Performance Of Hydrogen Storage Alloys Research Articles

Optimization of LaNi5 hydrogen storage properties by the combination of mechanical alloying and element substitution

LaNi5 is a commercial hydrogen storage alloy with great potential. But its performance still needs to be optimized to meet the standard proposed by the US Department of Energy. Element substitution is a very important method to optimize the performance of hydrogen storage alloys, especially suitable for AB5 alloys. As a novel method to produce nanocrystalline hydrogen storage alloys, mechanical alloying is also often applied to optimize the properties of hydrogen storage alloys.In this work, first of all, the simulation method based on first principles is applied to predict the performance of 8 elements substituting Ni respectively, and select the most suitable element to substitute Ni. Then the phase composition characterization, hydrogen storage performance tests and electrochemical performance tests were carried out. It was found that mechanical alloying can greatly improve the hydrogen storage performance of LaNi5, and different ball milling times can bring about different performance changes. After adding Cr to the ball-milled LaNi5, the properties of the formed LaNi4Cr were further improved.

Preparation of CO2‐activated Porous Graphene for Enhancing the Electrochemical Hydrogen Storage Properties of Co9S8 Material

AbstractIn this work, Co9S8 hydrogen storage material was synthesized by mechanical alloying. To improve the electrocatalytic activity and conductivity of Co9S8, a series of porous reduced graphene oxide (PRGO) materials were fabricated via a facile CO2 activation treatment of RGO at different processing times. The composites of Co9S8 doping with different amount of PRGO were manufactured through ball milling. During the electrochemical hydrogen storage test, the porous Co9S8+PRGO exhibited higher discharge capacity than Co9S8+NRGO and conventional Co9S8. Moreover, the CO2 activation time and additive amount of PRGO had significant impact on the electrochemical properties of Co9S8. Ultimately, the electrode of 6 wt.% PRGO‐2 modified Co9S8 attained the optimum discharge capacity of 653 mAh/g. The special porous structure and high specific surface area of porous graphene could provide more electrochemical active sites and facilitate the hydrogen diffusion. After PRGO modification, the cycling stability, high‐rate dischargeability (HRD) and kinetic properties of Co9S8 were also enhanced. It can be concluded that porous graphene possesses better effect than conventional graphene in improving the performance of hydrogen storage alloy.

Compositionally complex doping for low-V Ti-Cr-V hydrogen storage alloys

Ti-V-based BCC solid solution alloys, represented by Ti-Cr-V alloys, are considered as promising hydrogen storage materials due to their high hydrogen storage capacity (over 4 wt%) at room temperature. However, the difficult activation, low effective hydrogen desorption capacities, poor P-C-T plateau characteristics, and high cost remain significant problems for their practical applications. Herein, we present a new compositionally complex (high-entropy) doping strategy which was used to successfully fabricate a low-cost “Laves phase related BCC solid solution”, TiCrV0.7(Nb0.2Fe0.2Co0.2Ni0.2Mn0.2)0.2, that exhibits excellent activation performance and high effective hydrogen desorption capacity (Ce1atm: 2.21 wt%). The main BCC phase ensures high hydrogen storage capacity, while the minor secondary C14 phase plays a catalytic role and thus improves the hydrogen absorption kinetics. Furthermore, we confirmed that there is a synergistic effect of Nb, Fe, Co, Ni, and Mn elements in improving hydrogen storage performance. The dehydrogenation enthalpy ΔH of the heat-treated TiCrV0.7(Nb0.2Fe0.2Co0.2Ni0.2Mn0.2)0.2 is 37.5 kJ mol−1, which is significantly lower than previously reported Ti-Cr-V based systems, revealing a significant tendency towards easier dehydrogenation with high-entropy doping. This work offers a new alloying method for improving the hydrogen storage performance of hydrogen storage alloys.

