Improved Hydrogen Storage Properties Research Articles

Enhancing the dehydrogenation properties of LiAlH4 through the addition of ZrF4 for solid-state hydrogen storage

Hydrogen energy is emerging as an essential alternative to fossil fuels due to its clean energy profile, generating energy without greenhouse gas emissions. Solid-state hydrogen storage, particularly using complex hydrides like LiAlH4, holds promise due to high hydrogen capacities. However, practical applications of LiAlH4 face obstacles due to slow dehydrogenation kinetics and high decomposition temperatures. This study investigates the catalytic effect of ZrF4 on LiAlH4 to improve hydrogen storage properties. Incorporating 10 wt% ZrF4 has significantly lowered the onset desorption temperature from 160 °C to 80 °C. Desoption kinetic result showed that the addition of 10 wt% ZrF4 can enables the release of 5.6 wt% hydrogen in 120 min at 100 °C, which is 50 times faster than in undoped samples. X-ray diffraction analysis indicated that ZrF4 facilitated the in-situ formation of Al3Zr and LiF phases during dehydrogenation, thereby enhancing catalytic efficiency. The desorption activation energies for first two reactions decreased significantly by ∼ 16 kJ/mol and ∼24 kJ/mol with ZrF4 doping. These findings suggest that ZrF4 effectively improves the hydrogen storage properties of LiAlH4, positioning it as a potential catalyst for solid-state hydrogen storage systems.

Facilitated hydrogen storage properties of MgH2 by Ni nanoparticles anchored on Mo2C@C nanosheets

Magnesium hydride (MgH2) holds promise as a hydrogen storage material, but its practical application is impeded by high desorption temperatures and slow kinetics, presenting substantial challenges. Herein, an efficient approach is proposed to synthesize Mo2C@C nanosheets-supported Ni nanoparticles (Ni/Mo2C@C-2) materials, which can operate as a highly efficient catalyst to enhance hydrogen desorption of MgH2. The ball-milled MgH2–7.5 wt% Ni/Mo2C@C-2 demonstrates prominent hydrogen desorption kinetics with an activation energy (Ea) of 97.22 kJ mol−1, alongside remarkable cycling stability, maintaining a capacity retention of 97.8% after 20 cycles. Consequently, the results reveal that the improvement of hydrogen storage properties for MgH2 can be attributed to the synergistic effect of the in-situ generated Mg2NiH4 with highly dispersion, the sustained Mo2C nanosheets, and highly graphitized carbon. This work provides a reliable strategy for constructing polyoxometalates derivatives to facilitate the hydrogen desorption and cycling of MgH2.

Effect of Ce0.6Zr0.4O2 nanocrystals on boosting hydrogen storage performance of MgH2

Magnesium hydride (MgH2) has been widely recognized as a highly promising solid-state media for hydrogen storage. However, the high operating temperature and the intrinsic sluggish kinetics hinder the practical application as a portable solid storage carrier. To address this issue, we have successfully fabricated a novel rare earth-containing bimetallic oxide additive, namely Ce0.6Zr0.4O2 nanocrystals, which exhibits a significant catalytic effect in enhancing the hydrogen storage properties of MgH2. By incorporating 7 wt% Ce0.6Zr0.4O2 into MgH2, the modified composite releases hydrogen as low as 201 °C. Furthermore, in an isothermal dehydrogenation test conducted at 270 °C for 8 min, approximately 6.15 wt% of H2 was desorbed. The composites can rapidly recharge hydrogen at a low temperature of 50 °C and 6.02 wt% H2 being absorbed within 3 min at 150 °C under 50.0 bar. Comparatively, the dehydrogenation activation energy of the Ce0.6Zr0.4O2-modified MgH2 significantly decreased compared to MgH2 by ball milling. In addition to its improved hydrogen storage properties, the composite also exhibits excellent cycling stability. Through cyclic de-/rehydrogenation experiments conducted at 270 °C, a capacity retention of 98.9 % was achieved over 20 cycles. This exceptional performance can be attributed to the in-situ formation of the CeH2.73/CeO2-x and ZrO2, which originated from the Ce0.6Zr0.4O2 additive following the first de-/rehydrogenation cycle. The uniform dispersion of the multiphase component nano-sized active species within the MgH2 matrix facilitates charge transfer and accelerates hydrogen diffusion. Density functional theory calculations revealed the dissociation energy barrier and dissociation energy of H2 were alleviated by integrating Zr into CeO2. This work provides valuable insights for further rational designs of novel catalysts by transition metals and rare earths in promoting the commercialization of MgH2.

