Hydrogen Absorption Rate Research Articles

Hydrogen Absorption Performance and O2 Poisoning Resistance of Pd/ZrCo Composite Film.

In order to enhance the hydrogen absorption performance and poisoning resistance of ZrCo to O2, Pd/ZrCo composite films were prepared by direct current magnetron sputtering. The results show that the initial hydrogen absorption rate of the Pd/ZrCo composite film increased significantly due to the catalytic effect of Pd compared with the ZrCo film. In addition, the hydrogen absorption properties of Pd/ZrCo and ZrCo were tested in poisoned hydrogen mixed with 1000 ppm O2 at 10-300 °C, where the Pd/ZrCo films maintained a better resistance to O2 poisoning below 100 °C. The mechanism of poisoning was investigated jointly by first-principles calculation combined with SEM-EDS elemental mapping tests. It is shown that the poisoned Pd layer maintained the ability to promote the decomposition of H2 into hydrogen atoms and their rapid transfer to ZrCo.

Hydrogen absorption-desorption properties and hydrolysis performance of MgH2-Zr3V3O0.6Hx and MgH2-Zr3V3O0.6Hx-C composites

In this work, the catalytic effect of additions of η-Zr3V3O0.6 mixed suboxide and the title intermetallic composite with graphite on the properties of MgH2 in the processes of hydrogen storage and hydrogen generation has been studied. The hydride composites were obtained by high-energy reactive ball milling (RBM). The samples were characterized by X-ray diffraction and scanning electron microscopy. The cycling performance of hydrogen desorption and absorption as well as hydrogen generation in the hydrolysis reaction were studied. We found that during the reactive ball milling the studied composites are able in a few minutes to absorb ∼6.5 wt% of hydrogen. The addition of Zr3V3O0.6 and Zr3V3O0.6 + С catalysts not only increases the rates of hydrogen absorption and release, but also lowers the activation energy and the temperature of hydrogen desorption. For a composite containing 10 wt% of suboxide and 3 wt% of graphite, the activation energy of hydrogen desorption determined by the Kissinger method was very low, just 58 kJ/mol, and this value is among the lowest described in the reference publications. We also show that the intermetallic additive forms the Zr3V3O0.6H∼10 hydride, which results in a higher gravimetric capacity of the composite as H storage material. The improved kinetics of hydrogen exchange and increased hydrogenation capacity at modest operating temperatures of 150–200 °C appear to be characteristic for the composites containing suboxide and graphite additions. The reason for the advanced performance is in the different the morphology of the synthesized samples, particularly the graphite-containing composites showing a more developed dispergation of the material (the fraction with a particle size of 1–3 μm is >80 wt%). We furthermore show that the synthesized materials can be used in the hydrolysis process resulting in hydrogen generation. The amount of hydrogen released from the hydride Mg-Zr3V3O0.6-C composite in the hydrolysis reaction reaches 1364 ml/g (the conversion degree is ∼85 % for the process duration of 120 min) when using 0.04 M MgCl2 solutions.

Numerical study on hydrogen and thermal storage performance of a sandwich reaction bed filled with metal hydride and thermochemical material

Hydrogen storage and release process of metal hydride (MH) accompany with large amount of reaction heat. The thermal management is very important to improve the comprehensive performance of hydrogen storage unit. In present paper, thermochemical material (TCM) is used to storage and release the reaction heat, and a new sandwich configuration reaction bed of MH-TCM system was proposed and its superior hydrogen and thermal storage performance were numerically validated. Firstly, the optimum TCM distribution with a volume ratio (TCM in inner layer to total) of 0.4 was derived for the sandwich bed. Then, comparisons between the sandwich reaction bed and the traditional reaction bed were performed. The results show that the sandwich MH-TCM system has faster heat transfer and reaction rate due to its larger heat transfer area and smaller thermal resistance, which results in the hydrogen storage time is shortened by 61.1%. The heat transfer in the reaction beds have significant effects on performance of MH-TCM systems. Increasing the thermal conductivity of the reaction beds can further reduce the hydrogen storage time. Moreover, improving the hydrogen inflation pressure can result in higher equilibrium temperature, which is beneficial for the enhancing heat transfer and hydrogen absorption rates.

