Onset Dehydrogenation Temperature Research Articles

Perovskiet-like BaZrO3 nanocatalyst with rich oxygen vacancies on boosting hydrogen storage property of MgH2

Magnesium hydride (MgH2) as a promising solid hydrogen syorage material has been extensively researched. but the higher separating temperature and sluggish kinetics hinder its large-scale practical application. To solve this problem, a BaZrO3 nanocatalyst with abundant oxygen vancies is manuscripted, exerts significant improvement to the hydrogen storage performance of MgH2. Impressively, the onset dehydrogenation temperature of MgH2-10 wt% BaZrO3-Ov composite is reduced markedly from 390 °C(for pure MgH2) to 260 °C. Additionally, the composite can discharge 4.22 wt% H2 with 10 min at 275 °C and a total dehydrogenation amouut of 5.88 wt% is achieved at 300 °C. For hydrogen absorption, the composite can rapidly recharge hydrogen at a low temperature of 150 °C and approximately 5.08 wt% H2 can be absorbed at 275 °C within 10 min. The dehydrogenation activation energy of BaZrO3-Ov-added MgH2 is as low as 92.61 kJ mol−1 compared to pure MgH2 (164.78 kJ mol−1). Meantime, the composite presents unexceptionable reversible kinetic performance with a retention rate of 97.35 % after 10 cycles. The excellent catalytic effects can be attributed to the in-situ generation of ZrO2-Ov, BaO-Ov and ZrH2 from BaZrO3-Ov during the first de-/rehydrogenation cycle, which function as nanosized active sites on MgH2 matrix to accelerate electron transfer and provide abundant hydrogen diffusion channels. Density functional theory calculations results verify that the Mg–H length and dehydrogenation energy barrier are ameliorated through BaZrO3-Ov. This work provides a unique perspective on modification MgH2 by perovskiet-like BaZrO3-Ov nanocatalyst.

Preparation, characterization and modification of magnesium hydride for enhanced solid-state hydrogen storage properties

Magnesium–magnesium hydride (Mg–MgH2) system has attracted attention worldwide recently because of its simple hydrogenation-dehydrogenation process, the cost-effectiveness of the raw materials, and relatively high hydrogen storage capacity compared to the other metal-metal hydride systems. The present study deals with the optimization of the process parameters for the synthesis of magnesium hydride (MgH2) in sizable quantities using commercial-grade magnesium powder, characterization with respect to hydrogen storage capacity, by thermal dehydrogenation and pH-controlled aqueous hydrolysis. The thermal hydrogenation-dehydrogenation and mild acidified aqueous dehydrogenation behaviour of MgH2 were studied systematically to compare the decomposition kinetics and storage capacity. The superior catalytic effect of V2O5 on decreasing the onset-dehydrogenation temperature of MgH2 is demonstrated. The MgH2-5 wt. % mesoporous V2O5 sample starts releasing hydrogen at 220 °C, which is substantially less than the as-synthesized un-catalysed MgH2 under identical conditions which starts releasing hydrogen at 430 °C. The dehydrogenated MgH2-5wt. %V2O5 could be completely re-hydrogenated at 150 °C. Hydrolysis of as-synthesized MgH2 was demonstrated using an aqueous solution using tartaric acid and the dehydrogenation behaviour was co-related with the pH of the solution. More than 90% hydrogen yield was achieved by the hydrolysis of MgH2 in a tartaric acid solution of pH-4. Based on the result, a hydrogen gas dispenser using solid-state magnesium hydride as a hydrogen source is proposed for laboratory applications for the supply of ultra-pure hydrogen for various reactions and crystal growth experiments.

Binding energy crossover mechanism enables low-temperature hydrogen storage performance of dual-phase TiZrCrMnNi(VFe) high-entropy alloy

