CaCu5-type Structure Research Articles

Microstructure and Electrochemical Properties of La<sub>0.7</sub>Mg<sub>0.3</sub>(Ni<sub>1-x</sub>Co<sub>x</sub>)<sub>3.5</sub>(x=0.0-0.2) Type Hydrogen Storage Alloy

La0.7Mg0.3(Ni1-xCox)3.5 (x=0.0-0.2) type hydrogen storage alloy was prepared. In order to optimizing the content of Co it was studied effects that Co replaced Ni on the structure and electrochemical properties of La0.7Mg0.3(Ni1-xCox)3.5(x=0.0-0.2) type hydrogen storage alloy X-ray diffraction (XRD) analyses showed that the alloys were composed of the LaNi5 phase with the CaCu5-type structure and the (La,Mg)2Ni7 phase with the Ce2Ni7-type structure. The maximum electrochemical discharge capacity increases with the increase of Co content. Moreover, the cycle stabilities of La0.7Mg0.3(Ni1-xCox)3.5 was improved remarkably by small quantity replacement Ni by Co, after 250 times, the discharge capacity was increased from 30% (x=0.0) to 65% (x=0.20).

Effect of high and low temperature on the electrochemical performance of LaNi4.4−Co0.3Mn0.3Al hydrogen storage alloys

Abstract Different electrochemical measurements such as activation and maximum capacity, cyclic stability, self-discharge property, high-rate dischargeability and electrochemical impedance spectroscopy have been carried out to investigate the electrochemical performances of LaNi 4.4− x Co 0.3 Mn 0.3 Al x hydrogen storage alloys at low and high temperatures. We have selected 273 K and 323 K as low and high temperatures respectively. Samples W, X, Y and Z were used to represent alloys LaNi 4.4 Co 0.3 Mn 0.3 , LaNi 4.3 Co 0.3 Mn 0.3 Al 0.1 , LaNi 4.2 Co 0.3 Mn 0.3 Al 0.2 and LaNi 4.1 Co 0.3 Mn 0.3 Al 0.3 . XRD patterns show the alloys are all single-phase alloys with hexagonal CaCu5 type structure. The highest maximum discharge capacity is 340.3 mA h/g for alloy X, which is higher than other alloys at same temperature and high temperature. After 50 charge/discharge cycles, capacity retention of 93.6% has been observed at low temperature for alloy Z. The least capacity loss was 13.3% at 273 K during the self-discharge test. At both studied temperatures, alloy Z has the highest high-rate dischargeability (HRD) of 56.6% and 44.9% respectively at a discharge current density of 1800 mA/g. The electrochemical impedance spectroscopy (EIS) analysis was carried out to determine the charge-transfer resistance ( R ct ) which was further used in the analysis of the HRD. Alloy Z with the highest HRD at 273 K has a lower R ct of 0.9272 mΩ due to the dissolution or presence of Al into the electrolyte which can effectively reduce the total resistance of alloys. Apparently, at the two different testing temperatures, all the alloys possess better electrochemical properties at 273 K than 323 K.

Synthesis and structural characterization of mechanically alloyed AB3-type based material: LaZr2Mn4Ni5

In this study, a new AB3-type compound LaZr2Mn4Ni5 has been synthesized by mechanical alloying (MA) process starting from a mixture of two binary compounds LaNi5 (CaCu5-type structure, P6/mmm space group) and ZrMn2-Laves phase (MgZn2-type structure, P63/mmc space group) in order to take advantage of the hydrogen absorption properties of these two types of intermetallic compounds. X-ray diffraction (XRD), electron probe micro-analysis (EPMA) and transmission electron microscopy (TEM) were used to determine the structural properties and the phase evolution of the powder mixtures for different milling durations ranging from 5 to 25 h. The results show multiphase alloys which contain LaZr2Mn4Ni5 main phase with hexagonal PuNi3-type structure (R-3m space group). Rietveld analysis proves that both of La and Zr atoms are located in the two types of allowed sites 3a and 6c of the PuNi3-type structure. It is found that using a planetary ball mill, the maximum weight content (40 wt%) of LaZr2Mn4Ni5 compound was obtained at room temperature after 5 h of mechanical alloying.