Hydrogen storage property improvement of La–Y–Mg–Ni alloy by ball milling with TiF3

Ball milling the powders of Mg-based alloys with transition metal compounds is effective for improving their hydrogen storage performances. In this experiment, the alloys of La1.7Y0.3Mg16Ni + x wt.% TiF3 (x = 0–10) were prepared through mechanical milling technology. XRD, SEM, HRTEM and granulometry were used to measure the composition and microstructure of alloys. The isothermal hydrogen storage property was measured by a Sievert apparatus. The results reveal that the TiF3 additive in ball-milled samples transforms into MgF2 and TiH2 after the first hydrogen absorption. Adding TiF3 enhances the crystallinity and reduces the average particle and crystallite sizes of alloys, which is beneficial to accelerating hydriding and dehydriding kinetics. Adding 7 wt% TiF3 into alloy decreases the dehydrogenation activation energy from 72.2 to 64.0 kJ/mol and improves the hydrogen absorption rate at low temperatures, absorbing 3.50 wt% H in 0.5 min at 323 K.

Hydrogenation Behavior of Cr-Coated Resistance Upset Welds of E110 Zirconium Alloy

The hydrogenation behavior of Cr-coated resistance upset welds (RUW) of E110 zirconium alloy was investigated at 360, 450 and 900 °C and a hydrogen pressure of 2 bar. The deposition of Cr coating, via magnetron sputtering, can decrease the hydrogen absorption rate of an RUW Zr alloy. The activation energy for the hydrogen absorption of Cr-coated specimens (84 kJ/mol) is higher in comparison with uncoated ones (71 kJ/mol), which indicates the deceleration of the hydriding of welded Zr alloys in the case of Cr coating deposition. A Cr coating can limit the formation of radially oriented hydrides and the hardening of RUW specimens at 360 and 450 °C. No significant difference in the hydrogen absorption rate was found at 900 °C. The application of Cr coating deposition to protect resistance-upset-welded Zr alloys in a hydrogen atmosphere is discussed.

Characterizing hydrogen storage behavior of Mg-based materials catalyzed by S2− and O2− ions

Composites of Mg90Ce5Y5 + 5.0 wt % MoS2/MoO2 were produced by vacuum refining technology. The phase-composition and microstructure of the specimens were analyzed using X-ray diffraction, transmission electron microscopy, electron diffraction, and inductively coupled plasma optical emission spectrometry. The performance of hydrogen storage was analyzed using thermogravimetric and differential thermal analysis curves and a semi-automatic Sievert-type device. The results indicated that the catalytic MoS2 as a single phase was uniformly distributed in the matrix. However, the doping of MoO2 introduced O2− ions, which combined with Mg and Ce to form MgO and CeO2 phases, respectively. The MoS2-catalyzed alloy exhibited faster hydrogen absorption and desorption rates, which could absorb 4.5 wt % H2 in 120 s (at 573 K) and release 3 wt % H2 in 330 s (at 633 K). The initial dehydrogenation temperatures of the MoS2- and MoO2-catalyzed alloys were 467.7 and 475.7 K, respectively. The dehydrogenation activation energy of MoS2- and MoO2-catalyzed alloys were 103.7 and 110.2 kJ mol−1 respectively. Addition of MoO2 and MoS2 modified the decomposition enthalpy and entropy values, but these changes were very limited. Generally, S2− was superior to O2− ions in enhancing the hydrogen storage properties of the alloy.

Impacts of Ce dopants on the hydrogen storage performance of Ti-Cr-V alloys

Vanadium-based alloys are considered to be one of the most promising hydrogen storage materials due to their high hydrogen storage capacity under ambient conditions. However, their complex activation at high temperature and poor stability pose serious challenges for large-scale applications. In this work, a series of TiCr3V16Cex (x = 0, 0.1, 0.2, 0.4, 1) hydrogen storage alloys were developed with different Ce contents using arc melting. The hydrogen storage and desorption performance, activation mechanism, and hydrogen absorption mechanism of the prepared alloys were investigated. Physical characterization confirms that the alloy is body-centered cubic (BCC) with Ce dopants, which exist in the form of oxides. The pressure-composition-temperature (PCT) test showed that the hydrogen storage plateau pressure of the Ce-doped alloy is increased compared to the Ce-free counterparts, while the hydrogen storage capacity decreased slightly with increasing Ce content. In addition, the influence of Ce doping on the alloy kinetics and thermodynamics is also discussed. The results showed that the TiCr3V16Cex (x = 0.2, 0.4, 1) alloys could absorb and release hydrogen at room temperature without activation. As an optimum, the TiCr3V16Ce0.2 alloy shows a hydrogen absorption rate of up to 3.69 wt%, and an effective hydrogen desorption capacity of 2.29 wt% at 25 °C. After hydrogen absorption and desorption cycles, the alloy almost maintains its original capacity. The Ce-doped BCC alloy developed in this work provides a new route to achieve high hydrogen storage performance under mild conditions.

