Electrochemical Hydrogen Storage Behaviors Research Articles

Preparation of Co/Ni nanoparticles doped g-C3N4 for improving the electrochemical hydrogen storage performance of Co0.9Cu0.1Si alloy

A facile liquid-phase reduction strategy was used to prepare cobalt and nickel nanoparticles doped graphitic carbon nitride (g-C3N4). Co0.9Cu0.1Si alloy was manufactured by mechanical alloying. Subsequently, a series of g-C3N4, Co-g-C3N4 and Ni-g-C3N4 modified Co0.9Cu0.1Si composites were fabricated via ball milling. The electrochemical hydrogen storage behaviors of metal doped g-C3N4/Co0.9Cu0.1Si composite electrodes were studied for the first time. Ultimately, Co0.9Cu0.1Si + Co-g-C3N4 and Co0.9Cu0.1Si + Ni-g-C3N4 revealed preferable discharge capacity of 575.8 mA h/g and 561.0 mA h/g than Co0.9Cu0.1Si + g-C3N4 and conventional Co0.9Cu0.1Si electrodes. The g-C3N4 offered more electrochemical active sites and beneficial interface for charge transfer. The metal particles within g-C3N4 further improved the electrocatalytic activity. The metal nanoparticles and g-C3N4 played synergistic effect in enhancing the hydrogen diffusion and electrochemical behavior of Co0.9Cu0.1Si alloy. Moreover, Co-g-C3N4 and Ni-g-C3N4 modified Co0.9Cu0.1Si also demonstrated better capacity retention, high-rate dischargeability (HRD) and kinetics properties. Accordingly, Co/Ni nanoparticles doped g-C3N4 can be considered as effective material for hydrogen storage alloy modification.

First-principles analysis of electrochemical hydrogen storage behavior for hydrogenated amorphous silicon thin film in high-capacity proton battery

Silicon material electrodes as proton carriers for high-capacity proton battery have only been proposed for such a short period of time that their physicochemical properties and electrochemical hydrogen storage behavior during charge and discharge processes remain nearly uncharted territory. Herein, the hydrogenated amorphous silicon (a-Si:H) thin film electrodes are prepared by radio frequency sputtering followed by ex-situ hydrogenation. The electrochemical properties of a-Si:H electrodes are tested experimentally, and the electrochemical hydrogen storage behaviors of a-Si:H electrodes are analyzed by first-principles calculations. The results show that the hydrogenation process significantly increases the electrochemical capacity of the electrodes and reduces the band gap of the electrode structure. The electrode exhibits weak conductivity during the initial charging, but the instability of the electrode electronic structure during the later charging results in a slight fluctuation of the electrochemical charging process. The a-Si:H electrode have better electrochemical hydrogen storage/release reversibility than non-hydrogenated electrodes, but this reversibility is weakened by oxygen atoms covered on the electrode surface. The electrochemical hydrogen storage process is easier to accomplish than the electrochemical desorption process of hydrogen evolution reaction for the a-Si:H electrodes. The a-Si:H thin film electrode is more stable on the Ni(111) substrate surface and the good conductivity of the electrode/substrate interface provides convenient conditions for the free transport of electrons in the electrochemical charge/discharge processes. We believe that these results perfectly explain the microscopic mechanisms responsible for the electrode reaction and electrochemical behavior of a-Si:H electrodes in this type of proton battery, and have a certain reference value in understanding the physicochemical properties and electrochemical hydrogen storage behavior of silicon material electrodes applied to other types of batteries during charge/discharge processes.

A new approach to synthesize ammonium uranate decorated reduced graphene oxide nanosheets and their performance in electrochemical hydrogen storage

In this research, the ternary solid phase of UO3·NH3H2O has been successfully synthesized via a simple and novel hydrothermal method under ammonia atmosphere, and identified as an ammonium uranate. Moreover, the decorated reduced graphene oxide network with ammonium uranate, UO3/rGO nanocomposite, was prepared and used to hydrogen sorption and storage. On the other word, for the first time, the electrochemical hydrogen storage behavior of the uranium compounds was evaluated by chronopotentiometry technique. Additionally, in order to further investigate the effect of ammonium uranate nanoparticles on the hydrogen storage property of UO3/rGO, two ratios of UO3:rGO in the as-made nanocomposites, 1:3 (UrGO3) and 1:10 (UrGO10), were studied. On this basis, the maximum discharge capacity was observed for the UrGO3 at 16,343 mAh/g after 20 cycles. The FE-SEM images indicated the UrGO3 nanosheets consist of the hierarchical plate-like pores, in a good agreement with BET analysis. According to the results, UO3 is introduced as a good candidate to improve the performance of electrochemical hydrogen storage on the graphene surface.

