Electrochemical Hydrogen Storage Research Articles

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.

Development on the Preparation and Application of Onion-like Carbon

Due to unique structure, onion-like carbon has excellent physical and chemical properties that brodens the application in carbon and carbon-based composite materials. The classification and the structure of onion-like carbon were firstly introduced. Its advantages and disadvantages of traditional preparation methods, including arc discharge, plasma, electron-beam radiation, chemical vapor deposition, nanodiamond annealing in vacuum, thermolysis, were summarized. Then, some new synthetic methods developed in recent years were also presented. Subsequently, the application of onion-like carbon on anode materials of lithium ion secondary battery, counter electrode materials of dye-sensitized solar cell, electrodes materials of electrochemical hydrogen storage and super capacitor, friction and wear, and catalyst fields was summarized. Finally, deficiencies of preparation and application on onion-like carbon were pointed out and future research were put forward.

Synthesis of La2(Ni1-xCox)7 (x = 0.05, 0.1, 0.2) Hydrogen Storage Alloys by the Electro-Deoxidation Technique

La2(Ni1-xCox)7 (x = 0.05, 0.1, 0.2) alloys were synthesized directly from sintered mixture of La2O3 + NiO + CoO in the molten CaCl2 electrolyte by the electro-deoxidation method at 850°C and the electrochemical hydrogen storage characteristics of the synthesized alloys were observed. Sintering (at 1200°C for 3 h) converted the hygroscopic La2O3 (by the reaction with NiO) into the non-hygroscopic LaNiO3, La3Ni2O6.5 and La4Ni3O9 depending on the Co content of the oxide mixture. The X-ray diffraction peaks indicated that La2NiO4 was the main La-Ni-O phase formed as a result of partial reduction or dissociation reaction to initiate the LaNi5 phase formation. The target La2Ni7 phase formed much later than LaNi5 phase probably due to the sluggish reduction of LaOCl. It was observed that La2(Ni1-xCox)7 (x = 0.05, 0.1, 0.2) alloys had promising discharge capacities changed between 227 mA h g−1 (La2(Ni0.95Co0.05)7) and 332 mA h g−1 (La2(Ni0.8Co0.2)7) depending on the alloy Co content. This work clearly indicated that the electro-deoxidation was very effective method in the synthesis of the hydrogen storage materials.

Hydrogen storage performances of LaMg11Ni + x wt% Ni (x = 100, 200) alloys prepared by mechanical milling

In order to improve the hydrogen storage performances of Mg-based materials, LaMg11Ni alloy was prepared by vacuum induction melting. Then the nanocrystalline/amorphous LaMg11Ni+xwt% Ni (x=100, 200) hydrogen storage alloys were synthesized by ball milling technology. The structure characterizations of the alloys were carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical hydrogen storage characteristics were tested by using programmed control battery testing system. The electrochemical impedance spectra (EIS), potentiodynamic polarization curves and potential-step curves were also plotted by an electrochemical workstation (PARSTAT 2273). The results indicate that the as-milled alloys exhibit a nanocrystalline and amorphous structure, and the amorphization degree of the alloys visibly increases with extending milling time. Prolonging the milling duration markedly enhances the electrochemical discharge capacity and cyclic stability of the alloys. The electrochemical kinetics, including high rate discharge ability (HRD), charge transfer rate, limiting current density (IL), hydrogen diffusion coefficient (D), monotonously decrease with milling time prolonging.

Hydrogen storage kinetics of as-cast and spun (Mg24Ni10Cu2)100–x Nd x (x = 0–20) alloys

Abstract (Mg24Ni10Cu2)100–x Nd x (x = 0, 5, 10, 15, and 20) alloys with nanocrystalline and amorphous structures were prepared by melt-spinning. X-ray diffraction and high-resolution transmission electron microscopy 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. Melt spinning significantly improves the gaseous and electrochemical hydrogen storage kinetics of the alloys. Furthermore, melt spinning enhances the diffusion ability of hydrogen atoms in the alloy, but it impairs the charge-transfer reaction on the surface of the alloy electrode, which gives rise to the high-rate dischargeability of the alloy electrode, first mounting up and then going down with the increase in spinning rate.

