Electrochemical Hydrogen Storage Performances Research Articles

Electrochemical hydrogen storage characteristics of La0.75−x M x Mg0.25Ni3.2Co0.2Al0.1 (M = Zr, Pr; x = 0, 0.1) alloys prepared by melt spinning

In order to ameliorate the electrochemical hydrogen storage performances of La-Mg-Ni system A2B7-type electrode alloys, the partial substitution of M (M = Zr, Pr) for La was performed. The melt spinning technology was used to fabricate the La0.75−xMxMg0.25Ni3.2Co0.2Al0.1 (M = Zr, Pr; x = 0, 0.1) electrode alloys. The influences of the melt spinning and substituting La with M (M = Zr, Pr) on the structures and the electrochemical hydrogen storage characteristics of the alloys were investigated. The analysis of XRD, SEM, and TEM reveals that the as-cast and spun alloys have a multiphase structure composed of two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The as-spun (M = Pr) alloy displays an entire nanocrystalline structure, while an amorphous-like structure is detected in the as-spun (M = Zr) alloy, implying that the substitution of Zr for La facilitates the amorphous formation. The electrochemical measurements exhibit that the substitution of Pr for La clearly increases the discharge capacity of the alloys; however, the Zr substitution brings on an adverse impact. Meanwhile, the M (M = Zr, Pr) substitution significantly enhances its cycle stability. The melt spinning exerts an evident effect on the electrochemical performances of the alloys, whose discharge capacity and high rate discharge ability (HRD) first mount up and then fall with the growing spinning rate, whereas their cycle stabilities monotonously augment as the spinning rate increases.

Electrochemical performances of the as-melt La0.75−xMxMg0.25Ni3.2Co0.2Al0.1 (M = Pr, Zr; x = 0, 0.2) alloys applied to Ni/metal hydride (MH) battery

The partial replacement of La by M (M = Pr, Zr) has been performed in order to ameliorate the electrochemical hydrogen storage performances of La–Mg–Ni-based A2B7-type electrode alloys. For this purpose, we adopt melt spinning technology to prepare the La0.75−xMxMg0.25Ni3.2Co0.2Al0.1 (M = Pr, Zr; x = 0, 0.2) electrode alloys. Then systemically investigate the effects that the preparation methods and M (M = Pr, Zr) substitution have on the structures and electrochemical hydrogen storage characteristics of the alloys. The analysis of XRD and TEM reveals that the as-cast and spun alloys hold a multiphase structure, containing two main phases (La, Mg)2Ni7 and LaNi5 as well as a trace of residual phase LaNi2. Besides, the as-spun (M = Pr) alloy displays an entire crystalline structure, while an amorphous-like structure is detected in the as-spun (M = Zr) alloy, implying the replacement of La by Zr facilitates forming amorphous phase. Based upon electrochemical measurements, an impact engendered by melt spinning on the electrochemical performances of the alloys appears to be evident. The cycle stabilities monotonously augment with the growing of the spinning rate. The discharge capacity and high rate discharge ability (HRD), however, exhibit difference. For the (M = Pr) alloy, they first mount up and then fall with the rising of the spinning rate, whereas for the (M = Zr) alloy, they always decline as the spinning rate elevates. Furthermore, the replacement of La by M (M = Pr, Zr) considerably enhances the cycle stability of the alloys and the replacement of La by Pr clearly increases the discharge capacity, but the Zr replacement results in an adverse impact.

Influence of Substituting La with Zr on Electrochemical Characteristics of As-Spun RE–Mg–Ni-Based A<sub>2</sub>B<sub>7</sub>-Type Alloys

In order to ameriolate the electrochemical hydrogen storage performances of La–Mg–Ni system A2B7-type electrode alloys, the partial substitution of Zr for La has been performed. The La0.75−xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) electrode alloys were prepared by melt spinning. The influences of substithting La with Zr on the structures and the electrochemical hydrogen storage characteristics of the alloys were investigated. The structure characterized by XRD and TEM displays that the as-spun alloys have a multiphase structure, composing of two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The as-spun Zr-free alloy displays an entire nanocrystalline structure, while an like amorphous structure is detected in the as-spun alloy substituted by Zr, implying that the substitution of Zr for La facilitates the amorphous formation. The substitution of Zr for La markedly enhances the electrochemical cycle stability of the alloys, whereas the impact generated by such substitution on the high rate discharge ability (HRD) of the alloys is different with the variation of the spinning rate. The HRD of the as-spun (5 m/s) alloys yields the largest value with the change of Zr content, but that of the as-spun (20 m/s) alloys always declines with the growing amount of Zr substitution.