The study of electrochemical hydrogen storage behavior of the UiO-66 framework on the metal/reduced graphene oxide substrate

Feasible and safe storage of hydrogen as a clean and renewable energy carrier, is one of the main challenges to be tackled using highly efficient hydrogen storage materials. A new nanocomposite with a zirconium-based metal–organic framework is synthesized for the first time to improve the hydrogen storage capacity of the graphene oxide used to design graphene layers with metal. To this end, graphene oxide (GO) is combined with some metal ions (M), including Cu2+, Ni2+, Co2+and Ag+. The results of hydrogen storage capacity show that among different M/rGO, the introduction of Ag is the best choice. Eventually, the hydrogen storage capacity of 25 wt% Ag/rGO is 1600 mAhg−1, which has had an increase of more than 4 times as compared to the GO electrode. Besides, UiO-66/Ag/rGO nanocomposites are prepared at room temperature. The hydrogen storage capacity of UiO-66/Ag/rGO (MUiO-66/MAg/rGO = 5:1), reached from 250 mAhg−1 (0.94 wt%) to 6100 mAhg−1 (22.94 wt%) after 20 cycles, which was significantly enhanced; namely, about 3.8 times higher than Ag/rGO sample and approximately 2 times higher than UiO-66 sample. Furthermore, adding Ag/rGO to UiO-66 improved the porosity resulting in increasing the specific surface area of UiO-66/Ag/rGO (473 m2g−1) significantly, as compared to pure Ag/rGO (27.1 m2g−1).

Electrochemical hydrogen storage, mechanical and thermal behaviors of novel Mg-based alloy

In this study, Mg65Ni25Y5B5 metallic glass synthesized by using the melt-spinning technique was examined in terms of its electrochemical hydrogen-storage characteristics and mechanical and thermal behaviors. The X-ray diffraction and scanning electron microscopy results indicated that the alloy ribbon has a fully amorphous structure. The thermal behavior of the alloy ribbon was determined using flash differential scanning calorimetry (DSC). According to flash DSC results, the amorphous alloy ribbon exhibited a distinct glass transition temperature (T g) and a wide supercooled liquid region (ΔT x = T x − T g) before crystallization. Accordingly, T g and ΔT x are 195 and 63°C, respectively. The mechanical behavior of the magnesium (Mg)-based alloy at room temperature was determined by means of a Vickers microhardness (HV) tester. The microhardness value of the alloy ribbon was measured as 336.8 HV. The discharge capacity of the Mg65Ni25Y5B5 alloy reached 313 mAh/g. The cycle stability revealed that the alloy ribbon protected at least 76.7% of its initial discharge capacity at the 12th charge–discharge cycle.

Architecturally robust tubular nano-clay grafted Li0.9Ni0.5Co0.5O2-x/LiFeO2 nanocomposites: New implications for electrochemical hydrogen storage

To meet the demand for sustainable energy development, focusing on storage systems of clean energy like hydrogen is a priority. However, the utilization of new sorbent materials for an in-depth understanding of hydrogen storage mechanisms remains lacking. Herein, a novel composite electrode based on halloysite nanotube-Li0.9Ni0.5Co0.5O2-x/LiFeO2 (HNT-LNCO/LFO) nanostructures with superior electrochemical hydrogen storage behavior is developed via two-pot synthesis strategy, in which the HNT bridges with rich active sites serve as a natural clay support for LNCO/LFO electrocatalysts to equip improved hydrogen sorption kinetics through the spillover phenomena and redox coupling effect. Varied parameters, such as fuel types, the molar ratio of fuel to nitrates, the concentration of the LNCO/LFO (mg/ml), and solvent were optimized to prepare HNT-LNCO/LFO nanocomposites with desired purity, structure, and morphology. These physicochemical changes were realized by a combination of X-ray Powder Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), High Resolution Transmission Electron Microscopy (HR-TEM), and Brunauer-Emmett-Teller (BET) analyses. Furthermore, the electrochemical nature of the proposed nanocomposites were probed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronopotentiometry charge–discharge (CCD) process in KOH medium. The effect of conductive LNCO/LFO contents (3.0 %, 5.0 % and 7.0 %) on the HNT substrate was evaluated with the discharge efficiency and hydrogen spillover mechanism. As a consequence, the LNCO/LFO nanoparticles and pristine HNT structures exhibited the hydrogen storage capacities of 499.67 and 84.05 mAhg−1 after 15 cycles, respectively. However, the contribution of LNCO/LFO nanoparticles with weight percent of 3.0 %, 5.0 % and 7.0 % in tubular matrix can produce the discharge efficiencies of 309.33, 437.34 and 132.25 mAhg−1 in three electrode cells, respectively. This systematic work will result in alternative insights of the well-designed HNT-based nanocomposites for highly efficient energy storage applications.