Effects of substituting La with M (M=Sm, Nd, Pr) on electrochemical hydrogen storage characteristics of A2B7-type electrode alloys

The partial substitution of M (M=Sm, Nd, Pr) for La was performed in order to ameliorate the electrochemical hydrogen storage performance of RE–Mg–Ni-based A2B7-type electrode alloys. The La0.8–xMxMg0.2Ni3.35Al0.1Si0.05 (M=Sm, Nd, Pr; x=0–0.4) electrode alloys were fabricated by casting and annealing and their microstructures were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The major phases (La, Mg)2Ni7 with the hexagonal Ce2Ni7-type structure and LaNi5 with the hexagonal CaCu5-type structure make up the basic microstructure of the experimental alloys. The discharge capacities of the as-cast and annealed alloys all gain their maximum values with the M (M=Sm, Nd, Pr) content varying. The electrochemical cycle stability of the as-cast and annealed alloys clearly rises with the M (M=Sm, Nd, Pr) content growing. Furthermore, the electrochemical kinetics of the alloys, including the high rate discharge ability, charge transfer rate, limiting current density and hydrogen diffusion coefficient, all present a increase trend at first and then decrease with the rising of M (M=Sm, Nd, Pr) content.

Electrochemical hydrogen storage properties of TixV65−xNi35 (x=45, 55) alloys produced by rapid-quenching

Electrochemical discharge performances of TixV65−xNi35 (x=45, 55) alloy are measured by electrochemical measurements at galvanostatic conditions, and alloy ribbon is prepared by rapid-quenching under argon atmosphere. XRD analysis of TixV65−xNi35 (x=45) alloy shows that the Ti45V20Ni35 (x=45) is mostly the amorphous phase, V-based solid solution phase with BCC structure phase and a negligible amount of (Ni, V) phase. While x=55, namely the Ti55V10Ni35 alloy, mainly consists of the icosahedral quasicrystal (I-phase), face centered cubic (FCC) phase with Ti2Ni-type structure and V-based solid solution phase with BCC structure phase. In the electrochemical tests, the maximum discharge capacity of Ti45V20Ni35 is about 150.4mAh/g at a current density of 30mA/g. However, Ti55V10Ni35 alloy shows that the best discharge capacity is 221.8mAh/g under the same condition. In addition, it exhibits extraordinary cycling stability of 87.2% at 30 charge–discharge cycles. It can be found that the discharge capacity of the amorphous electrode is lower than those of the I-phase ones under the similar composition levels.

Effect of Ti/Cr content on the microstructures and hydrogen storage properties of Laves phase-related body-centered-cubic solid solution alloys

A series of BCC/C14 mixed phase alloys with the chemical composition of Ti13.6+xZr2.1V44Cr13.2−xMn6.9Fe2.7Co1.4Ni15.7Al0.3, x=0, 2, 4, 6, 8, 10, and 12, was fabricated, and their structural, gaseous phase and electrochemical hydrogen storage properties were studied. Raising the maximum pressure for measuring the gaseous hydrogen storage capacity allowed these alloys to reach full activation, and the maximum discharge capacities ranged from 375 to 463mAhg−1. As the Ti/Cr ratio in the alloy composition increased, the maximum gaseous hydrogen storage capacity improved due to the expansion in both BCC and C14 unit cells. However, reversibility decreased due to the higher stability of the hydride phase, as indicated by the lower equilibrium pressures measured for these alloys. As with most other metal hydride alloys, the electrochemical capacities measured at 50 and 4mAg−1 fell between the boundaries set by the maximum and reversible gaseous hydrogen storage capacities. The poorer high-rate dischargeability observed with higher Ti/Cr ratios was attributed to the lower surface exchange current (less catalytic). Two other negative impacts observed with higher Ti/Cr ratios in the alloy composition are poorer cycle stability and lower open-circuit voltage.