High-entropy hydrogen storage alloys possess immense potential for composition-performance modulation, yet they currently struggle to strike a balance between high capacity, stability, and low-temperature dehydrogenation. In this work, a novel TiZrCrMnNi(VFe) high-entropy alloy (HEA) was designed and dual-phase synergistic effect during the de-/hydrogenation processes was proposed. Specifically, the as-synthesized TiZrCrMnNi(VFe) alloy comprises two approximate C14 Laves phases, denoted as C14-Ⅰ and C14-Ⅱ phases. A noteworthy feature is that TiZrCrMnNi(VFe) HEA can rapidly reach a saturated capacity of 1.83 wt% H2 at 0 °C without any activation treatment, and then desorb 1.77 wt% H2 with a low onset dehydrogenation temperature of 20 °C. Based on experimental evidence and DFT calculations, it is concluded that dual-phase structure offers a distinguished phenomenon of binding energy crossover. Accordingly, compared with a single C14 phase, the structure with two C14 phases produces dual-phase synergistic effect, facilitating the de-/hydrogenation processes by lowering the energy barrier. In addition, the existence of phase boundaries also improves the activation performance of the alloy. Consequently, TiZrCrMnNi(VFe) HEA has excellent activation and low-temperature de-/hydrogenation performance. The innovative outcomes here provide a valuable reference for subsequent research on the low temperature de-/hydrogenation of HEAs.

Inducing One-Step Dehydrogenation of Magnesium Borohydride via Confinement in Robust Dodecahedral Nitrogen-Doped Porous Carbon Scaffold.

A dodecahedral activated N-doped porous carbon scaffold is synthesized and used for the nanoconfinement of Mg(BH4)2. The optimized mesoporous scaffold possesses an accumulated pore width of 2.65nm, high specific surface area (3955.9 m2g-1), and large pore volume (2.15 cm3g-1), providing ample space for the confinement of Mg(BH4)2 particles and numerous surface active sites for interactions with the same. The confined Mg(BH4)2 system features a dehydrogenation onset temperature of 81.5°C, an extremely high capacity of 10.2 wt% H2, and an almost single-step dehydrogenation profile. Moreover, the system exhibits superior capacity retention of 82.7% after 20 cycles at a moderate temperature of 250°C. Precise activation control enables a transformation from microporous carbon materials to mesoporous ones, and hence the efficient nanoconfinement of Mg(BH4)2 and realization of one-step dehydrogenation. The evolution of borohydride intermediates is systematically revealed throughout the cycling process. Density functional theory calculations demonstrate defective N heteroatoms within the scaffold are vital in reducing the strength of B─H bonds, and the N-doped carbon can facilitate decomposition of the irreversible MgB12H12 intermediate. This study opens up new avenues for designing robust carbon scaffolds doped with heteroatoms and analyzing intermediate evolution in nanoconfined Mg-based borohydride systems.

Constructing Ni/CeO2 synergistic catalysts into LiAlH4 and AlH3 composite for enhanced hydrogen released properties

The high hydrogen release temperature and thermodynamic stability of the coordination hydride LiAlH4 render it unsuitable for direct application. This work intends to improve the hydrogen release properties via compositing LiAlH4 and AlH3 with similar initial hydrogen release temperatures and introduce efficient additive Ni/CeO2 composite. The thermal stability of the composite system LiAlH4-AlH3 is enormously reduced compared to that of LiAlH4. In addition, the preferential release of hydrogen from LiAlH4 in the composite system provides additional heat for the subsequent release of hydrogen from AlH3, accelerating the hydrogen release process. As a result, LiAlH4-AlH3-Ni/CeO2 composite performs enhanced hydrogen release performance with a hydrogen release capacity of 8.27 wt% hydrogen within 300 ℃ and a dehydrogenation onset temperature as low as 72.9 ℃. The enthalpy change of the first step hydrogen release reaction decreases from −11.99 kJ mol−1 (LiAlH4) to −2.02 kJ mol−1 (LiAlH4-AlH3). Theoretical calculations indicate that both atomic dehybridisation and electron redistribution expedite the breaking of the Al-H bond and the consequent release of hydrogen.

Mxene-supported NbVH nanoparticles as efficient catalysts for reversible hydrogen storage in magnesium borohydride