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.

Macroporous ZnO Nanofilms and its Electrochemical Hydrogen Storage Ability

Macroporous ZnO nanofilms were synthesized by a simple hydrothermal reaction. The products exhibit noticable hydrogen storage capacity and big BET surface area. The present work shows that the nanostructures of products are important to their electrochemical hydrogen storage performances. On the other hand, the low cost, convenient process, good reproducibility, high yield, and clean reactions of the present synthetic method make it possible to scale it up to industrial production.

Macroporous ZnO Nanofilms and its Electrochemical Hydrogen Storage Ability

Macroporous ZnO nanofilms were synthesized by a simple hydrothermal reaction. The products exhibit noticable hydrogen storage capacity and big BET surface area. The present work shows that the nanostructures of products are important to their electrochemical hydrogen storage performances. On the other hand, the low cost, convenient process, good reproducibility, high yield, and clean reactions of the present synthetic method make it possible to scale it up to industrial production.

Impacts of Melt Spinning and Element Substitution on Electrochemical Characteristics of the La–Mg–Ni-based A<sub>2</sub>B<sub>7</sub>-Type Alloys

The partial substitution of Zr for La has been performed in order to ameliorate the electrochemical hydrogen storage performances of La–Mg–Ni based A2B7-type electrode alloys. The melt spinning technology was used to prepare the La0.75-xZrxMg0.25Ni3.2Co0.2Al0.1 (x=0, 0.05, 0.1, 0.15, 0.2) electrode alloys. The impacts of the melt spinning and the substituting La with Zr on the structures and the electrochemical hydrogen storage characteristics of the alloys were systemically investigated. The analysis of XRD and TEM reveals that the as-cast and spun alloys have a multiphase structure, composing of two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The electrochemical measurement indicates that both the substitution of Zr for La and the melt spinning ameliorate the electrochemical cycle stability of the alloys dramatically. Furthermore, the high rate discharge ability (HRD) of the as-spun (10 m/s) alloys notably declines with growing the amount of Zr substitution, while it first augments and then falls for the (x=0.1) alloy with rising the spinning rate.

Influences of melt spinning on electrochemical hydrogen storage performance of nanocrystalline and amorphous Mg2Ni-type alloys

In order to improve the electrochemical hydrogen storage performance of the Mg2Ni-type electrode alloys, Mg in the alloy was partially substituted by La, and the nanocrystalline and amorphous Mg2Ni-type Mg20−xLaxNi10 (x=0, 2) alloys were synthesized by melt-spinning technique. The microstructures of the as-spun alloys were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical hydrogen storage properties of the experimental alloys were tested. The results show that no amorphous phase is detected in the as-spun Mg20Ni10 alloy, but the as-spun Mg18La2Ni10 alloy holds a major amorphous phase. As La content increases from 0 to 2, the maximum discharge capacity of the as-spun (20 m/s) alloys rises from 96.5 to 387.1 mA·h/g, and the capacity retaining rate (S20) at the 20th cycle grows from 31.3% to 71.7%. Melt-spinning engenders an impactful effect on the electrochemical hydrogen storage performances of the alloys. With the increase in the spinning rate from 0 to 30 m/s, the maximum discharge capacity increases from 30.3 to 135.5 mA·h/g for the Mg20Ni10 alloy, and from 197.2 to 406.5 mA·h/g for the Mg18La2Ni10 alloy. The capacity retaining rate (S20) of the Mg20Ni10 alloy at the 20th cycle slightly falls from 36.7% to 27.1%, but it markedly mounts up from 37.3% to 78.3% for the Mg18La2Ni10 alloy.

Electrochemical hydrogen storage performance of Mg 2− xAl xNi thin films

Mg 2− x Al x Ni thin films ( x = 0, 0.1, 0.2, 0.3) are prepared by magnetron sputtering. Their charge–discharge properties are tested, and the effects of Al partial substitution for Mg on the change of the enthalpy of hydrides formation and electrochemical properties are discussed. The charge–discharge experiments show that the discharge properties of the Mg 2Ni film are improved by the substitution of Al for Mg. The change of the enthalpy of hydrides formation of the Mg 2− x Al x Ni film decrease with the increase of Al content, which indicate that the stability of the Mg 2− x Al x Ni film hydrides decrease with the increase of Al content. The potentiodynamic polarization results show that the anti-corrosion property of Mg 2Ni thin film is improved with the partial substitution of Al for Mg. Electrochemical impedance spectra studies suggest that the oxide layer thickness decrease with Al substitution, and the charge-transfer resistance of the film electrode increase from 202 Ω (Mg 2Ni) to 1474 Ω (Mg 1.6Al 0.4Ni) which indicates that the reaction rate at the electrode surface decrease.