Microstructural features and improved reversible hydrogen storage properties of ZrTiVFe high-entropy alloy via Cu alloying

ZrTiVFe high-entropy alloy has shown desirable hydrogen absorption and desorption properties due to its lattice distortion effect and high content of C14 phase that can store hydrogen. In this study, element Cu was used to improve the reversible hydrogen storage properties of equimolar ZrTiVFe alloy by increasing valence-electron concentration (VEC), and (ZrTiVFe)1-xCux (x = 0.05, 0.1, 0.2) alloys were prepared. After studying their microstructural features and hydrogen storage properties, the results indicate that (ZrTiVFe)0.95Cu0.05 and (ZrTiVFe)0.90Cu0.10 alloys are mainly consisted of C14 Laves phase and a small amount of α-Ti and α-Zr phases. When the Cu content increases to 20 at. %, the microstructure transforms to reticular ZrTiCu2 phase around C14 Laves phase, and the Cu8Zr3 phase is formed in final solidification stage. The fastest hydrogen absorption rate of (ZrTiVFe)0.80Cu0.20 alloy at room temperature suggests the ZrTiCu2 and Cu8Zr3 phases can provide preferential paths for hydrogen atoms diffusion. The amount of hydrogen in (ZrTiVFe)0.90Cu0.10 hydride that cannot be desorbed at 400 °C in vacuum is greatly reduced from 0.370 wt% to 0.084 wt% comparing with ZrTiVFe hydride. The addition of element Cu reduces the stability of ZrTiVFe hydride significantly, which favors the hydrogen desorption of the (ZrTiVFe)1-xCux alloys.

Effect of yttrium content on microstructure and hydrogen storage properties of TiFe-based alloy

In this paper, the experimental alloy with the standard composition of Ti1.1-xZr0.1YxFe0.6Ni0.3Mn0.2 (x = 0–0.08) was synthesized by vacuum induction melting. The activation properties and hydrogen absorption/desorption kinetics were significantly improved by adding different amounts levels of rare earth elements Y to partially replace Ti in TiFe alloys. The microstructure, phase composition and hydrogen storage properties of the alloy before and after hydrogen absorption/desorption were characterized and tested by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and Sieverts-type manual PCT hydrogen storage tester. The experimental results show that the as-cast alloy consists of Ni-rich TiFe main phase, a small amount of ZrMn2 phase biased on the TiFe phase and Y-rich phase. The addition of Y significantly increases the phase boundary and refines the crystallization, and significantly shortens the activation incubation period of the cast alloy. The alloy requires only the first hydrogen absorption to fully achieve activation at 150 °C, and still exhibits a fast hydrogen absorption rate at −10 °C. Meanwhile, When the Y content is 0.02, the saturation rate (R100a) of hydrogen absorption reaches 92%, and the maximum hydrogen absorption capacity is 1.704 wt% at 70 °C. And the absolute values of the enthalpy and entropy changes of hydrogen absorption/desorption increase with the increasing of Y content.

Improved hydrogen storage properties of Li-Mg-N-H system by lithium vanadium oxides