Bimetallic niobium vanadium hydride nanoparticles (NbVH NPs) anchored on Ti3C2 were synthesized using a facile ball milling method as an effective catalyst for the dehydrogenation kinetics and reversibility of Mg(BH4)2. It was found that the onset dehydrogenation temperature of the Mg(BH4)2 + 30NbVH NPs@Ti3C2 composite was 105.7 °C and released 9.07 wt% of hydrogen at 330 °C, while undoped Mg(BH4)2 only released 4.2 wt% of H2 from 248 °C to 330 °C. Additionally, the Mg(BH4)2 + 30NbVH NPs@Ti3C2 composite achieved remarkable hydrogen release of over 9.44 wt% at a temperature as low as 230 °C, indicating unexpected dehydrogenation kinetics. In the reversible hydrogen desorption tests, Mg(BH4)2 + 30NbVH NPs@Ti3C2 released 5.98 wt% of H2 in the 2nd cycle at 250 °C and maintained a reversible capacity of 4.35 wt% after 10 cycles, demonstrating a remarkable enhancement in reversibility. The enhancement in the dehydrogenation kinetics of Mg(BH4)2 could be attributed to the greatly reduced activation energies from 343 kJ·mol−1 and 138.3 kJ·mol−1 to 103.7 kJ·mol−1 and 124 kJ·mol−1. Investigations on the evaluation of catalyst and Mg(BH4)2 during reversible hydrogen storage have revealed that NbVH NPs actually acted as a “bidirectional hydrogen pump”, facilitating both the hydrogen release and uptake from Mg(BH4)2. This strategy of multi-component hydrides may show a new way to design effective catalysts for solid-state hydrogen storage materials.

Heteroatom sulfur exploration for enhancing MgH2 dehydrogenation: A theoretical and experimental analysis

High operating temperatures and sluggish kinetics constrain the commercial application of magnesium-based hydrogen storage materials. To overcome these drawbacks, this work investigates heteroatom sulfur as a catalyst to improve the dehydrogenation of MgH2 using density functional theory (DFT) and experimental validation. Heteroatom sulfur can influence the dehydrogenation of MgH2 by modulating interfacial carbon-magnesium interactions and substituting surface hydrogen sites. In particular, DFT calculations reveal that sulfur functional groups facilitate charge transfer and significantly reduce the energy barrier of MgH2 by 0.32 eV–1.59 eV. Substitution of sulfur atoms at surface hydrogen sites of MgH2 notably improves dehydrogenation by weakening the Mg–H bond and enabling a sulfur-assisted two-step dehydrogenation mechanism. Experimental results further confirm these theoretical findings. The MgH2/900C–20SO2 sample exhibits that the peak dehydrogenation temperature and the onset dehydrogenation temperature were 19.8 °C and 64 °C lower than that of pure MgH2, and a significant reduction in activation energy from 134.52 kJ mol−1 to 92.12 kJ mol−1. This research provides a comprehensive understanding of the catalytic effects of heteroatom sulfur on MgH2 and offers crucial theoretical and practical insights for the development of more efficient magnesium-based hydrogen storage systems.

Nitrogen-Doped Graphene-Supported Nickel Nanoparticles Reveal Low Dehydrogenation Temperature and Long Cyclic Life of Magnesium Hydrides.

Magnesium hydride (MgH2) is a promising hydrogen storage candidate due to its large capacity; however, high dehydrogenation temperature and slow kinetic rates are the main bottlenecks. Herein, we proposed a strategy for designing nitrogen-doped graphene-supported Ni nanoparticles (NPs) (Ni@NC) to tackle these problems. The results showed that the MgH2 + 15 wt % Ni@NC nanocomposite reduced the on-set dehydrogenation temperature to 195 °C, which was 175 °C lower than pristine MgH2. In addition, MgH2 + 15 wt % Ni@NC achieved 1.7 and 6.5 wt % desorption capacities at 225 and 300 °C, respectively, while absorbing 5.5 wt % hydrogen at 100 °C. The MgH2 + 15 wt % Ni@NC nanocomposite showed high cyclic stability, achieving 98.0% capacity retention after 100 cycles at 270 °C with negligible loss in capacity. This remarkable hydrogen storage performance can be attributed to the homogeneous distribution of Ni NPs on N-doped graphene layers, in situ formed Mg2NiH2 NPs, and multiphasic regions, promoting the nucleation and growth process during hydrogenation/dehydrogenation, which stabilized and improved the cyclic stability. This strategy paves the way to developing high-performance MgH2 for large-scale applications.

Single-Atom Ni Supported on TiO2 for Catalyzing Hydrogen Storage in MgH2.