Influence of structural and chemical environmental factors on electrochemical hydrogen storage in carbon materials

The influences of pore size, specific surface area, and surface chemistry of carbon material as well as the pH value of electrolyte solution on the electrochemical hydrogen storage performances are investigated. Three types of carbon materials carrying micro-, meso- and macro- pores, respectively, were either commercial available or synthesized through the hard template method. Their electrochemical hydrogen storage behaviors are studied in acidic, neutral, and alkaline solutions. The results indicate that microporous carbon with a high specific surface area has great advantages in hydrogen storage capacity, stability, and cycle performance. Moreover, nitrogen-doped porous carbon can not only improve hydrogen storage capacity but also both rate and hydrogen storage stability. The neutral electrolyte provides a larger voltage window while the alkaline media exhibits positive impacts on the hydrogen storage capacity. At the same time, regardless of the pH value of the electrolytes, the larger the specific surface area of the carbon material, the higher the hydrogen storage capacity.

Sol-gel synthesis of DyFeO3/CuO nanocomposite using Capsicum Annuum extract: Fabrication, structural analysis, and assessing the impacts of g-C3N4 on electrochemical hydrogen storage behavior

Nano-sized DyFeO3/CuO composites were fabricated via a green pechini sol-gel route using Capsicum annuum L. extract as a natural chelating agent. Capsicum annuum L. chelating agent contains a set of environmentally friendly biomolecules, which control the nucleus and the growth of formed crystals by creating a space barrier around the cations, and ultimately preventing the accumulation of nano-products. Changing of parameters in synthesis reaction consisting of chelating agents (natural and chemical) and calcination temperature, for its part, offer a righteous grip on the nano-composites dimension and morphology which pure DyFeO3/CuO nano-composites attained. The as-prepared DyFeO3/CuO nanostructures were investigated through Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET, vibrating sample magnetometer (VSM), and energy-dispersive X-ray (EDX) analysis in terms of structure, uniformity, porosity, shape, and size. The effect of adding CuO and graphite carbon nitride (g-C3N4) nanostructures was evaluated on discharge capacity and cyclic voltammetry methods. The attained DyFeO3/CuO/g-C3N4 nano-products could be utilized as a promising new nanocomposite for electrochemical hydrogen storage. It was found that DyFeO3/CuO/g-C3N4 nanocomposites have a special hydrogen storage accomplishment due to the synergistic effects of CuO and g-C3N4 components, which can increase the storage capability to 1600 mAhg−1 after 20 cycles by facilitating the hydrogen charge-discharge process.

Electrochemical hydrogen storage behavior of Ni-Ceria impregnated carbon micro-nanofibers

A hierarchical porous structured carbon micro-nanofiber containing the bimetallic configuration of the nickel (Ni) and ceria (CeO2) nanoparticles (NPs) was synthesized and tested for the electrochemical hydrogen (H2) storage capacity. The electrode exhibited a high H2 storage capacity of 498 mA h/g or 1.858% (w/w) at the charge-discharge current density of 500 mA/g. A mechanistic insight showcased the combined contributions of the high surface area containing activated carbon microfiber (ACF) substrate, the graphitic carbon nanofibers (CNFs), and the Ni and CeO2 NPs, towards the augmented electrochemical H2 storage capacity and cyclic stability of the fabricated Ni–CeO2–CNF/ACF electrode. Ni served as the catalyst for growing the CNFs via chemical vapor deposition as well as for storing H2 via spillover mechanism, while CeO2 created the charge carrier vacancies in the material. The measured cycle retention capacity of 99% and charge-discharge efficiency of 97.6% confirm the electrochemically stable characteristics of Ni–CeO2–CNF/ACF, and clearly indicate it to be an economically viable and efficient H2-storage material.

