Remarkable enhancement in durability of ZrCo alloy against hydrogen induced disproportionation by Ti and Nb co-substitution

Considering the thermodynamic stability of various hydrides, a strategy has been employed to improve the hydrogen isotope storage properties of ZrCo alloy which involves partial co-substitution of Zr with Ti and Nb. Herein, alloys of composition Zr_0.8Ti_0.2-xNb_xCo (x = 0.05, 0.1, 0.15) is prepared, characterized and the effect of Ti and Nb doping on hydrogen storage properties of parent ZrCo alloy is investigated. XRD analysis confirmed the formation of desired pure cubic phase of all the synthesized alloys similar to ZrCo phase. The presence of a single plateau in hydrogen desorption pressure-composition isotherms confirms single step hydrogen absorption-desorption behavior in Zr_0.8Ti_0.2-xNb_xCo alloys. The equilibrium pressure of hydrogen desorption decreases marginally with increasing Nb content in Zr_0.8Ti_0.2-xNb_xCo alloys which is further corroborated by differential scanning calorimetry measurements. Investigation of hydrogen induced disproportionation behavior in ITER-simulating condition revealed substantial impact of co-substitution of Ti and Nb on anti-disproportionation properties of ZrCo alloy. These remarkable properties make the Ti and Nb co-substituted quaternary alloys a desirable material for hydrogen isotope storage and delivery application.     

MgH2–Nb2O5 investigated by in situ synchrotron X-ray diffraction

In situ real time synchrotron radiation powder X-ray diffraction (SR-PXD) experiments are utilized to study changes in the crystalline compounds under dynamic hydrogenation and dehydrogenation reactions of MgH₂ ball milled with 8 mol% Nb₂O₅. The ball milling conditions were systematically varied to prepare three samples with different reactivity. Up to eight full cycles of hydrogen release and uptake were investigated for each sample, which reveal that Nb₂O₅ reacts with Mg forming a ternary oxide, Mg_xNb_1−xO. The PXD data for the ternary oxide is similar to that observed for the isostructural compounds MgO and NbO although shifted to lower Bragg diffraction angles revealing an expansion of the unit cell. Rietveld refinements suggest that Mg_xNb_1−xO has a limiting composition of x ∼ 0.6 after eight cycles of hydrogen release and uptake. At elevated temperatures Nb(II) is reduced to metallic Nb(0) and extracted from the ternary oxide and forms in a reaction with Mg. This work suggests that a ternary solid solution Mg_xNb_1−xO is the active material responsible for the prolific kinetic properties for the additive Nb₂O₅. Mg_0.6Nb_0.4O has a ∼4.6% larger unit cell volume as compared to the binary oxides, MgO and NbO, which may lead to formation of cracks and hydrogen diffusion pathways in dense magnesium oxide surface layers.     

Enhancement of hydrogen storage properties of Li12+xMg3-xSi4-ySny (x=y=0.48) phase by modification with LixZnO/La2O3-CNT composites

Two kinds of Li_xZnO-CNT and La₂O₃-CNT composite additives (CA) are employed to improve the hydrogen absorption/desorption processes of Li_12+xMg_3-xSi_4-ySn_y phase. The effect of the addition of composite additives on the improvement of hydrogen sorption kinetics of intermetallic phase is due to the following factors: CA are more stable than Li contain intermetallic; CA provides diffusion pathways to most of the grains inside the material, where the dissociation of H₂ molecules into H atoms takes place; CA surface has a relatively higher reactivity to H₂ dissociation. The substituted (Si atoms by Sn) and doped by La₂O₃-CNT composite Li_12+xMg_3-xSi_4-ySn_y alloy have the highest uptake and release capability (9.8 wt%). Li_xZnO-CNT give 9.3 wt% hydrogen uptake and release, which are still much better than undoped Li_12+xMg_3-xSi_4-ySn_y (8.9 wt%). Li_12+xMg_3-xSi_4-ySn_y is a maximally disordered intermetallic phase (MD-IP) with a cubic structure (I-43d, a = 10.7409(8) Å) related to Cu₁₅Si₄-type.     