As an efficient and clean energy carrier, hydrogen is expected to play a key role in future energy systems. However, hydrogen-storage technology must be safe with a high hydrogen-storage density, which is difficult to achieve. MgH2 is a promising solid-state hydrogen-storage material owing to its large hydrogen-storage capacity (7.6 wt %) and excellent reversibility, but its large-scale utilization is restricted by slow hydrogen-desorption kinetics. Although catalysts can improve the hydrogen-storage kinetics of MgH2, they reduce the hydrogen-storage capacity. Single-atom catalysts maximize the atom utilization ratio and the number of interfacial sites to boost the catalytic activity, while easy aggregation at high temperatures limits further application. Herein, we designed a single-atom Ni-loaded TiO2 catalyst with superior thermal stability and catalytic activity. The optimized 15wt%-Ni0.034@TiO2 catalyst reduced the onset dehydrogenation temperature of MgH2 to 200 °C. At 300 °C, the H2 released and absorbed 4.6 wt % within 5 min and 6.53 wt % within 10 s, respectively. The apparent activation energies of MgH2 dehydrogenation and hydrogenation were reduced to 64.35 and 35.17 kJ/mol of H2, respectively. Even after 100 cycles of hydrogenation and dehydrogenation, there was still a capacity retention rate of 97.26%. The superior catalytic effect is attributed to the highly synergistic catalytic activity of single-atom Ni, numerous oxygen vacancies, and multivalent Tix+ in the TiO2 support, in which the single-atom Ni plays the dominant role, accelerating electron transfer between Mg2+ and H- and weakening the Mg-H bonds. This work paves the way for superior hydrogen-storage materials for practical unitization and also extends the application of single-atom catalysis in high-temperature solid-state reactions.

Introducing Ni-N-C ternary nanocomposite as an active material to enhance the hydrogen storage properties of MgH2

The use of Mg-based materials as solid-state hydrogen storage materials can provide a viable solution to the bottleneck hindering the development of hydrogen energy. However, it is necessary to address their excessively stable thermodynamic properties and sluggish kinetic performances. In this study, we prepared a Ni-N-C ternary nanocomposite (designated as Ni@NC) catalyst using Ni-based metal-organic frameworks (Ni-MOFs) as a precursor for catalytic MgH2 hydrogen storage properties. The Ni@NC catalyst exhibited excellent promotion effects on the hydrogen absorption and desorption kinetics and the cycling stability of the Mg-based materials. Notably, the composite exhibited room-temperature hydrogen absorption initiation and an onset dehydrogenation temperature of 188 °C, with complete hydrogenation achieved after holding at 100 °C for 60 min. After undergoing 100 cycles of absorption/dehydrogenation, the capacity retention rate was 99.5 %. The differential scanning calorimetry (DSC) test results indicated that the re-hydrogenated MgH2-Ni@NC composites consist of Mg2NiH4 and MgH2, with corresponding dehydrogenation activation energies of 75.2 and 82.9 kJ mol−1 respectively. The mechanism analysis revealed that Ni@NC was uniformly distributed on the MgH2 surface. During dehydrogenation/rehydrogenation, Mg2NiH4/Mg2Ni “hydrogen pumping” by Ni and MgH2/Mg occurred in situ, the presence of N-C effectively inhibited the expansion of MgH2/Mg, and the enhanced charge transfer effect was facilitated by N in the Ni@NC composite, synergistically enhancing the kinetic performance and cycling stability of MgH2.

Investigation on Nonisothermal Dehydrogenation Behavior of Mg–Ni–La–H Materials Prepared by Mechanochemical Reaction

Mg10NixLa–H alloys are synthesized by mechanochemical reaction starting with Mg–Ni–La multiphase polycrystalline alloys prepared by resistance melting furnace. The nonisothermal hydrogen desorption behaviors are investigated herein. All prepared samples are characterized by scanning electron microscopy, X‐ray diffraction, fully automatic fast surface and porosity analysis meter Brunauer–Emmett–Teller (BET), differential scanning calorimetry, and thermogravimetric analyzer to get information of phase compositions, microstructure, BET surface area, and dehydrogenation properties. The results demonstrate that Mg10NixLa–H exhibits enhanced nonisothermal hydrogen desorption behavior owing to the synergistic effects among hydrides. The main peak dehydrogenation temperatures for Mg10Ni5La–H, Mg10Ni10La–H, and Mg10Ni15La–H alloys are 375.3, 374.4, and 359.7 °C at 5 °C min−1, respectively. And the apparent activation energy for Mg10Ni5La–H, Mg10Ni10La–H, and Mg10Ni15La–H is 111.7, 275.5, and 184.7 kJ mol−1, respectively. However, the actual hydrogen release capacities of Mg10Ni5La–H, Mg10Ni10La–H, and Mg10Ni15La–H are about 5.09, 3.98, and 4.49 wt%, respectively. Mg10Ni15La–H exhibits the lowest onset dehydrogenation temperature due to its reduced particle size and uniformly distributed hydride phase. The modification of Mg‐based hydrogen storage materials by combining mechanochemical reaction and multiple microalloying is essential for further improvement of thermal properties.