Influence of heat exchanger structure on hydrogen absorption-desorption performance of hydrogen storage vessel

The influence of heat exchanger structure on hydrogen absorption-desorption performance of hydrogen storage vessel was studied, in which the AB5 (La0.25Ce0.75Ni4.4Al0.1Mn0.1Co0.4) hydrogen storage alloy was used as a typical representative. In order to obtain the data on reaction enthalpy, the PCT curve of the alloy was measured with three different temperatures, and the linear fitting was carried out according to the Van't Hoff relation curve. The SMCR (Spiral-mini-channel Reactor) reactor structure was adopted. The heat transfer method and its simplified model were studied by finite element method to explore the effect of size of heat transfer structure, particularly for heat pipe diameter, on the hydrogen absorption-desorption performance of hydrogen storage alloy in the vessel.

Significantly decreased stability of MgH2 in the Mg-In-C alloy system: Long-period-stacking-ordering as a new way how to improve performance of hydrogen storage alloys?

Hydrogen storage (HS) performance of Mg-In-CB alloys (CB – amorphous carbon) is studied. Indium concentration covers primary solid solution (Mg), two phase area (Mg) + β1 and also alloys containing ordered β structures. Seven Mg-In-CB alloys are prepared by ball-milling in hydrogen atmosphere. Kinetic curves and PCT isotherms are measured in the temperature interval from 200 °C to 375 °C. Hydrogen sorption experiments are done by the Sieverts method under the hydrogen gas pressure ranging from 0.1 MPa to 2.5 MPa. X-ray diffraction spectroscopy is used for structure investigation. Alloy with β’’ structure shows reversible amorphization during temperature cycling between about 100 °C and 350 °C. It is found that hydrogen sorption capacity varies between about 6 wt % H2 for (Mg) and 0.6 wt % H2 for β’’ structure. Hydride decomposition enthalpy calculated from desorption PCT experiments decreases to 54 ± 3 kJ × (mol H2)−1 and 57 ± 3 kJ × (mol H2)−1 for ordered alloys in the interval from 69 to 71 wt % In, and even down to 51.5 kJ × (mol H2)−1 for amorphous β’’ structure. Activation energy of desorption kinetics is also lowered in the ordered structure.

A layered porous Ni structure contributes to superior low-temperature performance of hydrogen storage alloys

The poor low-temperature performance of negative electrode materials— hydrogen storage alloys (HSAs) has impeded applications of nickel metal hydride batteries in new energy vehicles. Here, we propose a simple and effective strategy to improve low-temperature properties of the commercial HSA with HCl etching and heat treatment. The layered porous Ni surface structure formed during this process improves the electrochemical reaction kinetics, and thus results in a larger discharge capacity of 102.63 mAh g−1 at 233 K compared with those of bare (11.52 mAh g−1) and acid-corroded (43.00 mAh g−1) alloys. This method could be extended to enhance the low-temperature performance of other HSA systems.

A new strategy to improve the high-rate performance of hydrogen storage alloys with MoS2 nanosheets

Abstract The poor high-rate dischargeability of negative electrode materials (hydrogen storage alloys) has hindered applications of nickel metal hydride batteries in high-power fields, new-energy vehicles, power tools, military devices, etc. In this work, a new strategy is developed to improve the high-rate performance of hydrogen storage alloys by coating MoS 2 nanosheets on alloy surfaces. The capacity retention rate of the composite electrode reaches 50.5% at a discharge current density of 3000 mA g −1 , which is 2.7 times that of bare alloy (18.4%). The density functional theory simulations indicate that such an outstanding performance is derived from adjustments of ion concentrations at the electrode/electrolyte interface by MoS 2 nanosheets: (1) the higher OH − concentration facilitates the electrochemical reaction of MH ads + OH − − e − → M + H 2 O; and (2) the lower H + concentration leads to a large gradient between the electrode/electrolyte interface and interior of alloys, which is beneficial for the diffusion of atomic hydrogen during the discharging process.