The Mg(NH2)2-2LiH system is considered as one of the most potential hydrogen storage materials due to its high hydrogen storage capacity (5.6 wt%) and excellent reversible hydrogen adsorption and desorption performance. However, its poor kinetic characteristics of hydrogen absorption and desorption limit its practical application. In this work, Li3VO4 @LiVO2 was synthesized by a hydrothermal method, and was then introduced into Mg(NH2)2-2LiH system to enhance the hydrogen absorption and desorption kinetic characteristics. The results show that the hydrogen storage properties were greatly improved with addition of 10 wt% Li3VO4 @LiVO2 addition. As for the hydrogen absorption and desorption kinetics, the average hydrogen absorption rate of 10 wt% Li3VO4 @LiVO2 modified Li-Mg-N-H sample within 20 min at 200 ℃ increased by 95.2% compared with that of the pristine Li-Mg-N-H sample, and the average hydrogen desorption rate of 10 wt% Li3VO4 @LiVO2 modified sample within 30 min at 180 ℃ increased by 42% compared with that of the pristine sample. The Ea of hydrogen desorption decreased from 117.86 kJ/mol to 99.43 kJ/mol, which also indicates that Li3VO4 @LiVO2 catalyst effectively improved the kinetic performance of hydrogen desorption and desorption of Li-Mg-N-H. Moreover, the hydrogen desorption capacity and hydrogen absorption capacity of 10 wt% Li3VO4 @LiVO2 modified Li-Mg-N-H increased by 18.4% and 13.8% compared with that of the pristine sample. The catalytic mechanism of Li3VO4 @LiVO2was discussed based on XRD, XPS and FTIR analysis results.

Enhanced de-/hydrogenation kinetics of a hyper-eutectic Mg85Ni15-Ag alloy facilitated by Ag dissolving in Mg2Ni

In order to accelerate the hydrogen absorption and desorption rates of hyper-eutectic Mg-Ni alloy, Mg 85 Ni 15- x Ag x ( x = 0, 0.2, 0.4, 0.6) alloys were prepared and the results show that fishbone eutectic was formed without change of phase composition. It was found that Ag atoms were dissolved in fishbone eutectic Mg 2 Ni and the average cell parameters of Mg 2 Ni increase with the increase of Ag content. Owing to adjusting lattice parameters, the hydrogen absorption and desorption rates of Mg 85 Ni 14.8 Ag 0.2 alloy are significantly improved. About 4.47 wt% hydrogen is absorbed at 275 ℃ only in 1 min, with the maximum capacity of 5.84 wt% in 60 min. The Mg 85 Ni 15- x Ag x ( x = 0.2, 0.4, 0.6) hydrides can be completely dehydrogenated within 10 min at 275 ℃. The corresponding activation energies for dehydrogenation are determined to be 80.4, 97.1 and 97.8 kJ/mol, respectively, which are lower than 117.8 kJ/mol of Mg 85 Ni 15 . The onset dehydrogenation temperature of Mg 85 Ni 14.8 Ag 0.2 hydride is reduced to 201 ℃, which is much lower than 220 ℃ of the Mg 85 Ni 15 hydride. The dissolving of Ag in Mg 2 Ni leads to a lattice expansion, which facilitates the diffusion for hydrogen atoms and decrease the energy barrier required for nucleation of Mg/Mg 2 Ni. As a result, the hydrogen de-/absorption rates were obvious accelerated and the onset dehydrogenation temperature was decreased. • The lattice size of Mg2Ni was regulated by doping Ag. • Hydrogen storage capacity of Mg85Ni14.8Ag0.2 alloy reaches 5.84 wt% at 275 ℃. • The Ea value for decomposition of Mg85Ni14.8Ag0.2 hydride decreases to 80.4 kJ/mol. • Addition of Ag reduces the initial desorption temperature of Mg85Ni15 hydrides.

Effect of Mn substitution on the structure and hydrogen storage properties of La0.75Ce0.25Ni5-xMnx alloy

Abstract In this study, La0.75Ce0.25Ni5-xMnx (x = 0, 0.1, 0.2, 0.3) alloys were prepared by vacuum arc melting. The effect of the addition of Mn on the alloy microstructure and hydrogen absorption/desorption properties were explored by characterizing X-ray diffraction (XRD), scanning electron microscopy (SEM), laser particle size test, hydrogen absorption kinetic test, and P-C-T test. The XRD results show that the series of alloys are single-phase alloys composed of the LaNi5 phase, and the cell volume of the alloy gradually increases as the amount of Mn replacing Ni increases. The P-C-T curve of the alloy shows that the alloy has obvious hydrogen absorption/desorption plateau regions, which gradually decrease with increasing Mn content, while the hydrogen storage capacity remains unchanged. The hydrogen absorption kinetic curve of the alloy was tested, and it was found that the hydrogen absorption rate of the alloy increased with the increase of Mn content. These studies show that doping the Mn element in the La0.75Ce0.25Ni5-xMnx (x = 0, 0.1, 0.2, 0.3) alloys may regulate plateau pressure without affecting the hydrogen storage capacity or kinetics properties, providing a reference for the application of this type of alloy in hydrogen pressurization, purification, etc.