Phase structures and electrochemical properties of La0.8−xGd0.2MgxNi3.1Co0.3Al0.1 hydrogen storage alloys

La0.8−xGd0.2MgxNi3.1Co0.3Al0.1 (x = 0.1–0.5) hydrogen storage alloys are prepared by an induction melting followed by annealing treatment for 168 h at 1173 K in a sealed stainless steel tube. Instrumentation analyses indicate that the chemical composition and crystalline phase structure of these annealed alloys closely depended on the Mg content (x). At lower x than 0.25, the main phase is the Ce2Ni7-type phase and its phase abundance is 93.4 wt.%. When x > 0.2, the alloys are composed three phases, A2B7-type, CaCu5-type and PuNi3-type structure, in which phase abundance of the PuNi3- and CaCu5-type phase increases to 44.99 wt.% and 44.8 wt.% respectively. When Mg is controlled at x < 0.3, the volume of unit cell of Ce2Ni7-type decreases from 0.5391 nm3 to 0.5170 nm3. Hydrogen absorption capacity reaches maximum value (1.43 wt.%) at Mg = 0.15, whereas the absorption of hydrogen storage content decreases with the x increase, accordingly. Electrochemical measurements indicates La0.65Gd0.2Mg0.15Ni3.1Co0.3Al0.1 alloy electrode exhibits the maximum electrochemical discharge capacity of 391.4 mAh g−1 and the best cyclic stability S100 of 92.0%.

Effect of Al content on structure and electrochemical properties of LaNi4.4 − xCo0.3Mn0.3Alx hydrogen storage alloys

The structure and electrochemical properties of LaNi4.4 − xCo0.3Mn0.3Alx hydrogen storage alloys have been investigated by XRD and simulated battery test, including maximum capacity, cyclic stability, self-discharge, high-rate dischargeability (HRD). Samples A, B, C and D were used to represent alloys LaNi4.4Co0.3Mn0.3Al, LaNi4.3Co0.3Mn0.3Al0.1, LaNi4.2Co0.3Mn0.3Al0.2 and LaNi4.1Co0.3Mn0.3Al0.3 respectively. The results indicated that as-prepared LaNi4.4 − xCo0.3Mn0.3Alx alloys are all single-phase alloys with hexagonal CaCu5 type structure. The maximum discharge capacity is 330.4 mAh g−1 (Alloy C). With the increase of Al content from A to D, cycle life of alloy electrode has been improved. Higher capacity retention of 89.29% (after 50 charge/discharge cycles) has been observed for electrode D, while with a smaller capacity loss of 12.5% in its self-discharge test. Better high-rate charge/discharge behaviors have been observed in electrode B, and the maximum data is 54.7% at charge current of 900 mA/g) and 68.54% at discharge current of 1800 mA/g). Furthermore, the electrochemical impedance spectroscopy (EIS) analysis shown that the reaction of alloy electrode is controlled by charge-transfer step. The addition of Al results in the formation of protective layer of aluminum oxides on the surface of the alloy electrode, which is good for the improvement of electrode properties in alkaline solution and is detrimental for the charge-transfer process. Therefore, a suitable addition of Al is needed to improve its electrode properties.

Magnetic, transport and electronic properties of SmNi4Si compound

The polycrystalline sample of SmNi4Si was investigated by means of powder X-ray diffraction, magnetic susceptibility, magnetization, electrical resistivity and specific heat measurements. This compound crystallizes in the hexagonal CaCu5-type structure (space group P6/mmm) and orders magnetically at TC = 14.9 K. The magnetization, electrical resistivity and specific heat data indicate that the electronic ground state of the SmNi4Si has a ferromagnetic-like character. The magnitude of energy gap in the magnon spectrum calculated from electrical resistivity data revealed the presence of high influence of magnetocrystalline anisotropy effect. Our experimental studies were supported by first-principles calculations employing DFT method together with LSDA + U approach. We explore implication of U parameter for magnetization of SmNi4Si. Obtained theoretical result shows that the electronic structure and magnetic properties of SmNi4Si for U = 6 eV is closer to our experimental results.