Improvement of the electrochemical hydrogen storage performance of magnesium based alloys by various additive elements

Mg1.5Ti0.3Zr0.1M0.1Ni (M = Al, B, C, Fe, Pd) type alloys were synthesized by mechanical alloying and their electrochemical hydrogen storage characteristics were investigated. While Al deteriorated the alloy initial discharge capacity, it improved the alloy cyclic stability. The reversibility in the presence of B was very poor. Addition of B increased the alloy initial discharge capacity but reduced the alloy capacity retention rate. The cyclic stability of Fe-including alloy was much better than that of C-including alloy, although both of them have almost the same initial discharge capacities. Both the alloy initial discharge capacity and the alloy cyclic stability were improved significantly in the presence of Pd. The analysis by the electrochemical impedance spectroscopy revealed that Fe increased the corrosion resistance of the alloy without degrading the capacity retention rate. The hydroxide barrier layer in the presence of Al was predicted to be more porous due to the possible high rate selective dissolution of the disseminated Al-oxides.

Enhanced Electrochemical Hydrogen Storage Characteristics of Nanocrystalline and Amorphous Mg20Ni10-xCox (x=0-4) Alloys by Melt Spinning

Abstract In order to improve the electrochemical hydrogen storage performances of the Mg 2 Ni-type alloys, Ni in the alloy was partially substituted by element Co. The nanocrystalline and amorphous Mg 20 Ni 10- x Co x ( x =0, 1, 2, 3, 4) alloys were prepared by melt-spinning technology. The structures of the as-cast and spun alloys were studied by XRD, SEM and HRTEM. The electrochemical hydrogen storage characteristics of the alloys were measured. The results show that the substitution of Co for Ni leads to the formation of secondary phase MgCo 2 without altering the major phase of Mg 2 Ni. No amorphous phase is detected in the as-spun alloy ( x =0), whereas the as-spun alloy ( x =4) holds a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni significantly increases the glass forming ability of the Mg 2 Ni-type alloy. The substitution of Co for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, including the discharge capacity and the cycle stability, for which the increased glass forming ability by Co substitution is mainly responsible.

Electrochemical hydrogen storage characteristics of nanocrystalline and amorphous Mg 2Ni-type alloys prepared by melt-spinning

The nanocrystalline and amorphous Mg 2Ni-type alloys with nominal compositions of Mg 2Ni 1- x Mn x ( x=0, 0.1, 0.2, 0.3, 0.4) were synthesized by melt-spinning technique. The spun alloy ribbons with a continuous length, a thickness of about 30 μm and a width of about 25 mm are obtained. The structures of the as-spun alloy ribbons were characterized by XRD and HRTEM. The electrochemical hydrogen storage characteristics of the as-spun alloy ribbons were measured by an automatic galvanostatic system. The electrochemical impedance spectrums (EIS) were plotted by an electrochemical workstation. The hydrogen diffusion coefficients ( D) in the alloys were calculated by virtue of potential-step measurement. The results show that all the as-spun ( x=0) alloys hold a typical nanocrystalline structure, whereas the as-spun ( x=0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni facilitates the glass formation in the Mg 2Ni-type alloy. The substitution of Mn for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, involving the discharge capacity and the electrochemical cycle stability. With an increase in the amount of Mn substitution from 0 to 0.4, the discharge capacity of the as-spun (20 m/s) alloy increases from 96.5 to 265.3 mA·h/g, and its capacity retaining rate ( S 20) at the 20th cycle increases from 31.3% to 70.2%. Furthermore, the high rate dischargeability (HRD), electrochemical impedance spectrum and potential-step measurements all indicate that the electrochemical kinetics of the alloy electrodes first increases then decreases with raising the amount of Mn substitution.