Microstructure and hydrogen storage properties of magnesium–gallium binary alloys

In this paper, gallium was used as alloying element to improve hydrogen storage properties of magnesium. Therefore, Mg–x wt% Ga (x = 5, 10, 25, 50) binary alloys were prepared by induction melting method. The microstructure and phase composition of Mg–Ga alloy were analyzed using X-ray diffractometer and scanning electron microscope. The results show that Mg–Ga binary alloys consist of Mg and Mg5Ga2 phases. The Mg and Mg5Ga2 react with H2 to form Mg2Ga and MgH2 during hydrogenation process. The hydrogen storage kinetics and thermodynamic properties of the alloys were tested using a Sieverts-type apparatus. It is found that the dehydrogenation rates of the samples increase with increasing gallium content, and they are all better than pure magnesium. Thermal analysis results indicate that increasing gallium content decreases dehydrogenation temperature of Mg–Ga alloy. The beneficial effects of adding gallium in magnesium is that interfaces and secondary phase resulted from alloying can promote the hydrogen desorption process of the alloy. The Mg–50 wt% Ga alloy has the lowest dehydrogenation activation energy. However, increasing gallium content inevitably reduces the hydrogen storage capacity of the Mg–Ga alloys. Furthermore, alloying with gallium does not change the thermomechanical properties of magnesium.

Lithium Borohydride Nanorods: Self-Assembling Growth and Remarkable Hydrogen Cycling Properties.

Nanostructured metal hydrides with unique morphology and improved hydrogen storage properties have attracted intense interests. However, the study of the growth process of highly active borohydrides remains challenging. Herein, for the first time the synthesis of LiBH4 nanorods through a hydrogen-assisted one-pot solvothermal reaction is reported. Reaction of n-butyl lithium with triethylamine borane in n-hexane under 50bar of H2 at 40-100°C gives rise to the formation of the [100]-oriented LiBH4 nanorods with 500-800nm in diameter, whose growth is driven by orientated attachment and ligand adsorption. The unique morphology enables the LiBH4 nanorods to release hydrogen from ≈184°C, 94°C lower than the commercial sample (≈278°C). Hydrogen release amounts to 13wt% within 40min at 450°C with a stable cyclability, remarkably superior to the commercial LiBH4 (≈9.1wt%). More importantly, up to 180°C reduction in the onset temperature of hydrogenation is successfully attained by the nanorod sample with respect to the commercial counterpart. The LiBH4 nanorods show no foaming during dehydrogenation, which improves the hydrogen cycling performance. The new approach will shed light on the preparation of nanostructured metal borohydrides as advanced functional materials.

Hybrid of bulk NbC and layered Nb4C3 MXene for tailoring the hydrogen storage kinetics and reversibility of Li–Mg–B–H composite: An experimental and theoretical study

The Li-Mg-B-H composite (2LiBH4 + MgH2) is acknowledged as a promising material for hydrogen storage due to its large hydrogen capacity (11.4 wt.%). However, the sluggish kinetics and poor reversibility make it difficult to be practically used. In this work, the hydrogen storage performances of 2LiBH4 + MgH2 have been significantly improved by a hybrid of bulk NbC and layered Nb4C3 MXene (denoted as “Nb–C”). The 2LiBH4 + MgH2 + 6 wt.% Nb–C can release 8.5 wt.% H2 within 30 min at 400 °C and the dehydrogenated composite can absorb 9.3 wt.% H2 within 30 min at 350 °C and 7.5 MPa H2. The reversible dehydrogenation capacity maintains at 8.4 wt.% after 24 cycles, with a capacity retention ratio of 95.4 %. By contrast, the undoped 2LiBH4 + MgH2 suffers from serious capacity degradation, with the capacity decreased dramatically to 3.5 wt.% after 3 cycles. Microstructural studies revealed that the doped composite has uniform particle and elemental distributions and possesses various multiphase interfaces of LiH/MgB2/NbC/Nb4C3, which is beneficial to hydrogen diffusion during the hydrogen uptake and release process. Theoretical studies by first principle calculation presented an extended bond length of the Mg–H and B–H bonds in the 2LiBH4 + MgH2 + NbC system, which may also explain the improved hydrogen storage properties of 2LiBH4 + MgH2 by addition of Nb-C. This work provides new insights into the role of transition metal carbides in regulating the Li–Mg–B–H hydrogen storage materials both experimentally and theoretically.