Hydrogen storage by Mg-based nanocomposites

Hydrogen storage materials research is entered to a new and exciting period with the advance of the nanocrystalline alloys, which show substantially enhanced absorption/desorption kinetics, even at room temperatures. In this work, hydrogen storage capacities and the electrochemical discharge capacities of the Mg₂(Ni, Cu)-, LaNi₅-, ZrV₂-type nanocrystalline alloys and Mg₂Ni/LaNi₅-, Mg₂Ni/ZrV₂-type nanocomposites have been measured. The electronic properties of the Mg₂Ni_1-xCu_x, LaNi₅ and ZrV₂ alloys were calculated. The nanocomposite structure reduced hydriding temperature and enhanced hydrogen storage capacity of Mg-based materials. The nanocomposites (Mg,Mn)₂Ni (50 wt%)-La(Ni,Mn,Al,Co)₅ (50 wt%) and (Mg,Mn)₂Ni (75 wt%)-(Zr,Ti)(V,Cr,Ni)_2.4 (25 wt%) materials releases 1.65 wt% and 1.38 wt% hydrogen at 25 °C, respectively. The strong modifications of the electronic structure of the nanocrystalline alloys could significantly influence hydrogenation properties of Mg-based nanocomposities.     

Improving hydrogen permeability and sustainability of Nb30Ti35Co35 eutectic alloy membrane by substituting Co using Fe

The microstructure and hydrogen permeation performance of Nb₃₀Ti₃₅Co_35-xFe_x (x = 0, 5, 10, 15, 20) alloys have been investigated. With Fe less than 15 at%, the as-cast Nb₃₀Ti₃₅Co_35-xFe_x ingots exhibit fully eutectic structure. When the Fe content is higher than 15 at%, primary bcc-(Nb, Ti) phase appears in combination with eutectic structure. Substituting Co using Fe leads to slightly increased hydrogen solubility but highly enhanced hydrogen permeability, which comes mainly from the increased hydrogen concentration-independent diffusion coefficient D1. With Fe content up to 10 at%, Nb₃₀Ti₃₅Co_35-xFe_x membranes exhibit stable and higher hydrogen permeation flux than Nb₃₀Ti₃₅Co₃₅ at 673 K during hydrogen permeation test up to 72 h. Nb₃₀Ti₃₅Co_35-xFe_x alloys of fully eutectic structures exhibit no hydrogen-induced failure when cooled down to room temperature under hydrogen atmosphere, indicating the potential application of the membrane at lower temperature range. An optimal combination of hydrogen permeability and hydrogen embrittlement resistance is achieved at 10 at% Fe, since further increase of Fe leads to comparable D1 as that of Nb₃₀Ti₃₅Co₂₅Fe₁₀ but higher hydrogen solubility.     

Relationship between hydrogen permeation and microstructure in Nb–TiNi two-phase alloys

The relationship between the microstructure and hydrogen permeability of the as-cast two-phase Nb–TiNi alloys is investigated and discussed on the basis of the mixing rule. The alloy compositions consisted of the bcc-(Nb, Ti) and B2–TiNi phases are expressed as (Nb₄Ti₄₆Ni₅₀)_1−x(Nb₈₅Ti₁₃Ni₂)_x. The alloy for x = 0.19 has a fully eutectic structure of the (Nb, Ti) and TiNi phases in the as-cast state. The hydrogen permeability of this alloy corresponds to that of a model alloy in which these two phases are distributed randomly. The primary TiNi and (Nb, Ti) phases are formed in the alloys for x < 0.19 and x > 0.19, respectively. Their volume fractions decrease and increase with x, respectively. According to the mixing rule, the hydrogen permeability of alloys having a primary (Nb, Ti) phase can be expressed as the model alloy in which the primary phase is isolated in the eutectic structure. However, the hydrogen permeability of alloys having a primary TiNi phase is higher than that expected for the above model alloy.     

Theoretical and experimental study of the titanium substituted Mg2-xTixNi alloys and Mg2-xTixNiH4 hydrides

The formation of the Ti substituted Mg₂Ni alloys, a promising hydrogen storage material for various applications is studied in detail. Mg_1.95Ti_0.05Ni alloy and ribbons are successfully prepared by vacuum arc melting and melt spinning methods. The phases, microstructures, and thermal behavior of the alloys and ribbons are characterized by XRD, SEM, TEM, DTA/TG. Sievert-type apparatus is used to study hydrogen sorption properties. Apart from the dominant Mg₂Ni phase, the formation of MgNi₂, Mg, and Ni₃Ti phases is seen in both Mg_1·95Ti_0·05Ni alloy and ribbons. During the initial three cycles, Mg_1·95Ti_0·05Ni ribbons showed 2 wt % hydrogen storage capacity. To explain the atomic-scale influence of Ti dopant in the studied alloys and hydrides, FP(L)APW + lo method based on Density Functional Theory (DFT) is applied to Mg_2-xTi_xNi (x = 0.25 and 0.5) alloys and Mg_2-xTi_xNiH₄ (x = 0.25 and 0.5) hydrides. An increase in the Ti dopant on the Mg site leads to the hydrides destabilization. Bader's charge density topology analysis provides insight into the charge transfer and bonding between the constituent atoms.     