Electrochemical hydrogen storage characteristics of as-cast and annealed La0.8-xNdxMg0.2Ni3.15Co0.2Al0.1Si0.05 (x=0–0.4) alloys

The La-Mg–Ni–based A2B7-type La0.8-xNdxMg0.2Ni3.15Co0.2Al0.15 (x=0, 0.1, 0.2, 0.3, 0.4) electrode alloys were prepared by casting and annealing. The influences of partial substitution of Nd for La on the structure and electrochemical performance of the as-cast and annealed alloys were investigated. It was found that the experimental alloys consist of two major phases, (La, Mg)2Ni7 phase with the hexagonal Ce2Ni7-type structure and LaNi5 phase with the hexagonal CaCu5-type structure, as well as some residual phase LaNi3 and NdNi5. The discharge capacity and high rate discharge ability (HRD) of the as-cast and annealed alloys first increase and then decrease with Nd content growing. The as-cast and annealed alloys (x=0.3) yield the largest discharge capacities of 380.3 and 384.3 mA·h/g, respectively. The electrochemical cycle stability of the as-cast and annealed alloys markedly grows with Nd content rising. As the Nd content increase from 0 to 0.4. The capacity retaining rate (S100) at the 100th charging and discharging cycle increases from 64.98% to 85.17% for the as-cast alloy, and from 76.60% to 96.84% for the as-annealed alloy.

Structure and electrochemical hydrogen storage characteristics of La0.8−x Pr x Mg0.2Ni3.15Co0.2Al0.1Si0.05 (x=0–0.4) electrode alloys

For the purpose of improving the electrochemical cycle stability of the La-Mg-Ni based A2B7-type electrode alloys, both reducing Mg content and substituting La with Pr were adopted. The La0.8−xPrxMg0.2Ni3.15Co0.2Al0.1Si0.05 (x=0, 0.1, 0.2, 0.3, 0.4) electrode alloys were fabricated by casting and annealing. The investigation on the structures and electrochemical performances of the alloys was performed. The obtained results reveal that the as-cast and annealed alloys comprise two major phases, (La, Mg)2Ni7 phase with the hexagonal Ce2Ni7-type structure and LaNi5 phase with the hexagonal CaCu5-type structure, as well as a little residual LaNi3 phase. It is also found that the addition of Pr element observably affects the electrochemical hydrogen storage characteristics of the alloys, just as the discharge capacity and high rate discharge ability (HRD) first rise then fall with the growing of Pr content, and among all the alloys, the as-cast and annealed (x=0.3) alloys generate the largest discharge capacities of 360.8 and 386.5 mA·h/g, respectively. Additionally, the electrochemical cycle stability of all the alloys markedly grows with the increase of Pr content. The capacity retaining rate (S100) at the 100th charging and discharging cycle is enhanced from 64.98% to 77.55% for the as-cast alloy, and from 76.60% to 95.72% for the as-annealed alloy by rising Pr content from 0 to 0.4. Furthermore, the substitution of Pr for La results in first increase and then decrease in the hydrogen diffusion coefficient (D), the limiting current density (IL) as well as the electrochemical impedance.