Microstructure and hydrogen storage properties of the Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) alloys

Rare earth elements have excellent catalytic effects on improving hydrogen storage properties of the Mg2Ni-based alloys. This study used a small amount of Y to substitute Mg partially in Mg2Ni0.9Co0.1 and characterized and discussed the effects of Y on the solidification and de-/hydrogenation behaviors. The Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) hydrogen storage alloys were prepared using a metallurgy method. The phase composition of the alloys was studied using X-ray diffraction (XRD). Additionally, their microstructure and chemical composition were studied using scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. The hydrogen absorption and desorption properties of the alloys were studied using pressure-composition isotherms and differential scanning calorimetric (DSC) measurements. The structure of the as-cast Mg2Ni0.9Co0.1 alloy was composed of the peritectic Mg2Ni, eutectic Mg–Mg2Ni, and a small amount of pre-precipitated Mg–Ni–Co ternary phases, and was converted into the Mg2NiH4, Mg2Ni0.9Co0.1H4, and MgH2 phases after hydrogen absorption. Furthermore, the XRD patterns of the alloys showed the MgYNi4 phase and a trace amount of the Y2O3 phase along with the Mg and Mg2Ni phases after the addition of Y. After hydrogen absorption, the phase of the alloys was composed of the Mg2NiH4, MgH2, MgYNi4, YH3, Y2O3, and Mg2NiH0.3 phases. With the increase of Y addition, the area ratios of the peritectic Mg2Ni matrix phase in the Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) alloys gradually decreased until they disappeared. However, the eutectic structure gradually increased, and the microstructures of the alloys were obviously refined. The addition of Y improves the activation performance of the alloys. The alloy only needed one cycle of de-/hydrogenation to complete the activation for x = 0.4. The DSC curves showed that the initial dehydrogenation temperatures of Mg2Ni0.9Co0.1 and Mg1.8Y0.2Ni0.9Co0.1 were 200 and 156 °C, respectively. The desorption activation energies of the hydrides of the Mg2Ni0.9Co0.1 and Mg1.8Y0.2Ni0.9Co0.1 alloys calculated using the Kissinger method were 94.7 and 56.5 kJ/mol, respectively. Moreover, the addition of Y reduced the initial desorption temperature of the alloys and improved their kinetic properties.

Investigation of hydrogen storage properties for high entropy alloys (Ti30V30Cr30Fe10 and Ti40V30Cr10Fe10Al10)

The broad compositional space of high entropy alloys (HEAs) presents an opportunity to research new hydrogen storage materials, with improved hydrogen storage properties under ambient temperature and pressure. The properties of these materials are influenced by several factors including composition, operating pressure, and temperature, as well as the fabrication techniques employed. As such this study investigated two HEAs, namely Ti30V30Cr30Fe10 and Ti40V30Cr10Fe10Al10 using empirical and thermodynamic modelling methods, where Ti30V30Cr30Fe10 was successfully synthesized using LENS. The phase prediction criterion showed formation of a single solid BCC structure with VEC ≤ 5.4 and XRD confirmed formation of BCC and Laves phase structure. The investigated HEAs demonstrated excellent performance for hydrogen storage with maximum hydrogen storage capacities of about 3.8 and 4 wt% respectively at 25 and 100 0C, exceeding the previously reported HEAs for hydrogen storage.