Electrochemical hydrogen storage behaviors of as-milled Mg–Ti–Ni–Co–Al-based alloys applied to Ni-MH battery

In the study, the hydrogen storing materials Mg–Ni-based Mg50-xTixNi45Al3Co2 (x = 0, 1, 2, 3, 4) + 50 wt% Ni (named Mg50-xTixNi45Al3Co2 (x = 0–4) + 50Ni) with nanocrystalline and amorphous structures were fabricated by the method of mechanical milling and designed for the negative electrode of Ni–MH batteries. The investigation aims at researching the function of Ti dosage on the electrochemical hydrogen storing characteristics and microstructure of the experimental specimens. The analysis of X-ray diffraction profiles and Scanning Electron Microscope images determines that the experiment specimens contain the major phase Mg2Ni and the minor phase MgNi2. The observation of TEM images reveals a fact that the specimens after ball-milling treatment consist of the nanocrystal and amorphism structures. The electrochemical tests show that as for the samples after ball-milling treatment, the discharge capacities of them gain the utmost value at the first circulate without activation treatment, and the increase of Ti dosage brings on an evident rise in the specimens’ discharge capacity and cycle stability. Concretely, as the Ti content alters from 0 to 4, the discharge capacities of the as-milled (20 h) sample increase from 405.0 to 519.4 mAh/g and capacity retention rate of 100th circulate (S100 = C100/Cmax) augments from 45% to 72%. What’s more, a series of measurements, such as the high rate discharge ability (HRD), the electrochemical impedance spectrum (EIS) as well as Tafel polarization curves etc. show that the electrochemical kinetics performances of as-milled specimens in this experiment have a trend of increasing first and then decreasing with the addition of Ti element.

Structure and electrochemical hydrogen storage behaviors of Mg–Ce–Ni–Al-based alloys prepared by mechanical milling

The influences of milling time and Ce content on the electrochemical property and microstructure of as-milled Mg1−xCexNi0.9Al0.1 (x = 0, 0.02, 0.04, 0.06, 0.08) + 50 wt%Ni alloys were investigated systematically. The as-milled alloys have an outstanding activation property. The cycle stability conspicuously grows up with milling time and Ce proportion increasing. The capacity retention rate at 100th cycle of x = 0.02 alloy augments from 47% to 63% when prolonging milling time from 5 to 30 h and it grows from 55% to 82% for the 30 h milled alloy with Ce content growing from 0 to 0.08. The discharge capacity of x = 0.02 alloy grows up invariably with milling time prolonging, while that of the 30 h milled alloys has the maximal value of 578.4 mAh/g with Ce content increasing. Moreover, the electrochemical kinetic properties of alloys significantly improve with milling duration extending, while they have the maximal values with Ce proportion varying.

Electrochemical hydrogen storage behaviors of as-milled Mg-Ce-Ni-Al-based alloys applied to Ni-MH battery

For improving electrochemical performances of Mg-Ni-based alloys at ambient temperature, a portion of Mg was succeeded by Ce and the surface modification treatment was conducted by mechanical coating Ni. The nanocrystalline and amorphous Mg1-xCexNi0.9Al0.1 (x = 0, 0.02, 0.04, 0.06, 0.08) + 50 wt%Ni metals were prepared. Impacts of Ce content and milling duration on the structure and electrochemical hydrogen storage properties have been researched. The results exposed that, the as-milled alloys can absorbing/desorbing hydrogen electrochemically very well at ambient temperature. Activation is not necessary as the first cycle can reach the maximal discharge capacity. Through 5 and 20 h milling, the maximum discharge capacities of alloys are 378.8 and 545.3 mAh/g, respectively. Cycling stability improves with Ce content and milling time growing. Specifically speaking, the retention rate of capacity at 100th cycle (S100 = C100/Cmax) ascends from 36% to 66% for 5 h milled alloy and from 48% to 76% for 20 h milled alloy with Ce content growing from 0 to 0.08. Furthermore, many indexes such as electrochemical impedance spectrum, potentiodynamic polarization curves, high rate discharge ability, potential-step measurements, etc. proved that varying Ce content makes the alloys get their best electrochemical kinetic property.