In situ grown Co3O4 on hydrogen storage alloys for enhanced electrochemical performance

Co3O4 is an effective additive to enhance the electrochemical performance of hydrogen storage alloys. However, the low utilization efficiency has become a big challenge for direct adding Co3O4 powders into the alloys with mechanical mixing. Here, we report the in situ growth of Co3O4 on the alloy surface by using a facile and effective hydrothermal method. Compared with bare hydrogen storage alloys, the fabricated composite shows larger maximum discharge capacity, 326.37 vs. 302.62 mAh g−1, and enhanced high rate dischargeability with larger discharge capacity at a current density of 3000 mA g−1, 59.01 vs. 40.88 mAh g−1. These are contributed by the unique hybrid architecture of the composite: (1) the in situ grown Co3O4 nanosheets improve the catalytic activity and utilization efficiency of Co3O4 on the electrochemical reaction kinetics; and (2) the low-dimensional Co3O4 coatings seamlessly integrated with hydrogen storage alloys decrease the internal resistance and polarization of the hybrid electrode. Such a simple and novel method can also be extended to other energy storage devices.

Improvement of the rate performance of hydrogen storage alloys by heat treatments in Ar and H2/Ar atmosphere for high-power nickel–metal hydride batteries

The high-rate charge/discharge performance of L3DC alloy is improved by heat treatment in pure Ar or 10% H2/Ar atmosphere at 300°C and 400°C. L3DC, a commercially available LaNi5-type alloy, is used as the negative electrode for high-power nickel–metal hydride batteries. The structural modification, morphology, and surface composition of the heat-treated alloys are examined through X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray energy dispersive spectrometry (EDS). Electrochemical performance of the alloy is also tested with an electrochemical workstation and a charge/discharge tester. Results show that the low- and room-temperature rate discharge performance and high-temperature rate charge performance of the alloy can be improved by heat treatment in 10% H2/Ar atmosphere. Moreover, the low- and room-temperature rate charge performance and high-temperature rate discharge performance can only be enhanced by heat treatment in pure Ar atmosphere. Heat treatment can affect not only the speed of proton transport in the solid phase, but also the hydrogen reaction on the alloy surface.

Enhancement of electrocatalytic performance of hydrogen storage alloys by multi-walled carbon nanotubes for sodium borohydride oxidation

Catalytic electrodes consisting of MmNi0.58Co0.07Mn0.04Al0.02 (AB5-type alloy) and multi-walled carbon nanotubes (MWNTs) are studied for NaBH4 electrooxidation and are characterized by scanning electron microscope and X-ray diffractometer. The NaBH4 electrooxidation performance on the AB5/MWNTs electrode is tested by cyclic voltammetry and chronoamperometry methods. The electrode performance is significantly affected by the content of MWNTs and the optimized content of MWNTs is found to be 2 wt.%. The steady state current density for NaBH4 electrooxidation at the AB5/MWNTs (2 wt.%) electrode is about twice of that at the AB5 electrode without MWNTs. The utilization efficiency of NaBH4 at the AB5/MWNTs electrode is 61.5% higher than that at the pristine AB5 electrode. The enhanced electrocatalytic activity and NaBH4 utilization at the AB5/MWNTs (2 wt.%) electrode can be attributed to MWNTs, which acts as a hydrogen adsorbent to diminish hydrogen release.

Electrochemical performances of AB 5-type hydrogen storage alloy modified with Co 3O 4

Anodic electrodes with the mixture of hydrogen storage alloys and different contents of Co 3O 4 (2%, 4%, 6% and 8%, mass fraction) powders were made. The effects of Co 3O 4 on the electrochemical performance of the alloy electrodes were studied. The constant charge-discharge tests show that the discharge capacity of alloy electrodes with Co 3O 4 significantly increases, and the maximum discharge capacities of electrodes with 2%, 4%, 6% and 8% Co 3O 4 are higher than the electrode with no Co 3O 4 by 0.83%, 4.86%, 7.18% and 9.21%, accordingly. Linear polarization (LP) and electrochemical impedance spectroscopy (EIS) tests suggest that charge-transfer resistance decreases by the addition of Co 3O 4. Cyclic voltammogram (CV), scanning electron microscopy (SEM) and energy dispersive spectrum (EDS) tests indicate that Co 3O 4 can partly dissolve and experience a reversible oxidation-reduction process of Co to Co (OH) 2, leading to the improvement in the electrochemical performance of hydrogen storage alloy.