Electrochemical performances of as-cast and annealed La0.8-x Nd x Mg0.2Ni3.35Al0.1Si0.05 (x = 0–0.4) alloys applied to Ni/metal hydride (MH) battery

The La–Mg–Ni-based A2B7-type La0.8-x Nd x Mg0.2Ni3.35Al0.1Si0.05 (x = 0, 0.1, 0.2, 0.3, and 0.4) electrode alloys were prepared by casting and annealing. The influence of the partial substitution of Nd for La on the structure and electrochemical performances of the alloys was investigated. The structural analysis of X-ray diffraction and scanning electron microscopy reveals that the experimental alloys consist of two major phases: (La,Mg)2Ni7 with the hexagonal Ce2Ni7-type structure and LaNi5 with the hexagonal CaCu5-type structure as well as some residual phases of LaNi3 and NdNi5. The electrochemical measurements indicate that an evident change of the electrochemical performance of the alloys is associated with the substitution of Nd for La. The discharge capacity of the alloy first increases then decreases with the growing Nd content, whereas their cycle stability clearly grows all the time. Furthermore, the measurements of the high rate discharge ability, the limiting current density, and hydrogen diffusion coefficient all demonstrate that the electrochemical kinetic properties of the alloy electrodes first augment then decline with the rising amount of Nd substitution.

Coercivity behavior in [formula omitted] system as function of the microstructureevolution

Magnetic measurements, X-ray diffraction and scanning electron microscopy (SEM) experiments were carried out in the as-cast Gd(Co1−xCux)5 samples with different Co/Cu content. Already in the as cast state, this system shows high coercive field for x=0.3 and a magnetization driven by nucleation of reversal domain. SEM micrograph and microanalysis show possible spinodal decomposition in the as-cast state, hence regions with different Co/Cu-content are observed, while the Gd-content almost does not change. High resolution X-ray diffraction patterns show a main CaCu5-type structure with traces of a secondary phase and distorted peak profiles as function of the Cu content. The evolution of the microstructure is discussed in relation with the Cu incorporation into the CaCu5-type structure. The Cu addition avoids the formation of the 2:7 phase within the 1:5 matrix, favoring the formation of a more homogeneous Gd(Co,Cu)5 phase. The relation between the observed microstructure and the magnetic behavior is also discussed.

Gd Substitution Effects on the Magnetic Properties of the Pr1−x Gd x Co4Si Compounds

The crystal structure and magnetic properties of single phase Pr1−xGdxCo4Si compounds with x=0,0.2,0.4,0.6,0.8, and 1.0 have been investigated. X-ray analysis reveals that the compounds crystallize as a single phase having the hexagonal CaCu5-type structure with the space group P6/mmm. The substitution of Gd for Pr causes a linear decrease of the unit-cell parameters a and c, and the unit-cell volume V. Magnetic measurements indicate that all samples are ordered magnetically below the Curie temperature. The saturation magnetization at 4.2 K decreases upon the Gd substitution up to x=0.6, and then increases.

Study on the microstructure and electrochemical kinetic properties of MmNi4.50−xMnxCo0.45Al0.30 (0.25≤x≤0.45) hydrogen storage alloys

Abstract The phase structures, surface morphologies and electrochemical kinetic properties of MmNi4.50−xMnxCo0.45Al0.30 (Mm is the mischmetal, x = 0.25, 0.30, 0.35, 0.40 and 0.45) hydrogen storage alloys have been investigated in this paper. The X-ray diffraction (XRD) shows that all the alloys mainly consist of LaNi5 phase with CaCu5-type structure, which belongs to P6/mmm space group (central symmetry). Scanning electron microscopy (SEM) tests indicate that there are partial element segregations in the alloys. Meanwhile, energy dispersive spectrum (EDS) results display that the elements constituting Mm exist in the matrix phase in relatively larger proportion, while Mn, Al and Co tend to appear in precipitate phase. For the alloy with x = 0.35, the electrochemical performances, including discharge capacity, high-rate dischargeability (HRD) and cycling life, of the alloy electrode are better than that of other alloy electrodes. With the increase of Mn content, the exchange current density (I0) of the alloy electrodes first increases and then decreases, the hydrogen diffusion coefficient (D) of alloy electrodes gradually decreases. There is a linear correlation between HRD at a discharge current density of 1500 mA/g and I0.