Effects of milling duration on electrochemical hydrogen storage behavior of as-milled Mg–Ce–Ni–Al-based alloys for use in Ni-metal hydride batteries

Mg-based hydrogen storage alloys are regarded as ideal materials for use as the negative electrode in nickel-metal hydride batteries. However, their poor electrochemical de-/hydriding performance at room temperature is a problem. Methods comprising the partial substitution with Ce for Mg and surface modification by mechanical coating with Ni have been applied to address the problem. In this study, nanocrystalline and amorphous Mg1-xCexNi0.9Al0.1 (x = 0, 0.02, 0.04, 0.06, 0.08) + 50 wt%Ni (named Mg1-xCexNi0.9Al0.1 (x = 0, 0.02, 0.04, 0.06, 0.08) + 50Ni) alloys were synthesized by mechanical milling. Electrochemical testing showed that the samples exhibited outstanding electrochemical de-/hydriding performance at room temperature. The maximum discharge capacities were obtained after only one de-/hydriding cycle and without any need for activation. The discharge capacity and cycle stability increased with the milling duration. In particular, for the alloy where x = 0.04, the discharge capacity increased from 378.8 to 578.4 mAh/g, and the capacity retention rate after the 100th cycle increased from 51% to 69% as the milling duration increased from 5 to 30 h. Furthermore, measurements based on the high rate discharge ability, electrochemical impedance spectra, potentiodynamic polarization curves, and potential-step measurements demonstrated that the electrochemical kinetic properties of the alloys could be improved by extending the duration of milling.

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

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

Characterization of hydrogen storage behavior of the as-synthesized p-type NiO/n-type CeO2 nanocomposites by carbohydrates as a capping agent: The influence of morphology

This study proposes a p-type/n-type heterojunction system for electrochemically hydrogen storage. The electrochemical investigation was done as a simple method to evaluate storage capacity. The p-type NiO/n-type CeO2 mesoporous nanocomposites were prepared via a facile thermal decomposition way that is better than the carbohydrates as a green capping agent. For the first time, the electrochemical hydrogen storage behavior of this nanocomposite was evaluated by chronopotentiometry technique in a potassium hydroxide aqueous solution (6 M KOH) under 1 mA current. The electrochemical measurements display that the hydrogen storage capacity is largely dependent on the design of the nanostructures. Sample No. 2 with the plate-like architecture has higher hydrogen storage capacity than sample No. 1 having particle architecture. The plate-like architecture increases the storage capacity by reducing the diffusion pathway, increasing the surface area, and buffering the volume change during cycling. The hydrogen storage capacity for sample No. 1 and 2 was obtained ≈5500 and 6850 mAh/g, respectively.

Structure and electrochemical hydrogen storage behaviors of RE-Mg-Ni-Co-Al-based AB2-type alloys prepared by melt spinning

The AB2-type La0.8-xCe0.2YxMgNi3.4Co0.4Al0.1 (x = 0–0.2) alloys were successfully fabricated by melt spinning. The changes of the thickness, the structure and electrochemical hydrogen storage behaviors caused by different spinning rate were investigated. The alloys have a base phase LaMgNi4 phase and an impurity phase LaNi5 phase. Melt spinning has impacts both on the macro characteristics and microstructures. The results show that increasing spinning rate results in a reduction of the average thickness of the ribbons, an increase of lattice constants and a decrease of the grains size. Moreover, it incurs the content of the LaMgNi4 phase increase and that of the LaNi5 phase decrease. The alloys achieve to the highest discharge capacities at the initial electrochemical cycle. The discharge capacity visibly declines, whereas the life-span considerably grows with increasing spinning rate. Furthermore, the electrochemical kinetics increase to a maximum value and decrease again with spinning rate growing.

Electrochemical hydrogen storage behaviors of the nanocrystalline and amorphous Nd-Cu-added Mg2Ni-type alloy electrodes applied to Ni-MH battery

In order to ameliorate the electrochemical characteristics of Mg2Ni-type alloy, the elements Cu and Nd are added in the alloy. The nanocrystalline and amorphous Mg2Ni-type alloys with the composition of (Mg24Ni10Cu2)100–xNdx (x = 0, 5, 10, 15, 20) are prepared by melt spinning technology. The effects of Nd content and spinning rate on structures and electrochemical performances of the alloys are investigated. X-ray diffraction (XRD) and transmission electron microscopy (TEM) reveal that the as-spun Nd-free alloy displays an entirely nanocrystalline structure, whereas the as-spun Nd15 alloy, differing from Nd0 alloy, exhibits nanocrystals embedded in an amorphous matrix. This suggests that the addition of Nd facilitates the amorphous formation ability of the alloys. The electrochemical measurement indicates that both adding Nd and melt spinning significantly improve the electrochemical performances of the alloys, involving the discharge potential characteristics, discharge capacity, cycle stability, and the high rate dischargeability (HRD). The Nd addition and melt spinning enhance the diffusion ability of hydrogen atoms in the alloy, but both of them impair the charge-transfer ability on the surface of the alloy electrode, which gives rise to the HRD values first mounting up and then going down with the growing of the Nd content and the spinning rate.

