0.57 consist of LaNi5 phase and La3Ni13B2 phase. ► The alloy with x = 0.10 exhibits the best high-rate dischargeability. ► The alloy with x = 0.10 exhibits the best overall electrochemical property. ► Substitution of FeB for Co improves the HRD and reduces the cost.

Microstructures and electrochemical characteristics of La0.7Ce0.3Ni3.75−xCu0.75Mn0.35Al0.15(Fe0.43B0.57)x hydrogen storage alloys have been investigated. X-ray diffraction results indicate that the alloys consist of a single phase with CaCu5-type structure, and lattice parameters c, cell volume V and c/a ratio increase with increasing x value. Maximum discharge capacity of the alloy electrodes first increases from 311.0 mAh/g (x = 0) to 316.0 mAh/g (x = 0.15), and then decreases to 311.0 mAh/g (x = 0.20). High-rate dischargeability at the discharge current density of 1200 mA/g first increases from 51.3% (x = 0) to 60.7% (x = 0.15), and then decreases to 53.6% (x = 0.20). Cycling stability first increases with increasing x from 0 to 0.10 and then decreases when x increases to 0.20, which should be ascribed to the improvement of the pulverization resistance and the deterioration of corrosion resistance.

Microstructures and electrochemical characteristics of La0.7Ce0.3Ni3.75−xMn0.35Al0.15Cu0.75(V0.81Fe0.19)x (x = 0–0.20) hydrogen storage alloys have been investigated. X-ray diffraction patterns and Backscatter electron images indicate that La0.7Ce0.3Ni3.75−xMn0.35Al0.15Cu0.75(V0.81Fe0.19)x alloys consist of a single phase with CaCu5-type structure. The lattice parameter a and cell volume V increase with increasing x value. Maximum discharge capacity monotonically decreases from 320 mAh/g (x = 0) to 299 mAh/g (x = 0.20). The high-rate dischargeability at the discharge current density of 1200 mA/g first increases from 52.6% (x = 0) to 55.6% (x = 0.05), and then decreases to 46.7% (x = 0.20). Cycling stability first increases with increasing x from 0 to 0.10 and then decreases when x increases to 0.20, which is resulted from the combined effect of the improvement of the pulverization resistance and the decrease of corrosion resistance.Highlights► Commercial VFe alloy is cheaper than pure V and Ni. ► Alloys consist of a single CaCu5-type phase, and a and V increase with increasing x. ► The alloy with x = 0.05 exhibits the best high-rate dischargeability. ► The alloy with x = 0.1 exhibits the best cycling capacity retention rate. ► Substitution of VFe for Ni can improve HRD and cycling stability.

Microstructure and electrochemical characteristics of La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75−x(Fe0.43B0.57)x hydrogen storage alloys have been investigated. XRD indicates that La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75 alloy consists of a single LaNi5 phase with CaCu5 structure. The alloys containing FeB are composed of LaNi5 phase with CaCu5 structure as matrix phase and La3Ni13B2 phase as secondary phases, and the abundance of the secondary phase gradually increases with increasing FeB content. As x increases from 0.00 to 0.20, maximum discharge capacity of the alloy electrodes monotonically decreases from 314.0 to 290.4 mAh/g. Cycling stability of the alloy electrodes increases with increasing x value. High-rate dischargeability at the discharge current density of 1200 mA/g first increases from 51.4% (x = 0) to 57.2% (x = 0.10), and then decreases to 52.7% (x = 0.20). The improvement in electrochemical characteristics is ascribed to the secondary phase La3Ni13B2, which improves the electrochemical activity of electrode surface, as well as to the phase boundary in multiphase structure, which decreases the lattice distortion and strain energy and enhances the anti-pulverization property of the alloy electrodes.Highlights► Commercial Fe–B alloy has lower cost than Cu, pure Fe and B, and lower melt point than pure Fe and B. ► Alloys consist of LaNi5 phase and La3Ni13B2 phase, and La3Ni13B2 phase increases with increasing x. ► The alloy with x = 0.10 exhibits the best high-rate dischargeability. ► Cycling stability of alloy electrodes increases with increasing x value. ► The improvement of HRD and cycling stability is ascribed to La3Ni13B2 phase and phase boundary.