Superior catalytic effect of Bi@C on dehydrogenation performance of α-AlH3

The high dehydrogenation temperature of α-AlH3 has always been an important factor hindering its development. In order to solve this problem, we synthesize Bi-MOF by hydrothermal method and burn it under inert gas to obtain Bi@C, which is used as catalyst (xBi@C, x = 3, 5 and 7 wt%) to improve the hydrogen desorption performance of α-AlH3. The dehydrogenation onset temperature of α-AlH3+5 wt% Bi@C drop to 80.4 °C, which is reduced by 43.4% compared with pure α-AlH3. At 120 °C, it can provide a stable hydrogen capacity of 7.45 wt%. In contrast, pure α-AlH3 releases only 6.66 wt% hydrogen at the same time. The density functional theory calculations further indicate that the existence of Bi@C catalyst can make the Al–H bond length increase, more conducive to the release of hydrogen. The results show that the synergistic effect of Bi and porous carbon in Bi@C materials can improve the hydrogen desorption kinetics of α-AlH3, providing a good prospect for the application of α-AlH3 in hydrogen storage.

In Situ Formed Ti/Nb Nanocatalysts within a Bimetal 3D MXene Nanostructure Realizing Long Cyclic Lifetime and Faster Kinetic Rates of MgH2.

Magnesium hydride (MGH) is a high-capacity and low-cost hydrogen storage material; however, slow kinetic rates, high dehydrogenation temperature, and short cycle life hindered its large-scale applications. We proposed a strategy of designing novel delaminated 3D bimetal MXene (d-TiNbCTx) nanostructure to solve these problems. The on-set dehydrogenation temperature of MGH@d-TiNbCTx composition was reduced to 150 °C, achieving 7.2 wt % of hydrogen releasing capacity within the range of 150-250 °C. This composition absorbed 7.2 wt % hydrogen within 5 min at 200 °C and 5.5 wt % at 30 °C within 2 h, while the desorption capacity (6.0 wt %) was measured at 275 °C within 7 min. After 150 cycles at 250 °C, the 6.5 wt % capacity was retained with negligible loss of hydrogen content. These results were attributed to the catalytic effect of in situ-formed TiH2/NbH2 nanocatalysts, which lead to dissociate the Mg-H bonds and promote of kinetic rates. This unique structure paves great opportunities for designing of highly efficient MGHs/MXene nanocomposites to improve the hydrogen storage performance of MGHs.

Application of nitrogen-doped graphene-supported titanium monoxide as a highly active catalytic precursor to improve the hydrogen storage properties of MgH2

MgH2 has broad prospects in energy storage applications; however, its poor thermodynamic properties and slow hydrogen absorption and desorption rates are unsuitable for commercial needs. In the present work, TiO@N-C (denoted as TTONC), a highly active catalytic precursor, was employed to improve the hydrogen storage properties of MgH2. The TTONC-catalyzed MgH2 could uptake hydrogen at room temperature, and the onset dehydrogenation temperature of TTONC-catalyzed MgH2 was 94 °C lower than that of pristine MgH2 (∼300 °C). Dehydrogenated TTONC-catalyzed MgH2 had a capacity retention rate of 95.2% after 50 hydrogen absorption-desorption cycles. The dehydrogenation and hydrogenation apparent activation energies of MgH2-TTONC were 90.5 kJ.mol−1 and 52.7 kJ.mol−1, respectively. The catalytic mechanism analysis revealed that the in situ formed Ti generated TiH2 in the hydrogenation process, and Ti/TiH2 acted as a hydrogen pump to diffuse hydrogen atoms in the hydrogen absorption/desorption process. The formation of stable CN layers with carbon structural defects on the surface of MgH2 inhibited the fragmentation and agglomeration of MgH2 particles, and they served as nucleation sites to enhance hydrogen diffusion. Hence, the dehydrogenation/hydrogenation properties and cyclic stability of MgH2 were greatly enhanced by the addition of TTONC.