The role of magnesium on properties of La3-xMgxNi9 (x=0, 0.5, 1.0, 1.5, 2.0) hydrogen storage alloys from first-principles calculations

The present work gives the electronic structures of La_3-xMg_xNi₉ (x = 0.0–2.0) alloys by first-principles calculations using the generalized gradient approximation of Perdew-Wang 91 (GGA-PW91) method within Cambridge Serial Total Energy Package (CASTEP), aiming at gaining insight into the hydrogen storage mechanism of La_3-xMg_xNi₉ alloys modified by Mg. The results show that the La_3-xMg_xNi₉ alloys consist predominantly of interactions between La-Ni, Ni-Ni or/and Mg-Ni. Among them, La-Ni interaction is the major factor controlling the structural stability of the alloys. Mg substitution increases the La-Ni bonding interactions to achieve stable Mg-containing metal matrices for reversible hydrogen absorption-desorption. This is particularly obvious at high Mg composition, as the La-Ni interactions gradually increase with Mg content. The increase of La-Ni interactions coupled with the decrease of Mg-Ni and Ni-Ni interactions will relieve the hydrogen-induced amorphization and disproportionation, and subsequently enhance the cyclic stability of La_3-xMg_xNi₉ alloys at high Mg content. However, Mg substitution for La leads to a subsequent contraction in cell volume, dramatically reducing the reversible H capacity at high Mg composition such as LaMg₂Ni₉. Suitable Mg content in La-Mg-Ni systems, such as an approximately range x = 1.0–1.4 in La_3-xMg_xNi₉ alloys, is required in trade-off between hydrogen storage capacity and cycle life.     

Effect of niobium on the microstructure,hydrogen embrittlement,and hydrogen permeability of NbxHf(1−x)/2Ni(1−x)/2 ternary alloys

The influence of niobium (Nb) on the microstructure, hydrogen embrittlement, and hydrogen permeability of the Nb_xHf_(1−x)/2Ni_(1−x)/2 ternary alloys has been studied in particular. The results show that the quantity of the primary (Nb, Hf) phase decreases with the increase of Nb content from 14 mol% to 16 mol%, and then increases with the increase of the Nb content from 16 mol% to 40 mol%. The Nb₁₄Hf₄₃Ni₄₃ alloy is brittle at all temperatures from 523 K to 673 K, as it possesses the largest amount of the B_f-HfNi compound; however, the Nb₄₀Hf₃₀Ni₃₀ alloy has high resistance to hydrogen embrittlement at all temperatures from 523 K to 673 K, as it possesses the largest amount of the primary (Nb, Hf) phase. The hydrogen permeability (Φ) increases with the increase in Nb content, as the quantity of the primary (Nb, Hf) phase in the Nb_xHf_(1−x)/2Ni_(1−x)/2 ternary alloys also increases with the increase in Nb content.     

Sensitivity of ferromagnetic resonance in PdCo alloyed films to hydrogen gas

In this work we study the ferromagnetic resonance (FMR) response of Co_xPd_1-x alloy samples with varying compositions (x = 0.65, 0.39, 0.24 and 0.14). We find significant differences in the FMR response of the samples to the presence of hydrogen gas in the samples’ environment. Without any special processing, the films with x = 0.39 and 0.24 demonstrated behaviour which is promising for application in hydrogen gas sensing. Using FMR in the alloy thin films, we were able to measure hydrogen gas concentration in a very broad range - from 0.05% to 100%.     