Ultrasonochemical-Assisted Synthesis of CuO Nanorods with High Hydrogen Storage Ability

Uniform CuO nanorods with different size have been synthesized in a water-alcohol solution through a fast and facile ultrasound irradiation assistant route. Especially, the as-prepared CuO nanorods have shown a strong size-induced enhancement of electrochemical hydrogen storage performance and exhibit a notable hydrogen storage capacity and big BET surface area. These results further implied that the as-prepared CuO nanorods could be a promising candidate for electrochemical hydrogen storage applications. The observation of the comparison experiments with different concentrations of NaOH, ethanol, CTAB, and HTMA while keeping other synthetic parameters unchanged leads to the morphology and size change of CuO products.

Gaseous and Electrochemical Hydrogen Storage Properties of Nanocrystalline Mg<sub>2</sub>Ni-Type Alloys Prepared by Melt Spinning

A partial substitution of Ni by Cu has been carried out in order to improve the hydrogen storage characteristics of the Mg2Ni-type alloys. The nanocrystalline Mg20Ni10-xCux (x = 0, 1, 2, 3, 4) alloys are synthesized by the melt-spinning technique. The structures of the as-cast and spun alloys have been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM). The electrochemical performances were evaluated by an automatic galvanostatic system. The hydrogen absorption and desorption kinetics of the alloys were determined by using an automatically controlled Sieverts apparatus. The results indicate that the substitution of Cu for Ni does not alter the major phase Mg2Ni. The Cu substitution significantly ameliorates the electrochemical hydrogen storage performances of alloys, involving both the discharge capacity and the cycle stability. The hydrogen absorption capacity of alloys has been observed to be first increase and then decrease with an increase in the Cu contents. However, the hydrogen desorption capacity of the alloys exhibit a monotonous growth with an increase in the Cu contents.

Effect of Al, B, Ti and Zr additive elements on the electrochemical hydrogen storage performance of MgNi alloy

MgNi, Mg 0.9(M) 0.1Ni and Mg 0.8(M) 0.2Ni (M = Al, B, Ti, Zr) type alloys were synthesized by mechanical alloying and their electrochemical hydrogen storage characteristics were investigated. X-ray diffraction studies showed that although 15 h milling was enough to obtain amorphous/nano-crystalline MgNi alloy structure, the dissolution of all Ni in the main phase required at least 25 h milling. The discharge capacities of alloys were observed to increase sharply up to 15 h milling. Further increase up to 25 h did not cause change in the discharge capacities considerably. Titanium improved MgNi alloy discharge performance significantly. Although Al deteriorated the initial discharge capacity of MgNi alloy, it improved the alloy capacity retention rate. Despite the absence of any positive effect of B, Zr had limited positive effect on the alloy cyclic stability. It was estimated that up to 80% discharge level there was no considerable degradation by the anodic reaction in MgNi alloy since uncharged MgNi alloy stayed in the cathodic regime.

Improved hydrogen storage behaviours of nanocrystalline and amorphous Mg 2Ni-type alloy by Mn substitution for Ni

The nanocrystalline and amorphous Mg 2Ni-type alloys with nominal compositions of Mg 2Ni 1−xMn x ( x = 0, 0.1, 0.2, 0.3, 0.4) were synthesized by melt spinning technique. The structures of the as-cast and spun alloys were characterized by XRD, SEM and HRTEM. The hydrogen absorption and desorption kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system. The results show that the as-spun ( x = 0) alloy holds a typical nanocrystalline structure, whereas the as-spun ( x = 0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni facilitates the glass formation in the Mg 2Ni-type alloy. The hydrogen absorption capacity of the alloys first increases then decreases with rising Mn content, but the hydrogen desorption capacity of the alloys grows with increasing Mn content. Furthermore, the substitution of Mn for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, involving both the discharge capacity and the electrochemical cycle stability. With an increase in the amount of Mn from 0 to 0.4, the discharge capacity of as-spun (30 m/s) alloy grows from 116.7 to 311.5 mAh/g, and its capacity retaining rate at 20th charging and discharging cycle rises from 36.7 to 78.7%.

Microstructure and hydrogen storage characteristics of melt-spun nanocrystalline Mg 20Ni 10− xCu x ( x = 0–4) alloys

The nanocrystalline Mg 2Ni-type alloys with nominal compositions of Mg 20Ni 10− x Cu x ( x = 0–4) are synthesized by melt-spinning technique. The microstructures of the as-cast and spun alloys are characterized by XRD, SEM and HRTEM. The hydrogen absorption and desorption kinetics of the alloys are measured using an automatically controlled Sieverts apparatus. The electrochemical performances are tested by an automatic galvanostatic system. The results show that all the as-spun alloys hold typical nanocrystalline structure. The substitution of Cu for Ni does not change the major phase Mg 2Ni. The hydrogen absorption capacity of the alloys first increases and then decreases with rising Cu content, but the hydrogen desorption capacity of the alloys always grows with increasing Cu content. Furthermore, the substitution of Cu for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, involving both the discharge capacity and the electrochemical cycle stability.