Effect of Co substitution for Ni on the microstructure and electrochemical properties of La-R-Mg-Ni-based hydrogen storage alloys

Hydrogen storage alloys La0.63Gd0.2 Mg0.17Ni3.35−x Co x Al0.15 (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 electrochemical properties of La0.63Gd0.2 Mg0.17Ni3.35−x Co x Al0.15 (x = 0, 0.1, 0.3, 0.5, 1.0, 1.5, 2.0) alloy electrodes depended on the alloy structure type. XRD patterns and EPMA showed that the alloys consisted of Ce2Ni7-type (Gd2Co7-type), CaCu5-type, Pr5Co19-type, and PuNi3-type phase structure. Pr5Co19-type and Ce2Ni7-type phase increased with the increase of Co content x. However, CaCu5-type phase firstly decreased then increased as Co content increased. 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 and then decreased. The La0.63Gd0.2 Mg0.17Ni3.05Co0.3Al0.15 alloy electrode exhibited the maximum discharge capacity (392.92 mAh/g), and La0.63Gd0.2 Mg0.17Ni1.85Co1.5Al0.15 alloy electrode showed the best cyclic stability (S100 = 96.1 %). The electrochemical kinetics studies indicate that La0.63Gd0.2 Mg0.17Ni1.85Co1.5Al0.15 exhibited a higher rate dischargeability (HRD900 = 86.3 %). Electrochemical analyses showed that the control process of alloy electrode reaction is charge-transfer rate in surface film of alloy.

Magnetic and transport properties of selected YbxGd1−xNi5 intermetallics

We report the magnetic and transport properties of the YbxGd1−xNi5 (x ≤ 0.5) intermetallic compounds. According to the X-ray diffraction (XRD) this series crystallize in the hexagonal CaCu5-type structure. The magnetic properties in the studied system strongly depends on Yb concentration. Moreover, the so-called field cooled–zero field cooled (FC–ZFC) curves reveal an unexpected existence of a negative magnetization M in a certain temperature range. The M(T) dependences exhibit two compensation points in which the value of M equals zero. The origin of the observed behaviour may be due to the possible switching effect in spin (M4fS) and orbital (M4fL) moment within 4f sublattice. Near the compensation points where the opposing contribution from 4f local magnetic moments are nearly equals the conduction electron polarization become significant. Additionally, the observed exchange bias in the vicinity of the compensation point can be attributed to the anisotropy between the coupling within spin (M4fS) and orbital (M4fL) moments. The observed unique behaviour is the most evident in the case of x = 0.4 ytterbium concentration. The transport properties confirm the results obtained by the magnetic studies.

A thermodynamic re-modeling of the Co-Fe-Gd system

The Fe-Gd and Co-Fe-Gd systems were optimized by means of the CALPHAD (CALculation of PHAse Diagram) technique. The solution phases, liquid, bcc, fcc and hcp, were described by the substitutional solution model. For the Fe-Gd system, the compounds Fe23Gd6, Fe3Gd and Fe2Gd with no solubility ranges were treated as stoichiometric compounds. According to the CaCu5-type structure of the intermetallic compounds Fe17Gd2, it was reasonable to adopt a three-sulattice model (Fe2,Gd)Gd2Fe15 in the Fe-Gd system, and this model was also adopted as (Co2,Fe2,Gd)(Co2,Gd)2 (Co,Fe)15 to describe the compounds (Co,Fe)17Gd2 and (Co,Fe)5Gd in the Co-Fe-Gd ternary system. The other compounds were treated as the line compounds (Co,Fe)mGdn and no ternary compound had been reported in the Co-Fe-Gd system. The thermodynamic description of the Co-Fe and Co-Gd system were taken from literatures. A self-consistent thermodynamic description of the Co-Fe-Gd system was obtained.

Microstructures and electrochemical characteristics of La0.7Ce0.3Ni3.75−xCu0.75Mn0.35Al0.15(V0.81Fe0.19)x (x = 0–0.20) hydrogen storage alloys

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 320mAh/g (x=0) to 299mAh/g (x=0.20). The high-rate dischargeability at the discharge current density of 1200mA/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.