Microstructure and electrochemical performance of Zn-doped of Mg2Ni1-xZnx hydrogen storage alloys

The microstructures, electrochemical, thermodynamic properties and desorption kinetics of as-cast Mg₂Ni_1-xZn_x (x = 0, 0.08, 0.17, 0.25, 0.33, or 0.41) hydrogen storage alloys are investigated in this study. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results demonstrated that the Mg₂Ni_1-xZn_x alloys are comprised of multiphase structure, thereinto, the diffraction peak of the major phase Mg₂Ni is shifted to a small angle, and its unit cell volume is increased obviously. It was found that the maximum discharge capacity of the alloy electrode firstly increases and then decreases with the increase of the Zn content, and is 52.22 mAh/g when the x = 0.25. The PCT curves showed that the equilibrium hydrogen pressure of alloys is increased with increasing Zn content, which is mainly caused by the reducing of thermodynamic stability for the metal hydride by addition of Zn. Mg₂Ni_0.67Zn_0.33 alloy has the lowest value of hydrogen desorption enthalpy (ΔH) and entropy (ΔS), which are 66.5 kJ/mol and 111.5 J/K/mol, respectively. It is also found that the addition of Zn in the Mg₂Ni alloys significantly reduced their dehydrogenation activation energy (E_a). The Mg₂Ni_0.75Zn_0.25 alloy has the lowest E_a value (17.01 kJ/mol), which is much lower than that (46.07 kJ/mol) of the free Zn Mg₂Ni. This result is confirmed and in good agreement with the hydrogen diffusion rate (5.3068 cm²/s). However, the surface of the Zn-doped alloy is more easily corroded, leading to reduced capacity retention rate.     

Isotope effect on hydrogen storage properties of Ti and Nb co-substituted ZrCo alloy

In our previous study, we showed that the anti-disproportionation properties of Zr_0.8Ti_0.2-xNb_xCo alloys were remarkably improved by the co-substitution of Zr with Ti and Nb. However, the practical application of these alloys in handling of hydrogen isotopes necessitates the first hand knowledge of hydrogen isotope effect. Herein, we discuss the hydrogen isotope effect on storage properties of Zr_0.8Ti_0.2-xNb_xCo alloys. According to PCT measurements on desorption of deuterium from the Zr_0.8Ti_0.2-xNb_xCo deuterides and comparison with corresponding hydrides, the deuterides require relatively lower temperature to achieve the desired equilibrium pressure. DSC measurements reveal a significant decrease in the activation energy for hydrogen/deuterium desorption reactions when Zr is substituted with Ti and Nb. Furthermore, it is observed that the activation energy of deuterium desorption is lower than the desorption of hydrogen from analogous hydride. Isotope effect on isothermal disproportion studies on Zr_0.8Ti_0.2-xNb_xCo-deuterides divulge that Zr_0.8Ti_0.2-xNb_xCo-deuterides have superior anti-disproportionation properties over corresponding hydrides, and further improvement is anticipated for the Zr_0.8Ti_0.2-xNb_xCo-tritides. This study revealed the significant impact of Ti and Nb co-substitution on hydrogen isotope storage properties of Zr_0.8Ti_0.2-xNb_xCo alloys, making them potential candidates for handling hydrogen isotopes.     

Nanocrystalline structure and electrochemical hydrogen storage properties of the as-milled Mg–V–Ni–Fe–Zn-based materials

Among the electrode materials for Ni-MH batteries, the Mg alloy electrodes such as MgNi, Mg₂Ni, REMg₁₂, La₂Mg₁₇ are considered the most suitable anode materials due to their high discharge capacity and low cost. However, the poor electrochemical cycling stability prevents its practical application. In this paper, Mg_50-xV_xNi₄₅Fe₃Zn₂ (x = 0, 1, 2, 3, 4) + 50 wt% Ni alloys were prepared by partially replacing Mg with V and using mechanical ball milling techniques with amorphous and nanocrystalline structures. Electrochemical tests showed that the ball-milled alloy had good electrochemical uptake and release performance. The maximum release performance is achieved in the first cycle. After that, the discharge level and cycle stability increased significantly with increasing ball grinding time and V content.     