Adoption of triply periodic minimal surface structure for effective metal hydride-based hydrogen storage

Metal hydrides (MHs) are highly effective for storing hydrogen because of their stability, relatively low temperature and pressure, and high volumetric hydrogen density. However, their gravimetric density is low because of the weights of the MHs, leading to a low potential for mobility applications unless the reactor also acts as a body frame, thereby compensating for the light weight. Triply periodic minimal surface (TPMS) structures show great potential as heat exchangers (HEs) with extended surface properties per volume and reinforced structures designed to bear mechanical loads. Therefore, these structures are considered promising for application as hydrogen carriers, especially in MH-based hydrogen storage. This study aims to develop MH-based hydrogen storage using a TPMS structure. Furthermore, a mathematical model was developed to analyze and improve its performance in terms of the hydrogen absorption and desorption rates. The analysis using the mathematical model was validated with existing experimental data. Different cooling conditions were compared with natural convection. Moreover, finite element analysis was applied to evaluate the capability of the current structure design in withstanding the working pressure and load. This study's important finding is that the propose structure is proven to have higher hydrogen storage performance, including density and hydrogen charging and discharging performances. In addition, it is also found that improving the cooling conditions could increase the absorption rate. Forced convection (with a heat-transfer coefficient of 500 W/m2·K) seems to be a preferable cooling solution that requires low energy consumption and provides sufficient cooling. By using this cooling condition with the proposed TPMS reactor design, 90% of hydrogen is absorbed within 2000 s. Natural cooling requires almost double that time. It was also found that a reactor with a TPMS structure with a 1 mm wall thickness design could withstand MH working pressure conditions and a compression load of 5000 N. Based on this finding, the TPMS-based structure can be considered as a promising novel way of storing hydrogen for mobility applications.

Multi-variable optimization of metal hydride hydrogen storage reactor with gradient porosity metal foam and evaluation of comprehensive performance

Hydrogen storage performance for metal hydride (MH) reactor is restricted by the poor thermal conductivity of MH. In this study, the gradient porosity metal foam was added into MH reactor for enhancing heat transportation (GMF reactor), and its hydrogen absorption performance was investigated numerically in detail. Then, thermal resistance analysis was conducted to analyze the heat transportation in GMF reactor, and Genetic Algorithm was applied for optimizing metal foam distribution under different conditions. It was indicated that the hydrogenation performance for optimized two-layer GMF reactor was increased by 11.5% compared with uniform metal foam reactor (UMF reactor). The optimization results indicated that the optimal volumetric fractions of metal foam (VFMF) are about 0.08 for both optimized GMF reactor and UMF reactor with the trade-off of hydrogen storage capacity and hydrogen absorption rate. Then, a new indicator of comprehensive hydrogen storage performance (CHSP) for MH reactor was proposed, which includes the influence of hydrogen storage rate, hydrogen storage capacity, volumetric storage density and gravimetric storage density. Besides, the hydrogenation performance for optimized GMF reactor was improved with metal foam layer increasing, and the optimal porosity distribution was gradually approaching a specific power exponent trend. It was showed that the hydrogenation performance for power-exponent GMF reactor was increased by 2.8% and 18.2% compared with that of optimized four-layer GMF reactor and UMF reactor, respectively.

Hydrogenation behavior of Cr-coated laser beam welds of E110 zirconium alloy

The influence of chromium coating on hydrogenation behavior of laser beam welds (LBW) of E110 zirconium alloy was studied at 360–900 °C and hydrogen pressure of 2 bar. The deposition of Cr coating can slow down hydrogen absorption rate of the LBW samples as activation energy for hydrogen absorption (70 kJ/mol) is higher compared to uncoated ones (61 kJ/mol). The growth of hydrides depends on the hydrogenation conditions and original microstructure of welded alloy in different zones. Nanoindentation and three-point bending tests show that hydride precipitations can cause hardening of LBW E110 alloy samples and loss of its plasticity. Some additional aspects of applying Cr coatings for protection of LBW Zr alloy in hydrogen atmosphere are presented.

