Combinations of V2C and Ti3C2 MXenes for Boosting the Hydrogen Storage Performances of MgH2

Self-reduced MXene-Metal interaction electrochemiluminescence support with synergistic electrocatalytic and photothermal effects for the bimodal detection of ovarian cancer biomarkers

Novel two-dimensional MXene with unique optical and electrical properties has become a new focus in the field of sensing. In particular, their metallic conductivity, good biocompatibility and high anchoring ability to biomaterials make them attractive candidates. Despite such remarkable properties, there are certain limitations, such as low oxidative stability. MXene-Metal interactions are an effective strategy to maintain the long-term stability of MXene, while also improving the electrochemical activity and optical properties. Herein, a series of MXene/Ag nanocomposites including Ti3C2/Ag, Nb2C/Ag and V2C/Ag were designed based on the surface chemistry characteristics of MXene, where MXene served as the substrate for in-situ growth of silver nanoparticles via self-reduction of Ag(NH3)2+. The results showed that V2C MXene has the strongest self-reducing ability due to its multiple variable valence states, larger interlayer space and more reactive groups. Moreover, V2C/Ag exhibited unexpected oxygen reduction reaction catalytic activity and photothermal performance. In view of which, an electrochemiluminescence-photothermal (ECL-photothermal) immunosensor was developed using V2C/Ag as ECL anchor and photothermal reagent for ultrasensitive detection of Lipolysis stimulated lipoprotein receptor. This work not only provides a simple and effective synthesis method of MXene supported metal nanocomposites, but also provides more inspirations for exploring the efficient biosensing strategies.

Recent progress of MXene as an energy storage material

Thanks to its adjustable interlayer distance, large specific surface area, abundant active sites, and diverse surface functional groups, MXene has always been regarded as an excellent candidate for energy storage materials, including supercapacitors and ion batteries. Recent studies have also shown that MXene can serve as an efficient hydrogen storage catalyst. This review aims to summarize the latest research achievements in the field of MXene, especially its performance and application in energy storage. Different synthesis techniques have different effects on the energy storage performance of MXene. In this review, various common synthesis methods and the latest innovations in synthesis methods are discussed. MXene is prone to oxidation, and how to resist oxidation is also an important topic in MXene research. This article introduces the research results on improving the chemical stability of MXene through annealing. In addition, it aims to gain a deeper understanding of the future development and potential of MXene.

Unveiling the Latest Advancements in Vanadium Carbide MXene based Supercapacitors and their Future Trends

Vanadium-carbide-based MXenes have bewitched the scientific community due to their distinctive characteristics, which make them potential candidates for several technological applications, such as supercapacitors (SCs), batteries, gas separation, biological sensors, and desalination. This article provides an overview of recent developments in the synthesis and applications of vanadium-carbide MXene in SCs. Vanadium carbide is one of the most difficult MXenes to synthesize, and various synthesis techniques, including electrochemical exfoliation and chemical etching, have been utilized to fabricate this material. Additionally, the review article also emphasizes the potential use of vanadium carbide MXene as SCs. Finally, the paper concludes with the challenges faced in the synthesis process and the prospects of vanadium carbide MXene-based material fabrication. Overall, this review article provides in-depth and detailed information on recent research on vanadium carbide MXene and its possible uses.

Solid-solution MAX phase TiVAlC assisted with impurity for enhancing hydrogen storage performance of magnesium hydride

Although MXene catalysts etched from precursor MAX have greatly improved the hydrogen storage performance of magnesium hydride (MgH2), the use of dangerous and polluting etchers (such as hydrofluoric acid) and the direct removal of potentially catalytically active A-layer substances (such as Al) present certain limitations. Here, solid-solution MAX phase TiVAlC catalyst without etching treatment has been directly introduced into MgH2 system to improve the hydrogen storage performance. The optimal MgH2-10 wt% TiVAlC can release about 6.00 wt% hydrogen at 300 °C within 378 s and absorb about 4.82 wt% hydrogen at 175 °C within 900 s. After 50 isothermal hydrogen ab/desorption cycles, the excellent cyclic stability and capacity retention (6.4 wt%, 99.6%) can be found for MgH2-10 wt% TiVAlC. The superb catalytic activity of TiVAlC catalyst can be explained by abundant electron transfer at external interfaces with MgH2/Mg, which can be further enhanced by impurity phase Ti3AlC2 due to strong H affinity brought from abundant electron transfer at internal interfaces (Ti3AlC2/TiVAlC). The influence of impurity phase which is common in MAX phase on the overall activity of catalysts has been firstly studied here, providing a unique method for designing composite catalyst to improve hydrogen storage performance of MgH2.

PdNi Biatomic Clusters from Metallene Unlock Record-Low Onset Dehydrogenation Temperature for Bulk-MgH2

Hydrogen storage has long been a priority on the renewable energy research agenda. Due to its high volumetric and gravimetric hydrogen density, MgH2 is a desirable candidate for solid-state hydrogen storage. However, its practical use is constrained by high thermal stability and sluggish kinetics. Here, PdNi bilayer metallenes are reported as catalysts for hydrogen storage of bulk-MgH2 near ambient temperature. Unprecedented 422 K beginning dehydrogenation temperature and up to 6.36 wt.% reliable hydrogen storage capacity are achieved. Fast hydrogen desorption is also provided by the system (5.49 wt.% in 1 h, 523 K). The in situ generated PdNi alloy clusters with suitable d-band centers are identified as the main active sites during the de/re-hydrogenation process by aberration-corrected transmission electron microscopy and theoretical simulations, while other active species including Pd/Ni pure phase clusters and Pd/Ni single atoms obtained via metallene ball milling, also enhance the reaction. These findings present fundamental insights into active species identification and rational design of highly efficient hydrogen storage materials.