Investigation on electrochemical performances of melt-spun nanocrystalline and amorphous Mg 2Ni 1− xMn x ( x = 0–0.4) electrode alloys

In order to enhance the glass forming ability of the Mn 2Ni-type electrode alloy, Ni in the Mg 2Ni compound is partially substituted by Mn. The nanocrystalline and amorphous Mg 2Ni-type alloys with nominal compositions of Mg 2Ni 1− x Mn x ( x = 0, 0.1, 0.2, 0.3, 0.4) are fabricated by melt-spinning technique. The spun alloy ribbons with a continuous length, a thickness of about 30 μm and a width of about 25 mm are successfully obtained. The microstructures of the as-spun alloy ribbons are characterized by XRD, SEM and TEM. The electrochemical hydrogen storage characteristics of the as-spun alloy ribbons were tested by an automatic galvanostatic system. The electrochemical impedance spectra (EIS) are plotted by an electrochemical workstation (PARSTAT 2273). The hydrogen diffusion coefficients in the alloys are calculated by virtue of potential-step method. The results show that no amorphous structure is detected in the as-spun Mn-free alloy, whereas the as-spun alloys containing Mn display a nanocrystalline and amorphous structure. The amorphization degree of the alloy increases with rising spinning rate, suggesting that the substitution of Mn for Ni facilitates the glass formation in the Mg 2Ni-type alloy. The substitution of Mn for Ni markedly improves the electrochemical hydrogen storage performances of the Mg 2Ni-type alloy, enhancing both the discharge capacity and the electrochemical cycle stability. Furthermore, the high rate dischargeability (HRD), electrochemical impedance spectrum and potential-step measurements all indicate that the electrochemical kinetics of the alloy electrodes first increases then decreases with increasing amount of Mn substitution.

Influence of rapid quenching on hydrogen storage characteristics of nanocrystalline Mg 2Ni-type alloys

Nanocrystalline Mg 2Ni-type alloys with nominal compositions of Mg 20Ni 10- x Cu x ( x = 0, 1, 2, 3, 4, mass fraction, %) were synthesized by rapid quenching technique. The microstructures of the as-cast and quenched alloys were characterized by XRD, SEM and HRTEM. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system. The hydriding and dehydriding kinetics of the alloys were measured using an automatically controlled Sieverts apparatus. The results show that all the as-quenched alloys hold the typical nanocrystalline structure and the rapid quenching does not change the major phase Mg 2Ni. The rapid quenching significantly improves the electrochemical hydrogen storage capacity of the alloys, whereas it slightly impairs the cycling stability of the alloys. Additionally, the hydrogen absorption and desorption capacities of the alloys significantly increase with rising quenching rate.

Enhanced electrochemical characteristics of as-spun nanocrystalline and amorphous Mg 2Ni-type alloy electrodes

The nanocrystalline and amorphous Mg 2Ni-type electrode alloys with nominal compositions of Mg 2Ni 1− x Mn x ( x = 0, 0.1, 0.2, 0.3, 0.4) are synthesized by melt-spinning technique. The spun alloy ribbons with a continuous length, a thickness of about 30 μm and a width of about 25 mm are obtained. The structures of the as-spun alloy ribbons are characterized by XRD, SEM and TEM. The electrochemical characteristics as well as the electrochemical impedance spectrums (EIS) of the as-spun alloy electrodes are measured. The hydrogen diffusion coefficients ( D) in the alloys were obtained by virtue of potential-step method. The results show that the as-spun ( x = 0) alloy holds a typical nanocrystalline structure, whereas the as-spun ( x = 0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni evidently intensifies the glass forming ability of the Mg 2Ni-type alloy. The substitution of Mn for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, involving the discharge capacity and the electrochemical cycle stability. Furthermore, the high rate discharge ability (HRD), the electrochemical impedance spectrum (EIS) and the potential-step measurements all indicate that the electrochemical kinetics of the alloy electrodes first increases then decreases with rising the amount of Mn substitution.