Hydrogen storage properties of Nb–Hf–Ni ternary alloys

The hydrogen storage properties of Nb_xHf_(1−x)/2Ni_(1−x)/2 (x = 15.6, 40) alloys were investigated with respect to their hydrogen absorption/desorption, thermodynamic, and dynamic characteristics. The PCT curves show that all the specimens can absorb hydrogen at 303 K, 373 K, 423 K, 473 K, 523 K, 573 K, and 673 K, but they couldn't desorb hydrogen below 373 K. The maximum hydrogen absorption capacity reaches 1.23 wt.% for Nb_15.6Hf_42.2Ni_42.2 and 1.48 wt.% for Nb₄₀Hf₃₀Ni₃₀ at 303 K at a pressure of 3 MPa. When the temperature was increased, the hydrogen absorption capacities significantly decreased. However, the hydrogen equilibrium pressure increased. When the temperature exceeded 523 K, the hydrogen equilibrium pressure disappeared. When niobium content was increased, the kinetic properties of hydrogen absorption/desorption improved. The results from the microstructure analysis show that both alloys consist of the BCC Nb-based solid solution phase, the B_f-HfNi intermetallic phase, and the eutectic phase {B_f-HfNi + BCC Nb-based solid solution}. When the Nb content was increased, the volume fraction and Nb content in the Nb-based solid solution phase increased. Thus, the improved kinetics is related to the increase in the primary BCC Nb-based solid solution in the Nb₄₀Hf₃₀Ni₃₀ alloy. The kinetic mechanisms of hydrogen absorption/desorption in these two alloys are found to obey the chemical reaction mechanism at all temperatures tested.     

Hydrogen storage properties of Mg–Nb@C nanocomposite: Effects of Nb nanocatalyst and carbon nanoconfinement

The Mg–Nb@C nanocomposite has been synthesized by a reactive gas evaporation method to simultaneously achieve carbon nanoconfinement and add Nb nanocatalyst. The size of Mg particles is range from 14 to 26 nm with average size of 20 nm. The small Nb catalyst about 5 nm are decorated in Mg particles, and the proportion of Nb is about 8 wt%. The amorphous carbon layer with thickness of 2 nm is coated on the surface of Mg–Nb nanocomposite. The nanocomposite can absorb 6.4 wt% H₂ and desorb 6.3 wt% H₂ in 5 min at 673 K. At 573 K, it can also uptake 5.8 wt% H₂ in 10 min and release 4.8 wt% H₂ in 60 min. The E_a for hydrogenation and dehydrogenation are reduced to 60.2 and 59.7 kJ mol^?1, respectively. Carbon nanoconfinement and Nb nanocatalyst effectively improve the hydrogen sorption kinetic of Mg.     

Novel B-site substituted KCuTa3-xNbxO9 solid solution photocatalysts with modulated band structure for visible-light-driven hydrogen evolution

Perovskite-like metal oxides (PLMOs), featuring unique structural and optical properties, exhibit great potential in photocatalytic water splitting field. However, the wide bandgap and strong carrier recombination severely suppress their photocatalytic hydrogen production activity. Thus, design and development of novel PLMO photocatalyst with extended photo-response range and enhanced photo-generated charge separation/transport efficiency remains an ongoing challenge. Herein, a series of novel B-site substituted KCuTa_3-xNb_xO₉ solid solution photocatalysts were synthesized via a simple solid-state reaction method. With an increased content of Nb, a distinct red-shifted of the optical absorption edge of KCuTa_3-xNb_xO₉ solid solution was observed, leading to a decreased bandgap (from 2.69 to 1.91 eV), and a positive shift of the conduction band bottom (from −0.54 to −0.49 eV vs RHE). All of the Nb-substituted KCuTa₃O₉ solid solutions exhibit enhanced separation efficiency of photoinduced charge carriers, which leads to increased hydrogen evolution activity, among which KCuTa_0.75Nb_2.25O₉ exhibits the highest hydrogen evolution rate of 2.16 μmol h⁻¹ under the visible light irradiation (λ > 420 nm), which is approximately 7-fold higher than that of the pure KCuTa₃O₉. This study demonstrates the potential of modulating band structure through constructing solid solutions for efficient perovskite-like metal oxides photocatalysis.     

Hydrogen storage properties of Mg-10 wt% Ni alloy co-catalysed with niobium and multi-walled carbon nanotubes

Mg-10 wt% Ni alloys containing up to 1 wt% Nb were fabricated by a casting technique, followed by ball-milling with 5 wt% multi-walled carbon nanotubes. Further mechanical alloying with 1.5, 3, and 5 at % Nb was applied to a cast Mg-10 wt% Ni-370 ppm Nb alloy to investigate the catalytic role of Nb in hydrogen dissociation. The microstructure and distribution of Nb and Mg₂Ni in the alloys were characterised by SEM. The absorption and desorption kinetics of the samples were measured by Sieverts’ apparatus at various temperatures. The results show that addition of Nb during casting accelerates the hydrogen diffusion compared to the cast binary Mg-10 wt% Ni alloy. Moreover, ball-milling of the alloy with metallic niobium leads to the formation of BCC phase of Mg-Nb solid solution, which significantly improves the hydrogenation properties of the alloy. DSC results show that mechanical alloying of Mg-10 wt%Ni-370 ppm Nb with Nb in excess of 1.5 wt% decreases the desorption temperature by approximately 100 °C compared to the ball-milled cast alloy.     