Effects of additive Pd on the structures and electrochemical hydrogen storage properties of Mg67Co33-based composites or alloys with BCC phase

Mg67Co33 and Mg67Co33–Pd composites/alloys prepared by ball milling for 120h possess nano-crystalline with body-centered cubic (BCC) structure, which was verified by high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) analyses. The introduced 5.0at.% Pd significantly lifts the initial discharge capacity from 10mAhg−1 of Mg67Co33 to maximum 530mAhg−1. Pd also drives the Mg67Co33–Pd composite forming a full BCC alloy during ball milling. The distribution of Pd gradually becomes homogeneous with the augmentation of the ball milling time according to the analyses by scanning electron microscopy-energy dispersive spectrometer (SEM-EDS). Exchange current density increased with the milling time and can be ascribed to the homogeneously dispersion of Pd over the surface. The introduced Pd also enhances the hydrogen diffusion coefficient of the Mg67Co33–Pd composites/alloys.

Hydrogen storage kinetics of nanocrystalline and amorphous Cu—Nd-added Mg2Ni-type alloys

The (Mg24Ni10Cu2)100—xNdx (x=0, 5, 10, 15, 20) alloys with nanocrystalline and amorphous structures were prepared by melt spinning technology. The structures of the as-cast and spun alloys were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The effects of Nd content and spinning rate on the structures and hydrogen storage kinetics of the alloys were investigated. The results show that the as-spun Nd-free alloy displays an entire nanocrystalline structure, whereas the as-spun Nd-added alloys hold nanocrystalline and amorphous structures, suggesting that the addition of Nd facilitates the glass forming of the alloys. Both the Nd-addition and the melt spinning significantly improve the gaseous and electrochemical hydrogen storage kinetics of the alloys. The addition of Nd and melt spinning enhance the diffusion ability of hydrogen atoms in the alloy, but both of them impair the charge-transfer reaction on the surface of the alloy electrode, which makes the high rate discharge ability (HRD) of the alloy electrode first mount up and then go down with the growing Nd content and spinning rate.

Preparation of ZrMn2 hydrogen storage alloy by electro-deoxidation in molten calcium chloride

ZrMn2 alloy was electro-synthesized directly from cathode pellets compacted with powdered mixture of MnO2 and ZrO2 in molten calcium chloride. Sintering temperature, cell voltage and electrolysis time were the dominant factors that affected the characteristics of the final product. The results confirmed the formation of pure ZrMn2 alloy through the electro-deoxidation of the mixed oxide pellets at 3.1 V for 12 h in 900 °C CaCl2 melt. The X-ray diffraction (XRD) and cyclic voltammetry analysis suggested that the electro-deoxidation proceeded from the reduction of manganese oxides to Mn, followed by ZrO2 or CaZrO3 reduction on the pre-formed Mn to ZrMn2 alloy. The cyclic voltammetry measurements using powder microelectrode showed that the prepared ZrMn2 alloy has a good electrochemical hydrogen storage property.

Crystallographic and Electrochemical Hydrogen Storage Performances of La0.75Ce0.25Ni3.80Mn0.90Cu0.30(Fe0.43B0.57)x (x = 00.20) Alloys

Crystallographic and Electrochemical Hydrogen Storage Performances of La0.75Ce0.25Ni3.80Mn0.90Cu0.30(Fe0.43B0.57)x (x = 00.20) Alloys

Synthesis of novel ZnV₂O₄ hierarchical nanospheres and their applications as electrochemical supercapacitor and hydrogen storage material.

Hierarchical nanostructures (Hs) have recently garnered enormous attention due to their remarkable performances in catalysis, electronic devices, energy storage and conversion. Considering the advantage of hierarchical nanostructures, we have formulated a facile and template free method to synthesize novel hierarchical nanospheres (NHNs) of ZnV2O4. Both zinc and vanadium are earth abundant, relatively economical and can offer several oxidation states, which can render a broad range of redox reactions favorable for electrochemical energy storage applications. Keeping these points in mind, we investigated for the first time the electrochemical supercapacitor performance of NHNs. The electrochemical measurements were performed in 2 M KOH solution. The measured specific capacitance of ZnV2O4 electrode is 360 F/g at 1 A/g with good stability and retention capacity of 89% after 1000 cycles. Moreover, the hydrogen storage properties of NHNs were measured at 473, 573, and 623 K with an absorption of 1.76, 2.03, and 2.49 wt %. respectively. These studies pave the way to consider ZnV2O4 as prospective material for energy storage applications.