Design optimization of a magnesium-based metal hydride hydrogen energy storage system

Metal hydrides (MH) are known as one of the most suitable material groups for hydrogen energy storage because of their large hydrogen storage capacity, low operating pressure, and high safety. However, their slow hydrogen absorption kinetics significantly decreases storage performance. Faster heat removal from MH storage can play an essential role to enhance its hydrogen absorption rate, resulting in better storage performance. In this regard, the present study aims to improve heat transfer performance to positively impact the hydrogen absorption rate of MH storage systems. A novel semi-cylindrical coil is first designed and optimized for hydrogen storage and embedded as an internal heat exchanger with air as the heat transfer fluid (HTF). The effect of novel heat exchanger configurations is analyzed and compared with normal helical coil geometry, based on various pitch sizes. Furthermore, the operating parameters of MH storage and HTF are numerically investigated to obtain optimal values. ANSYS Fluent 2020 R2 is utilized for the numerical simulations. Results from this study demonstrate that MH storage performance is significantly improved by using a semi-cylindrical coil heat exchanger (SCHE). The hydrogen absorption duration reduces by 59% compared to a normal helical coil heat exchanger. The lowest coil pitch from SCHE leads to a 61% reduction of the absorption time. In terms of operating parameters for the MH storage with SCHE, all selected parameters provide a major improvement in the hydrogen absorption process, especially the inlet temperature of the HTF.

Hydrogen interaction with Mn-doped Zr2Fe (101) surface: A DFT study

The metal getter materials play a pivotal role in the treatment of tritium-containing waste gas, which is one of the most important tasks in fusion reactions, owing to the characteristics of no tritiated water product and easy recovery by the form of reversible metal hydrides. As the most promising and attractive hydrogen isotopes trapping materials for metal getters, Zr2Fe alloy has the advantages of low thermal neutron absorption, high corrosion resistance, fast hydrogen absorption rate, and high absorption efficiency, which have attracted great attention. Though pristine/Mn-doped Zr2Fe have been widely used to trap tritium from nitrogen and inert gases, an atomic-scale description of the inherent interaction mechanism between hydrogen and pristine/Mn-doped Zr2Fe surface is still lacking. Herein, density functional theory (DFT) calculations were employed to study the effect of doping Mn on the adsorption, dissociation and diffusion of hydrogen on the Zr2Fe(101) surface. It is found that the number of adsorption sites and adsorption strength of hydrogen increase when a Fe atom is substituted by a Mn atom. In addition, the dissociation and diffusion barriers of hydrogen are lowered on the Mn-doped surface. The electronic structure analysis shows that the adsorptions of hydrogen molecules cause more electron transfer to the surfaces and there exists strong interaction between hydrogen and doping Mn. Consequently, this should enhance the hydrogen storage performance of Zr2Fe alloy, due to the surface adsorption and diffusion of hydrogen being improved by doping Mn. All these findings can provide insightful guidance for future research to improve the hydrogen storage capacity of Zr-based alloy materials and the design of metal getters for tritium-containing waste gas treatment.

Corrosion-induced hydrogen evolution, absorption, and cracking behaviors of ultra-high-strength galvanized and galvannealed steel sheets

Various experimental analyses on hydrogen evolution, absorption, and cracking behaviors were conducted to gain a fundamental understanding of the hydrogen embrittlement of ultrastrong steel sheets with galvanized (GI) and galvannealed (GA) coatings. The hydrogen evolution and absorption behaviors are controlled primarily by the potential differences between the coating and exposed steel substrate, and the corrosion-induced damage pattern of the coating. The higher absorption rate of hydrogen was more pronounced in corroded GI-coated steel caused by the larger cathodic polarization applied to the exposed substrate, and a more severe form of coating dissolution by aqueous corrosion in a 3.5% NaCl + 0.3% NH4SN solution. In contrast, the corrosive species can only penetrate through the pre-existing cracks in the brittle Fe-Zn intermetallic phases composed of the GA coating, and the driving force for hydrogen evolution becomes smaller. These result in significant differences in hydrogen penetration and cracking behaviors between the two coated ultrastrong steels.