The effect of Cal0.5W0.5 (CAW) compound on the grain refinement of Mg-Al based alloys was investigated. The results show that CAW compound is an effective and active grain refiner. The grain size of binary Mg-Al alloys is more than 500 μm, and it is changed to about 110 μm with a 1 wt.% CAW addition. The hardness increased with the decease of grain size monotonously. The mechanical properties are improved by the addition. The fine grain size is mainly ascribed to the dispersed Al2CO particles, which are very potent nucleating substrates for Mg-Al alloys. The nucleation cores formed by chemical reaction directly are well-distributed in the matrix.

Ti45Zr35Ni20−xPdx (x = 0, 1, 3, 5 and 7, at%) alloys were prepared by melt-spinning. The phase structure and electrochemical hydrogen storage performances of melt-spun alloys were investigated. The melt-spun alloys were icosahedral quasicrystalline phase, and the quasi-lattice constant increased with increasing x value. The maximum discharge capacity of alloy electrodes increased from 79 mAh/g (x = 0) to 148 mAh/g (x = 7). High-rate dischargeability and cycling stability were also enhanced with the increase of Pd content. The improvement in the electrochemical hydrogen storage characteristics may be ascribed to better electrochemical activity and oxidation resistance of Pd than that of Ni.

Ti45Zr35Ni13Pd7 alloys are prepared by melt spinning at different cooling rates (v). The phase structure and electrochemical hydrogen storage performance are investigated. When v is 10 m/s, the alloy consists of icosahedral quasicrystalline phase (I-phase), C14 Laves phase and a little amorphous phase. When v increases to 20 or 30 m/s, a mixed structure of I-phase and amorphous phase is formed. Maximum discharge capacity of alloy electrode decreases from 156 mAh/g (v = 10 m/s) to 139 mAh/g (v = 30 m/s) with increasing v. High-rate dischargeability at the discharge current density of 240 mA/g decreases monotonically from 61.2% (v = 10 m/s) to 56.8% (v = 30 m/s). Cycling retention rate S20 increases from 62.2% (v = 10 m/s) to 66.1% (v = 30 m/s) with increasing v, which is ascribed to the increase in amorphous phase.

Ti45Zr30Ni25Yx (x = 1, 3, 5 and 7) alloys were prepared by melt-spinning at wheel velocity of 20 m s−1. The effect of additive Y on phase structure and electrochemical performance of melt-spun alloys was investigated. Ti45Zr30Ni25Yx melt-spun alloys were composed of I-phase and amorphous phase. The amorphous phase increased with increasing x value, indicating amorphous forming ability improved with increasing Y content. The maximum discharge capacity and high-rate dischargeability decreased with increasing x value, which may be ascribed to the decrease of nickel content. Cycling stability first increased with increasing x from 1 to 3, and then decreased when x increased to 7, which was resulted from the combined effect of the decrease of nickel content and the increase of amorphous phase.

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) alloys 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 lattice 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.

In this paper, we report a new Gd2Co7-type Sm1.6Mg0.4Ni7 compound as a hydrogen storage material with a special hydrogen absorption/desorption process and good hydrogen storage ability. The Gd2Co7-type Sm1.6Mg0.4Ni7 compound absorbs 1.88 wt% H2 within 17 min at 298 K under 10 MPa H2. Meanwhile, the hydrogen absorption speed accelerates to 3.4 min after 20 hydrogenation/dehydrogenation cycles with a 1.44 wt% H2 under 3 MPa H2. Especially, the capacity retention of the compound is 99.3% at the 100th cycle. We found the hydrogen absorption/desorption of the compound undergoes two equilibrium stages, relating to the transformation of H2 between H-solid solution phase and hydride phase with a lower rate and higher enthalpy change at the lower concentration H2 stage, and the direct conversion between H2 and the hydride phase with a higher rate and lower enthalpy change at the higher concentration H2 stage. The two step mode lowers the inner-molecular strain and mismatch in subunit volumes of the compound in hydrogen absorption/desorption, caused by the transformation of H2 at the lower concentration of H2 stage, thus leading to good structural stability and excellent cycling stability. The new insights are expected to provide viable intermetallic materials as high-pressure tank materials for hydrogen storage with nice hydrogen storage properties.