Effects of Zr addition on electrochemical characteristics of MgTiMnNi hydrogen storage alloys

The electrochemical hydrogen storage properties of 25 h milled Mg_0.80Ti_0.175Mn_0.025Zr_xNi_1-x (x = 0, 0.025, 0.05, 0.1) quinary alloys were investigated. The substitution of Zr for Mg or Ni leads to an increase in structural disorder and amorphization. Thus, the maximum discharge capacity and the cycling stability of MgNi-based alloys can be enhanced. The x-ray diffraction patterns indicate that all additive elements are entirely dissolved in the synthesized alloys, and amorphous structure was successfully obtained by 25 h milling. Among the milled alloys, the Mg_0.80Ti_0.175Mn_0.025Zr_0.10Ni_0.90 alloy exhibited the best discharge capacity of 604 mA h g⁻¹ at the initial charge/discharge cycle. The obtained results demonstrate that using multi-component compositions is beneficial for enhancing the structural and cyclic stability of MgNi-based alloys. Therefore, substituting additive elements for Mg or Ni may offer impressive performance for efficient hydrogen storage applications.     

Mechanisms of hydrides’ nucleation and the effect of hydrogen pressure induced driving force on de-/hydrogenation kinetics of Mg-based nanocrystalline alloys

Aiming to gain insight on the hydrogen storage properties of Mg-based alloys, partial hydrogenation and hydrogen pressure related de-/hydrogenation kinetics of Mg–Ni–La alloys have been investigated. The results indicate that the phase boundaries, such as Mg/Mg₂Ni and Mg/Mg₁₇La₂, distributed within the eutectics can act as preferential nucleation sites for β-MgH₂ and apparently promote the hydrogenation process. For bulk alloy, it is observed that the hydrogenation region gradually grows from the fine Mg–Ni–La eutectic to primary Mg region with the extension of reaction time. After high-energy ball milling, the nanocrystalline powders with crystallite size of 12～20 nm exhibit ameliorated hydrogen absorption/desorption performance, which can absorb 2.58 wt% H₂ at 368 K within 50 min and begin to desorb hydrogen from ～508 K. On the other side, variation of hydrogen pressure induced driving force significantly affects the reaction kinetics. As the hydrogenation/dehydrogenation driving forces increase, the hydrogen absorption/desorption kinetics is markedly accelerated. The dehydrogenation mechanisms have also been revealed by fitting different theoretical kinetics models, which demonstrate that the rate-limiting steps change obviously with the variation of driving forces.     

Superior catalysis of NbN nanoparticles with intrinsic multiple valence on reversible hydrogen storage properties of magnesium hydride

Magnesium hydride, as a potential solid state hydrogen carrier has attracted great attention around the world especially in the energy storage domain due to the high hydrogen storage capacity and the good cycling stability. But kinetic and thermodynamic barriers also impede the practical application and development of MgH₂. Nanoscale catalysts are deemed to be the most effective measure to overcome the kinetic barrier and lower the temperature required for hydrogen release in MgH₂. NbN nanoparticles (~20 nm) with intrinsic Nb³⁺-N and Nb⁵⁺-N were prepared using the molten salt method and used as catalysts in the MgH₂ system. It is found that the NbN nanoparticles exhibit a superior catalytic effect on de/rehydrogenation kinetics for the MgH₂/Mg system. About 6.0 wt% hydrogen can be liberated for the MgH₂+5NbN sample within 5 min at 300 °C, and it takes 12 min to desorb the same amount of hydrogen at 275 °C. Meanwhile, the MgH₂+5NbN sample can absorb 6.0 wt% hydrogen within 16 min at 150 °C, and absorb 5.0 wt% hydrogen within 24 min even at 100 °C. Particularly, the catalyzed samples exhibit excellent hydrogen absorption/desorption kinetic stability. After multiple cycles, there is no kinetic attenuation and the hydrogen capacity remains at about 6.0 wt%. It is demonstrated that the NbN nanoparticles with intrinsic multiple valence can be the critical effect in improving the hydrogen storage kinetics of MgH₂. The stability of Nb₄N₃ phase and Nb³⁺-N and Nb⁵⁺-N valence states can ensure a stable catalytic effect in the system.