Synthesis of low-cost biomass charcoal-based Ni nanocatalyst and evaluation of their kinetic enhancement of MgH2

In this study, a low-cost biomass charcoal (BC)-based nickel catalyst (Ni/BC) was introduced into the MgH 2 system by ball-milling. The study demonstrated that the Ni/BC catalyst significantly improved the hydrogen desorption and absorption kinetics of MgH 2 . The MgH 2 + 10 wt% Ni/BC-3 composite starts to release hydrogen at 187.8 °C, which is 162.2 °C lower than the initial dehydrogenation temperature of pure MgH 2 . Besides, 6.04 wt% dehydrogenation can be achieved within 3.5 min at 300 °C. After the dehydrogenation is completed, MgH 2 + 10 wt% Ni/BC-3 can start to absorb hydrogen even at 30 °C, which achieved the absorption of 5 wt% H 2 in 60 min under the condition of 3 MPa hydrogen pressure and 125 °C. The apparent activation energies of dehydrogenation and hydrogen absorption of MgH 2 + 10 wt% Ni/BC-3 composites were 82.49 kJ/mol and 23.87 kJ/mol lower than those of pure MgH 2 , respectively, which indicated that the carbon layer wrapped around MgH 2 effectively improved the cycle stability of hydrogen storage materials. Moreover, MgH 2 + 10 wt% Ni/BC-3 can still maintain 99% hydrogen storage capacity after 20 cycles. XRD, EDS, SEM and TEM revealed that the Ni/BC catalyst evenly distributed around MgH 2 formed Mg 2 Ni/Mg 2 NiH 4 in situ, which act as a “hydrogen pump” to boost the diffusion of hydrogen along with the Mg/MgH 2 interface. Meanwhile, the carbon layer with fantastic conductivity enormously accelerated the electron transfer. Consequently, there is no denying that the synergistic effect extremely facilitated the hydrogen absorption and desorption kinetic performance of MgH 2 . The carbon layer is evenly wrapped around MgH 2 /Mg, and Ni nano catalyst is evenly distributed on the surface. During dehydrogenation and reabsorption, Ni nanoparticles generate Mg 2 Ni and Mg 2 NiH 4 in situ. The use of uniformly distributed Mg 2 Ni/Mg 2 NiH 4 as a “hydrogen pump” promotes the diffusion of hydrogen along the Mg/MgH 2 interface, and the carbon layer with good conductivity accelerates the electron transfer. It is believed that the synergistic effect of the two improves the hydrogen absorption and desorption rate of MgH 2 . • Biomass charcoal was introduced into the MgH 2 system for the first time. • Composites started to release H 2 at 187.8 °C and could start to absorb H 2 at 30 °C. • The activation energy of de/hydrogenation was significantly reduced for composites. • Biomass charcoal contributes to the cyclic stability of composites.

Hydrogen storage performance of LaNi3.95Al0.75Co0.3 alloy with different preparation methods

Rare-earth AB5-type La–Ni–Al hydrogen storage alloys are widely studied due to their extensive application potentials in hydrogen isotope storage, hydrogen isotope isolation and hydrogen compressors, etc. Good hydriding/dehydriding kinetics, easily activation, high reversibility are important factors for their practical application. However, their overall hydrogen storage performance, especially plateau pressure and hydrogen absorption/desorption durability need to be further optimized. In this study, the microstructures and the hydrogen storage properties of as-cast, annealed, and melt-spun LaNi3.95Al0.75Co0.3 alloys were investigated. The experimental results of XRD and SEM showed that all alloys contained a pure CaCu5 type hexagonal structure LaNi4Al phase. The cell volume increased in an order of annealed ​> ​melt-spun ​> ​as-cast, resulting in a lower hydrogen absorption/desorption plateau pressure and a more stable hydride phase. The hydrogen storage capacity of three alloys was almost the same. The slope factor of the annealed and melt-spun alloys is smaller than the as-cast alloy, indicating that heat-treatment process can make the alloys more uniform. For the cycle stability of the alloys, the hydrogen absorption rate of the annealed alloy and melt-spun alloy was much faster than that of the as-cast alloy after 500 cycles. The melt-spun alloy showed high pulverization resistance during hydrogen absorption/desorption, and exhibited an excellent cycling retention of 99% after 500 cycles, suggesting that melt-spinning process can enhance the cycle stability and improve the cycle life of the alloy.