Carbon composite support improving catalytic effect of NbC nanoparticles on the low-temperature hydrogen storage performance of MgH2

Ultrafine carbon-based transition metal compounds have been widely investigated as efficient catalysts for enhancing the hydrogen storage performance of magnesium hydride. In this work, the carbon thermal shock method is applied to synthesize the ultrafine carbon-encapsulated NbC nanoparticles with an average grain size of 17.3 nm. The MgH2–10 wt% NbC/C composites show excellent low-temperature hydrogen storage performance with the onset dehydrogenation temperature of 196.1 °C, which is 92.2 °C and 98 °C lower than that of MgH2–10 wt% NbC and undoped MgH2, respectively. Specifically, MgH2–10 wt% NbC/C can absorb 6.71 wt% H2 at 100 °C within 30 min around and retain almost 100% reversible hydrogen desorption capacity after 10 cycles. For the catalytic mechanism, the electron transfer process between multi-valence Nb cations of in-situ formed NbHx and Mg, H atoms can greatly improve the cyclic de/rehydrogenation kinetics of MgH2-NbC/C. Besides, the enhancement of dehydrogenation kinetics can also be ascribed to MgH2 particle refinement by NbC nanoparticles, and destabilization of the Mg-H bond caused by carbon substrate. This investigation not only proves that carbon-encapsulated NbC nanoparticles can greatly enhance the hydrogen storage performance of MgH2 but provides an idea of preparing carbon-based transition metal carbides as effective catalysts for magnesium-based hydrogen storage materials.

In situ formation of TiB2 and TiH2 catalyzed Li/Mg based dual-cation borohydride with a low onset dehydrogenation temperature below 100 °C

Chemical complex borohydride is a promising hydrogen storage material due to its large gravimetric and volumetric hydrogen capacities. However, the high dehydrogenation temperature and sluggish kinetics still place strong restrictions on its practical application in the hydrogen storage field. In this work, a synergetic approach of partial cation substitution and catalysis is developed to enhance the hydrogen storage properties of LiBH4. The Li/Mg based dual-cation borohydride (LiMg2(BH4)5, LMBH) was successfully synthesized by wet chemical ball milling of LiBH4 and MgCl2. The optimal (LMBH (4.5:1) sample, LiBH4 and MgCl2 in molar ratios of 4.5:1, possesses a maximum hydrogen desorption capacity (11.27 wt%) and the outstanding initial decomposition temperature (∼250 °C). Importantly, the LMBH (4.5:1) doped with TiF3 shows a remarkable onset dehydrogenation temperature as low as 97.2 °C, which is about 190 °C lower than that of pristine LiBH4. The LMBH (4.5:1) doped with TiF3 system releases 7.98 wt% H2 within 170 min below 350 °C. And the dehydrogenation product of doped composite can reversibly absorb ∼4.72 wt% H2 at a relatively moderate temperature of 280 °C, which is substantially lower than the reversible hydrogen absorption temperature of previous modified borohydride systems. Based on the structural characteristic analyses, the TiF3 reacts with LMBH (4.5:1) to in-situ form actual catalytic components of TiB2 and TiH2 as the actual catalysts for LMBH (4.5:1), resulting in the improved hydrogen re/dehydrogenation properties. The synergetic modification of Li/Mg dual-cation substitution and TiB2/TiH2 catalysis may lead to the development of light-metal borohydrides with outstanding hydrogen storage properties.

Dual tuning of the de-/hydrogenation thermodynamics and kinetics of the Mg–Ni alloy by introducing the Ag–H bond: enhanced hydrogen storage properties at moderate temperatures

The onset dehydrogenation temperature of Mg85Ni14.8Ag0.2 reduces to 178 °C due to the enhanced hydrogen pumping effect of Mg2NiH4 by adjusting the Ni–H bond.

Superior hydrogen performance of in situ formed carbon modified MgH2 composites.