Structure and electrochemical hydrogen storage properties of Ti2Ni alloy synthesized by ball milling

The structure and the electrochemical hydrogen storage properties of amorphous Ti2Ni alloy synthesized by ball milling and used as an anode in nickel–metal hydride batteries were studied. Nominal Ti2Ni was synthesized under argon atmosphere at room temperature using a planetary high-energy ball mill. The structural and morphological characterization of the amorphous Ti2Ni alloy is carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical characterization of the Ti2Ni electrodes is carried out by the galvanostatic charging and discharging, the constant potential discharge, the open circuit potential and the potentiodynamic polarization techniques.The Ti2Ni alloy activation requires only one cycle of charge and discharge, regardless of the temperature.The electrochemical discharge capacity of the Ti2Ni alloy, during the first eight cycles, and at a temperature of 30°C, remained practically unchanged and a good held cycling is observed. By increasing the temperature, the electrochemical discharge capacity loss after eight cycles undergoes an increase and it is more pronounced for the temperature 60°C.At 30°C, the anodic corrosion current density is 1mAcm−2 and then it undergoes a rapid drop, remaining substantially constant (0.06mAcm−2) in the range 40–60°C, before undergoing a slight increase to 70°C (0.3mAcm−2). This variation is in good agreement with the maximum electrochemical discharge capacity values found for the different temperatures.By increasing the temperature, the difference between the OCP curves corresponding to C/10 and C/30 regimes undergoes significant growth, reaching a maximum value (ΔEOCV=10.3mV) at 60°C before undergoing a decrease at 70°C.A good correlation is found between the evolutions of the corrosion current density with the maximum discharge capacity on one hand and on the other hand with the ΔEOCV, according to the temperature. The effect of temperature on the different electrochemical parameters (Icorr, Cmax, ΔEOCV) and the various correlations found between them allows us to optimize the performance of the battery and provide proper operation under the good experimental conditions.

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.

A nanostructured Ni/graphene hybrid for enhanced electrochemical hydrogen storage

To fabricate electrochemical hydrogen storage materials with delaminated structure, the graphene oxide (GO) in the ethylene glycol solution was reassembled in the presence of the precursor of Ni nanoparticles, and then, the reassembled hybrid was reduced under hydrogen atmosphere to obtain Ni/graphene hybrid. X-ray diffraction patterns and X-ray absorption spectscopic (XAS) analysis clearly show that Ni nanoparticles in Ni/graphene hybrid maintain its nanosized nature even after hybridization with graphene nanosheet (GNS). According to the TEM analysis, the Ni nanoparticles with an average size of 5.2nm are homogeneously distributed onto the GNS in such a way that the nanoporous structure with much amount of void spaces could be fabricated. The obtained Ni/GNS exhibits a hydrogen storage capacity of 160mAh/g, while the specific capacity of the graphene nanosheet was only 21mAh/g. A flexible delaminated structure of Ni/GNS nanocomposite could provide additional intercalation sites for accommodation of hydrogen, leading to the enhancement of hydrogen storage capacity.

The preparation of Co9S8 and CoS2 nanoparticles by a high energy ball-milling method and their electrochemical hydrogen storage properties

Two different Co–S compounds with enhanced hydrogen storage properties, Co9S8 and CoS2, were prepared by ball-milling mixtures of Co metal and S powder. X-ray diffractometry, scanning electron microscopy and transmission electron microscopy were used to show that specific molar ratios of Co:S and ball-milling speeds and times result in pure Co9S8 and CoS2, thus overcoming a long-standing inability to obtain pure Co–S compounds via ball-milling. A galvanostatic charge–discharge process and cyclic voltammetry measurements showed that the as-obtained Co9S8 and CoS2 nanoparticles have enhanced electrochemical hydrogen storage capacities of 1.79 and 1.57 wt% hydrogen, respectively, which are higher than those previously reported. In addition, based on the corresponding X-ray photoelectron spectroscopy and cyclic voltammetry measurements, a new electrochemical hydrogen storage mechanism for the two Co–S compounds was proposed and discussed.