Development of AB2-type TiZrCrMnFeCoV intermetallic high-entropy alloy for reversible room-temperature hydrogen storage

Intermetallic high-entropy alloys (HEAs) with C14 Laves phase structure have shown promise as hydrogen storage materials due to their ability to maintain the advantages of the AB2-type hydrogen storage alloys while offering the potential for the improvement of hydrogen storage properties through the use of multi-principal elements. However, some intermetallic HEAs are limited in their ability to scale-up production using the low-cost induction melting method and reversible hydrogen storage at room temperature due to their extremely low equilibrium desorption pressure. In this work, intermetallic HEAs with reversible room-temperature hydrogen storage are designed using an empirical model based on calculation of the electronic and geometrical factors. An orthogonal experiment was conducted to optimize the composition and the optimal (Ti1.3Zr0.7)1.1Cr1.1Mn1.8Fe0.3Co0.4V0.4 HEA with a single C14 Laves phase was found to exhibit the best overall hydrogen performance. It can reversibly store 1.84 wt% hydrogen with a relatively low plateau hysteresis factor (0.71) and slope factor (0.89) at a temperature of 15 °C. The dehydrogenation enthalpy and entropy of the optimal HEA were determined to be 35.0 kJ mol−1 and 115.3 J mol−1 K−1, respectively. To reduce the cost of HEAs, FeV80 was employed to replace the V. It was found that the optimal HEA could be successfully scaled-up for production, and our findings demonstrate the potential of intermetallic HEAs for efficient hydrogen storage.

Enhanced hydrogen sorption properties of uniformly dispersed Pd-decorated three-dimensional (3D) Mg@Pd architecture

This study demonstrates the hydrogen sorption improvement of Mg through the three-dimensional decoration of a noble catalyst. An Mg@Pd composite was synthesized by decorating Pd nanoparticles onto the Mg matrix via a facile solid-gas reduction method. Electron tomography analysis confirms the formation of a three-dimensional (3D) architecture of the Mg@Pd particulate composite. The Mg@Pd composite shows excellent hydrogenation/dehydrogenation kinetics even at low temperatures as compared to a catalyst-free Mg sample. Moreover, the hydrogenated Mg@Pd composite can desorb hydrogen at as low as 246 °C that is 87 °C lower than that of the pure MgH2. Hydrogenation of the Mg@Pd composite leads to the development of a multiphase system consisted of PdH0.706, MgPd and MgH2 whereas dehydrogenation occurred via two simultaneous desorption reactions results in Mg6Pd and Mg phases. The uniform dispersion of Pd nanoparticles on the surface of the 3D Mg matrix has provided with fast catalytic interfaces via the hydrogen “spillover” mechanism while the concomitant hydrogen diffusion processes are enhanced by the “hydrogen pump” effect of PdH0.706/MgPd interfaces. Furthermore, the low temperature hydrogen sorption performances of the Mg@Pd composite can be attributed to the interphase reversibility between MgPd and Mg6Pd leading to the thermodynamic destabilization of MgH2. This study suggests that strategically new approaches can govern significant improvements in hydrogen storage properties of Mg-based systems.

Improved hydrogen storage properties of MgH2 by Mxene (Ti3C2) supported MnO2

MgH2 is a promising high-capacity solid hydrogen storage material. In this work, MnO2-doped Ti3C2 (Ti3C2@MnO2) was synthesized and used as a catalyst to improve the hydrogen storage performance of MgH2. We found that the dehydrogenated 10 wt% Ti3C2@MnO2-doped MgH2 sample exhibited good hydrogen adsorption ability even at room temperature (30 °C), and could absorb 5.13 wt% of hydrogen in 400 s at 75 °C. The re‑hydrogenated Ti3C2@MnO2-doped MgH2 sample started to release hydrogen at 182 °C and required 484 s to completely release hydrogen at 275 °C with a dehydrogenation capacity of 6.4 wt%. The Ti3C2@MnO2 composite did not change the thermodynamic properties of MgH2. In the MgH2 + Ti3C2@MnO2 sample, Ti3C2, TiO2, MnO2, MnO, and Mn combined with MgH2 to form Ti3C2/MgH2, TiO2/MgH2, MnO2/MgH2, MnO/MgH2, and Mn/MgH2 multiphase interfaces, which improved the hydrogen storage performance of MgH2. The findings of this work may provide a new strategy for preparing novel and efficient catalysts for hydrogen storage applications.

Nanoparticulate ZrNi: In Situ Disproportionation Effectively Enhances Hydrogen Cycling of MgH2.