Promising gaseous and electrochemical hydrogen storage properties of porous Mg-Pd films under mild conditions.

In this paper, the gaseous and electrochemical hydrogen storage properties of 200 nm Mg-Pd thin films with different morphologies have been investigated. The results show that Mg-Pd films become porous with the increase of substrate temperature. Porous Mg-Pd films exhibit superior gaseous and electrochemical hydrogen storage behaviors under mild conditions, including rapid hydrogen sorption kinetics, a large hydrogen storage amount, high electrochemical discharge capacity, and a fast hydrogen diffusion rate. The excellent behaviors of porous Mg-Pd films might be ascribed to the significantly shortened hydrogen diffusion paths and the large contact areas between the hydrogen gas and the solid Mg phases, which are elucidative for the development and applications of thick Mg-Pd films.

Gaseous and electrochemical hydrogen storage behaviors of nanocrystalline and amorphous Nd-added Mg2Ni-type alloys

Melt spinning technology was used to prepare the Mg2Ni-type (Mg24Ni10Cu2)100−x Nd x (x = 0, 5, 10, 15, 20) alloys in order to obtain a nanocrystalline and amorphous structure. The effects of the spinning rate on the structures and gaseous and electrochemical hydrogen storage behaviors of the alloys were investigated. The analysis of X-ray diffraction (XRD), transmission electron microscope (TEM), and scanning electron microscope (SEM) linked with energy-dispersive spectroscopy (EDS) reveals that all the as-cast alloys hold a multiphase structure, involving the main phase Mg2Ni and some secondary phases such as Mg6Ni, Nd5Mg41, and NdNi. The as-spun Nd-free alloy displays an entire nanocrystalline structure, whereas the as-spun Nd-added alloys hold a nanocrystalline and amorphous structure, and the amorphization degree visibly increases with the spinning rate increasing. The melt spinning ameliorates the hydrogen storage performances of the alloys dramatically. When the spinning rate rises from 0 (the as-cast was defined as the spinning rate of 0 m·s−1) to 40 m·s−1, the discharge capacity increases from 86.4 to 452.8 mAh·g−1, the S 20 (the capacity maintain rate at 20th cycle) value increases from 53.2 % to 89.7 %, the hydrogen absorption saturation ratio (R 5 a , a ratio of the hydrogen absorption quantity in 5 min to the saturated hydrogen absorption capacity) increases from 36.9 % to 91.5 %, and the hydrogen desorption ratio (\(R_{ 1 0}^{d}\), a ratio of the hydrogen desorption quantity in 10 min to the saturated hydrogen absorption capacity) increases from 16.4 % to 47.7 % for the (x = 10) alloy, respectively.

Well‐defined Sb2S3 nanostructures: citric acid‐assisted synthesis, electrochemical hydrogen storage properties

Well‐defined (three‐dimensional) 3‐D dandelion‐like Sb2S3 nanostructures consisted of numerous nanorods have been achieved via a facile citric acid‐assisted solvothermal process. The as‐prepared products were characterized by X‐ray diffraction (XRD), field‐emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high‐resolution TEM (HRTEM), respectively. The influence factors of the formation of the hierarchical Sb2S3 nanostructures are discussed in details based on FESEM characterizations. By simply controlling the quantity of citric acid, the nucleation and growth process can be readily tuned, which brings the different morphologies and nanostructures of the final products. On the basis of a series of contrastive experiments, the aggregation‐based process and anisotropic growth mechanism are reasonably proposed to understand the formation mechanism of Sb2S3 hierarchical architectures with distinctive morphologies including nanorods, and dandelion‐like nanostructures. Charge‐discharge curves of the obtained Sb2S3 nanostructures were measured to investigate their electrochemical hydrogen storage behaviors. It revealed that the morphology played a key role on the hydrogen storage capacity of Sb2S3 nanostructure. The dandelion‐like Sb2S3 nanostructures exhibited higher hydrogen storage capacity (108 mAh g−1) than that of Sb2S3 nanorods (95 mAh g−1) at room temperature.