Improved electrochemical hydrogen storage properties of Mg-Y thin films as a function of substrate temperature

Pd-capped Mg78Y22 thin films have been prepared by direct current magnetron co-sputtering system at different substrate temperatures and their electrochemical hydrogen storage properties have been investigated. It is found that rising substrate temperature to 60 °C can coarsen the surface of thin film, thus facilitating the diffusion of hydrogen atoms and then enhancing its discharge capacity to ~1725 mAh·g−1. Simultaneously, the cyclic stability is effectively improved due to the increased adhesion force between film and substrate as a function of temperature. In addition, the specimen exhibits a very long and flat discharge plateau at about −0.67 V, at which nearly 60% of capacity is maintained. The property is favorable for the application in metal hydride/nickel secondary batteries. The results indicate that rising optimal substrate temperature has a beneficial effect on the electrochemical hydrogen storage of Mg-Y thin films.

Effect of Ni, Fe and Fe-Ni alloy catalysts on the synthesis of metal contained carbon nano-onions and studies of their electrochemical hydrogen storage properties

Three types of carbon nano-onions (CNOs) including Ni@CNOs, Fe3C@CNOs and Fe0.64Ni0.36@CNOs nanoparticles have been synthesized by catalytic decomposition of methane at 850 °C using nickel, iron and iron-nickel alloy catalysts. Comparative and systematic studies have been carried out on the morphology, structural characteristics and graphitic crystallinity of these CNOs products. Furthermore, the electrochemical hydrogen storage properties of three types of CNOs have been investigated. Measurements show that the Ni@CNOs have the highest discharge capacity of 387.2 mAh/g, corresponding to a hydrogen storage of 1.42%. This comparison study shows the advantages of each catalyst in the growth of CNOs, enabling the controllable synthesis and tuning the properties of CNOs by mediating different metals and their alloy for using in the fuel cell system.

Influences of substituting Ni with M (M=Cu, Co, Mn) on gaseous and electrochemical hydrogen storage kinetics of Mg20Ni10 alloys

In this work, a comprehensive comparison regarding the impacts of M (M=Cu, Co, Mn) substitution for Ni on the structures and the hydrogen storage kinetics of the nanocrystalline and amorphous Mg20Ni10−xMx (M=Cu, Co, Mn; x=0–4) alloys prepared by melt spinning has been carried out. The analysis of XRD and TEM reveals that the as-spun (M=None, Cu) alloys display an entire nanocrystalline structure, whereas the as-spun (M=Co, Mn) alloys hold a mixed structure of nanocrystalline and amorphous structure when M content x=4, indicating that the substitution of M (M=Co, Mn) for Ni facilitates the glass formation in the Mg2Ni-type alloy. Besides, all the as-spun alloys have a major phase of Mg2Ni but M (M=Co, Mn) substitution brings on the formation of some secondary phases, MgCo2 and Mg phases for M=Co as well as MnNi and Mg phases for M=Mn. Based upon the measurements of the automatic Sieverts apparatus and the automatic galvanostatic system, the impacts engendered by M (M=Cu, Co, Mn) substitution on the gaseous and electrochemical hydrogen storage kinetics of the alloys appear to be evident. The gaseous hydriding kinetics of the alloys first rises and then declines with the growing of M (M=Cu, Co, Mn) content. Particularly, the M (M= Mn) substitution results in a sharp drop in the hydriding kinetics when x=4. The M (M=Cu, Co, Mn) substitution ameliorates the dehydriding kinetics dramatically in the order (M=Co)>(M=Mn)>(M=Cu). The electrochemical kinetics of the alloys visibly grows with M content rising for (M=Cu, Co), while it first increases and then declines for (M=Mn).