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 La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75x(V0.81Fe0.19)x hydrogen storage alloys were investigated. XRD indicated that La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75x(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.

Structure and electrochemical hydrogen storage characteristics of the as-cast and annealed La0.8-xSmxMg0.2Ni3.15Co0.2Al0.1Si0.05 (x=0-0.4) alloys

In order to ameliorate the electrochemical cycle stability of the RE-Mg-Ni based A2B7-type electrode alloys, the Mg content in the alloy was reduced and La in the alloy was partially substituted by Sm. The La0.8-xSmxMg0.2Ni3.15Co0.2Al0.1Si0.05 (x=0, 0.1, 0.2, 0.3, 0.4) electrode alloys were fabricated by casting and annealing. The microstructures of the as-cast and annealed alloys were characterized by XRD and SEM. The electrochemical hydrogen storage characteristics of the as-cast and annealed alloys were measured. The results revealed that all of the experimental alloys mainly consisted of two phases: (La, Mg)2Ni7 phase with the hexagonal Ce2Ni7-type structure and LaNi5 phase with the hexagonal CaCu5-type structure. As Sm content grew from 0 to 0.4, the discharge capacity and the high rate discharge ability (HRD) first increased and then decreased for the as-cast and annealed alloys, whereas the capacity retaining rate (S100) after 100 cycles increased continuously.

An investigation on electrochemical hydrogen storage performances of the as-cast and -annealed La0.8−xSmxMg0.2Ni3.35Al0.1Si0.05 (x = 0–0.4) alloys

The as-cast and -annealed La–Mg–Ni-based A2B7-type La0.8−xSmxMg0.2Ni3.35Al0.1Si0.05 (x=0, 0.1, 0.2, 0.3, 0.4) electrode alloys were prepared, and the influences of the partial substitution of Sm for La on the structure and electrochemical performances of the alloys were investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM) and electrochemical measurements. The results indicate that all the experimental alloys mainly consist of two phases, (La, Mg)2Ni7 phase with the hexagonal Ce2Ni7-type structure and LaNi5 phase with the hexagonal CaCu5-type structure. The substitution of Sm for La gives rise to an obvious change in the electrochemical performances of the alloys. The discharge capacity of the as-cast and -annealed alloys first increases and then decreases with the growing of Sm content, whereas the cycle stability of the as-cast and -annealed alloys always increases with the rising of Sm content. Furthermore, the high rate discharge ability (HRD), the electrochemical impedance spectrum (EIS), Tafel polarization curves and potential-step measurements all indicate that the electrochemical kinetic properties of the alloy electrodes first increase then decrease with the rising amount of Sm substitution.

Composition optimization and electrochemical characteristics of Co-free Fe-containing AB5-type hydrogen storage alloys through uniform design

In order to reduce the cost of AB5-type hydrogen storage alloys, effects of substitution of Ce for La (A side) and Fe, Mn, Al for Ni (B side) on structural and electrochemical properties of (LaCe)1(NiFeMnAl)5 alloys were studied systematically. To make component uniform and operation easy, uniform design (UD) method was introduced into the study of composition optimization of Co-free Fe-containing AB5-type alloys for the first time. X-ray diffraction (XRD) results showed that the designed alloys were of single CaCu5-type structure phase. The replacement of Fe had a severe effect on electrochemical capacity, and the substitution of Fe and Al had a synergetic action among the unit cell volume, cycling stability and high rate discharge property. Interestingly, it was found that the hydrogen storage alloys with excessively high plateau pressure showed a tilted line in Nyquist plot instead of the semicircle, and the current decayed rapidly to near zero at the beginning of the step in constant potential step (CPS), indicating that electrochemical impedance spectra (EIS) and CPS cannot accurately measure the electrochemical kinetics process of the hydrogen storage alloys with excessively high plateau pressure.