The MgH2-carbonic combustion product of the anthracene (CCPA) composite was synthesized by hydrogen combustion and mechanically ball-milled method to simultaneously achieve confinement by the in situ formed amorphous carbon. The amorphous carbon derived from the carbonic combustion product of anthracene in the MgH2-CCPA composite led to a significant increase in hydrogen sorption characteristics. The onset dehydrogenation temperature for the MgH2-CCPA composite was reduced to 589 K, which was 54 K less than that of pure milled MgH2. Regarding dehydrogenation kinetics, the MgH2-CCPA composite could release 5.933 wt% H2 within 3000 s at 623 K, while only 3.970 wt% H2 was liberated from the as-milled MgH2 within 3000 s at the same temperature. The MgH2-CCPA composite also exhibited excellent hydrogenation characteristics, absorbing 3.246 wt% of hydrogen within 3000 s at 423 K, which was three times higher than 0.818 wt% uptaken by the pure MgH2. The apparent activation energy (E a) for the dehydrogenation of the MgH2-CCPA composite was significantly reduced from 161.1 kJ mol-1 to 77.5 kJ mol-1. The notable improvement in sorption kinetics of the MgH2-CCPA nanocomposite is ascribed to the in situ formed amorphous carbon during the hydrogenation/dehydrogenation process.

Boosting the hydrogen storage performance of MgH2 by Vanadium based complex oxides

MgH2, a solid-state hydrogen storage material with high storage capacity, is facing the obstacles of high thermodynamic stability and slow reaction kinetics. Herein, different Vanadium (V) based catalysts (V2O5, Fe–V and V–Ni oxides) were synthesized by a hydrothermal method and ball milled with MgH2 to modify its hydrogen storage property. It is observed that the dehydrogenation performance (initial dehydrogenation temperature and desorption rate) of Fe–V oxide doped MgH2 was the best, followed by V2O5 and V–Ni oxide modified systems. The MgH2+7 wt% Fe–V composite exhibited an onset dehydrogenation temperature of 200 °C, 128 °C lower compared with the original MgH2. The absorption performance of MgH2 was also greatly enhanced by Fe–V oxide. The 7 wt% Fe–V modified MgH2 after dehydrogenation began to charge hydrogen from 25 °C to 5.1 wt% hydrogen was absorbed at 150 °C. The activation energy for hydrogen uptake of MgH2 was reduced from 76.5 ± 3.4 kJ/mol to 41.2 ± 4.7 kJ/mol. Additionally, the MgH2+7 wt% Fe–V composite maintained 97.2% hydrogen capacity after10 cycles. Our work here proves that elements substitution is a feasible way to tune the catalytic effect of oxides and may shed light on designing catalysts with higher activation in the future.

High-loading, ultrafine Ni nanoparticles dispersed on porous hollow carbon nanospheres for fast (de)hydrogenation kinetics of MgH2

Magnesium hydride (MgH2) is one of the most promising hydrogen storage materials for practical application due to its favorable reversibility, low cost and environmental benign; however, it suffers from high dehydrogenation temperature and slow sorption kinetics. Exploring proper catalysts with high and sustainable activity is extremely desired for substantially improving the hydrogen storage properties of MgH2. In this work, a composite catalyst with high-loading of ultrafine Ni nanoparticles (NPs) uniformly dispersed on porous hollow carbon nanospheres is developed, which shows superior catalytic activity towards the de-/hydrogenation of MgH2. With an addition of 5 wt% of the composite, which contains 90 wt% Ni NPs, the onset and peak dehydrogenation temperatures of MgH2 are lowered to 190 and 242 °C, respectively. 6.2 wt% H2 is rapidly released within 30 min at 250 °C. The amount of H2 that the dehydrogenation product can absorb at a low temperature of 150 °C in only 250 s is very close to the initial dehydrogenation value. A dehydrogenation capacity of 6.4 wt% remains after 50 cycles at a moderate cyclic regime, corresponding to a capacity retention of 94.1%. The Ni NPs are highly active, reacting with MgH2 and forming nanosized Mg2Ni/Mg2NiH4. They act as catalysts during hydrogen sorption cycling, and maintain a high dispersibility with the help of the dispersive role of the carbon substrate, leading to sustainably catalytic activity. The present work provides new insight into designing stable and highly active catalysts for promoting the (de)hydrogenation kinetics of MgH2.