High thermal stability and sluggish absorption/desorption kinetics are still important limitations for using magnesium hydride (MgH2) as a solid-state hydrogen storage medium. One of the most effective solutions in improving hydrogen storage properties of MgH2 is to introduce a suitable catalyst. Herein, a novel nanoparticulate ZrNi with 10-60 nm in size was successfully prepared by co-precipitation followed by a molten-salt reduction process. The 7 wt % nano-ZrNi-catalyzed MgH2 composite desorbs 6.1 wt % hydrogen starting from ∼178 °C after activation, lowered by 99 °C relative to the pristine MgH2 (∼277 °C). The dehydrided sample rapidly absorbs ∼5.5 wt % H2 when operating at 150 °C for 8 min. The remarkably improved hydrogen storage properties are reasonably ascribed to the in situ formation of ZrH2, ZrNi2, and Mg2NiH4 caused by the disproportionation reaction of nano-ZrNi during the first de-/hydrogenation cycle. These catalytic active species are uniformly dispersed in the MgH2 matrix, thus creating a multielement, multiphase, and multivalent environment, which not only largely favors the breaking and rebonding of H-H bonds and the transfer of electrons between H- and Mg2+ but also provides multiple hydrogen diffusion channels. These findings are of particularly scientific importance for the design and preparation of highly active catalysts for hydrogen storage in light-metal hydrides.

Improved hydrogen storage properties of low-cost Ti–Cr–V alloys by minor alloying of Mn

V-based BCC solid-solution alloys have been considered as promising hydrogen storage materials due to their high hydrogen storage capacity; however, the low effective hydrogen desorption capacity and high cost of pure V have limited their practical application in fuel cell vehicles or devices. Herein, a low-V TiCr1.2(V–Fe0.203)0.6 hydrogen storage alloy with a hydrogen storage capacity of 3.35 wt% has been developed by using a low-cost FeV80 as raw material. To further increase the effective hydrogen desorption capacity, cheap Mn is first used to partially substitute for Cr in FeV80-based alloy. The Mn substitution alloy achieves an effective hydrogen desorption capacity of 2.07 wt% cutting-off at 0.1 MPa with good activation performance. It is ascribed that the minor alloying of Mn increases the dehydrogenation plateau pressure and reduces the hysteresis and the enthalpy change value. The dehydrogenation enthalpy decreases from 34.84 kJ/mol to 31.51 kJ/mol. The synergistic effect of Mn and Fe increases the abundance of the C14 Laves phase, which plays a catalytic role in hydrogen absorption and desorption. The cost of TiCr1.1Mn0.1(V–Fe0.203)0.6 alloy is much lower than that of using pure V, and even lower than some AB2 alloys based on cost estimation. The results of this study would provide a reference for the application of low-cost Ti–Cr-(FeV80) alloys for hydrogen storage.

The mechanistic role of Ti4Fe2O1-x phases in the activation of TiFe alloys for hydrogen storage

TiFe alloy is considered an excellent candidate for stationary hydrogen storage owing to its superior hydrogen storage properties. However, the requisite for activation at high temperatures has hindered the practical application of TiFe alloy for hydrogen storage. This work investigates the activation of TiFe alloys with different Ti/Fe ratios. Results show that the TiFe0.90 alloy can be activated at room temperature and moderate hydrogen pressure (80 bar) compared to the poor activation kinetics of equimolar TiFe alloy. Microstructural characterization and surface analysis indicate that a higher content of Ti4Fe2O1-x phase formed in the TiFe0.9 alloy than in the TiFe0.95 and TiFe alloys. The embedded Ti4Fe2O1-x phase in the TiFe matrix plays a critical role in the overall activation processes, which serves as a conduit for hydrogen to interact with TiFe when it cracks during the initial stage of hydrogenation. The activation behavior is described in the following steps: (1) hydrogen absorption by the Ti4Fe2O1-x oxide on the surfaces of the TiFe matrix; (2) the Ti4Fe2O1-x cracks; (3) cracks extend into the TiFe matrix; (4) TiFe absorbs hydrogen. Understanding the activation behavior is critical to designing TiFe-based alloys with improved hydrogen storage properties.

Improved Hydrogen Storage Properties and Air Stability of Metal Hydrides by Constructing Heterophase Composites

Improved Hydrogen Storage Properties and Air Stability of Metal Hydrides by Constructing Heterophase Composites

Improved Hydrogen Storage Properties of Ti23V40Mn37 Alloy Doped with Zr7Ni10 by Rapid Solidification

Improved Hydrogen Storage Properties of Ti23V40Mn37 Alloy Doped with Zr7Ni10 by Rapid Solidification

The rare earth doped Mg2Ni (0 1 0) surface enhances hydrogen storage

Rare earth doping has been proved to be an effective method to improve hydrogen storage properties of Mg-based alloys. In this work, the effect of rare earth (Y, Ce, La, Sc) doping on the thermal stability, electronic property and hydrogen adsorption/desorption behavior of Mg2Ni (010) surface are systematically investigated by first principles calculation. The results show that rare earth doping in Mg2Ni (010) surface are thermodynamic feasible. The calculated electronic structures shown that rare earth atoms weaken the binding strength between H and Mg2Ni (010) substrate, thus reduce the hydrogen diffusion and desorption energies barriers, and improve the hydrogen storage properties of Mg2Ni. Among the four rare earth elements, Ce shows the best potential. Notably, the substitution doping of Ce to Mg atom significantly reduces the H diffusion barrier by 0.32 eV and H2 desorption barrier by 1.0 eV. This discovery provides a direction for the preparation of rare earth doped Mg2Ni hydrogen storage materials.

Structural features of 18R-type long-period stacking ordered phase in Mg85Zn6Y9 alloy and the Ni doping effect on its hydrogen storage properties

Magnesium-based alloys with 18R-type long-period stacking ordered (LPSO) structures have attracted wide attention for structural and functional applications. To understand hydrogen storage properties of 18R phase, the Mg85Zn6Y9 alloy with 94 wt.% of 18R-type LPSO phase is prepared in this work. The 18R phase has a layered structure where Y-Zn-Mg and Mg layers alternately stack along the c-axis. In the Y-Zn-Mg layers, Y, Zn and partial Mg sites are co-occupied by Y and Mg, Zn and Mg, and Mg and Zn/Y atoms, respectively. Thus the 18R phase is easily decomposed into α-MgH2, γ-MgH2, YH2, YH3, C14-type Laves phase MgZn2 and minor CsCl-type Y(Mg,Zn) during ball milling under hydrogen atmosphere. After further hydrogen absorption-desorption cycling, Y(Mg,Zn) disappears gradually and C14 phase transforms into C15-type Laves phase. By contrast, the Mg85Zn6Y9 alloy has better hydrogen storage kinetics and cycle durability than pure Mg because of the catalytic effect of YH2/YH3 on hydrogen absorption-desorption and inhibition role of Laves phase in Mg crystallite growth. Moreover, the introduction of Ni into Mg85Zn6Y9 sample leads to a further decrease in activation energy of hydrogen desorption from 106.39 to 96.78 kJ mol−1 due to the formation of Mg2Ni. This work not only provides new insights into structural features and hydrogen storage characteristics of 18R phase but offers an effective method for improving hydrogen storage properties.

The mechanism and sorption kinetic analysis of hydrogen storage at room temperature using acid functionalized carbon nanotubes

The present work investigates the effect of acid functionalization of multiwalled carbon nanotubes (MWCNTs) on the physisorption based mechanism of hydrogen storage at room temperature. For this purpose, a suite of functionalized CNT samples is synthesized and subjected to a comprehensive range of material characterization techniques and hydrogen storage measurements. Nitric acid (HNO3) and the mixture of sulphuric acid and nitric acid (H2SO4:HNO3) are used for the synthesis at oxidation temperatures of 80 °C and 100 °C. Electron microscopy and X-ray photoelectron spectroscopy results reveal that acid functionalization causes major alternation in the physicochemical properties of the CNTs due to the varied concentration of oxygen functional groups. Particularly, the H2SO4:HNO3 functionalized sample at 100 °C is found to have the highest interlayer spacing, oxygen to carbon ratio (26.09 at. %), defect content, and specific surface area (215.3 m2/g). These features collectively contribute to substantially improved hydrogen storage properties, including a ∼150% increase in the hydrogen storage capacity at 298 K and 50 bar. Furthermore, kinetic analysis shows that the desorption follows a multiple diffusion process which is sensitive to the oxygen functional groups and structural defects, hence reducing the rate of desorption; whereas the adsorption is controlled by a more rapid, three-dimensional diffusion process.

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.