Ti3C2 and Ti2C MXene materials for high-performance isolation of extracellular vesicles via coprecipitation

Two-dimensional (2D) materials such as MXenes, are usually well utilized in the field of catalysts and battery due to their good hydrophilicity and diversified surface terminals. However, their potential applications in the treatment of biological samples have not been widely concerned. Extracellular vesicles (EVs) contain unique molecular signatures and could be used as biomarkers for the detection of severe diseases such as cancer, as well as monitoring the therapeutic response. In this work, two kinds of MXene materials (Ti₃C₂ and Ti₂C) were successfully synthesized and employed in the isolation of EVs from the biological samples by taking advantage of the affinity interaction between the titanium (Ti) in MXenes and the phospholipid membrane of EVs. Compared with Ti₂C MXene materials, TiO₂ beads and the other EVs isolation methods, Ti₃C₂ MXene materials exhibited excellent isolation performance via the coprecipitation with EVs due to the abundant unsaturated coordination of Ti²⁺/Ti³⁺, and the dosage of materials was the lowest. Meanwhile, the whole isolation process could be done within 30 min and integrated well with the following analysis of proteins and ribonucleic acids (RNAs), which was also convenient and economic. Furthermore, the Ti₃C₂ MXene materials were used to isolate the EVs from the blood plasma of colorectal cancer (CRC) patients and healthy donors. Proteomics analysis of EVs showed that 67 proteins were up-regulated, in which most of them were closely related to CRC progression. These findings indicate that the MXene material-based EVs isolation method via coprecipitation provides an efficient tool for early diagnosis of diseases.

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-TiNbCT_x) nanostructure to solve these problems. The on-set dehydrogenation temperature of MGH@d-TiNbCT_x 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.

Room-Temperature Transient Hydrogen Uptake of MgH2 Induced by Nb-Doped TiO2 Solid-Solution Catalysts

The practical applications of MgH₂ as a high-density hydrogen carrier depend heavily on efficient and low-cost catalysts to accelerate the dehydriding/hydriding reactions at moderate temperatures. In the present work, this issue is addressed by synthesizing Nb-doped TiO₂ solid-solution-type catalysts that dramatically improve the hydrogen sorption performances of MgH₂. The catalyzed MgH₂ can absorb 5 wt % of H₂ even at room temperature for 20 s, release 6 wt % of H₂ at 225 °C within 12 min, and the complete dehydrogenation can be achieved at 150 °C under a dynamic vacuum atmosphere. Density functional theory calculations reveal that Nb doping introduces Nb 4d orbitals with stronger interaction with H 1s into the density of states of TiO₂. This considerably enhances both the adsorption and dissociation ability of the H₂ molecule on the catalysts surface and the hydrogen diffusion across the specific Mg/Ti(Nb)O₂ interface. The successful implementation of solid solution-type catalysts in MgH₂ offers a demonstration and inspiration for the development of high-performance catalysts and solid-state hydrogen storage materials.

Nanostructuring of Mg-Based Hydrogen Storage Materials: Recent Advances for Promoting Key Applications

A comprehensive discussion of the recent advances in the nanostructure engineering of Mg-based hydrogen storage materials is presented. The fundamental theories of hydrogen storage in nanostructured Mg-based hydrogen storage materials and their practical applications are reviewed. The challenges and recommendations of current nanostructured hydrogen storage materials are pointed out.

Abstract

With the depletion of fossil fuels and global warming, there is an urgent demand to seek green, low-cost, and high-efficiency energy resources. Hydrogen has been considered as a potential candidate to replace fossil fuels, due to its high gravimetric energy density (142 MJ kg−1), high abundance (H2O), and environmental-friendliness. However, due to its low volume density, effective and safe hydrogen storage techniques are now becoming the bottleneck for the "hydrogen economy". Under such a circumstance, Mg-based hydrogen storage materials garnered tremendous interests due to their high hydrogen storage capacity (~ 7.6 wt% for MgH2), low cost, and excellent reversibility. However, the high thermodynamic stability (ΔH =  − 74.7 kJ mol−1 H2) and sluggish kinetics result in a relatively high desorption temperature (> 300 °C), which severely restricts widespread applications of MgH2. Nano-structuring has been proven to be an effective strategy that can simultaneously enhance the ab/de-sorption thermodynamic and kinetic properties of MgH2, possibly meeting the demand for rapid hydrogen desorption, economic viability, and effective thermal management in practical applications. Herein, the fundamental theories, recent advances, and practical applications of the nanostructured Mg-based hydrogen storage materials are discussed. The synthetic strategies are classified into four categories: free-standing nano-sized Mg/MgH2 through electrochemical/vapor-transport/ultrasonic methods, nanostructured Mg-based composites via mechanical milling methods, construction of core-shell nano-structured Mg-based composites by chemical reduction approaches, and multi-dimensional nano-sized Mg-based heterostructure by nanoconfinement strategy. Through applying these strategies, near room temperature ab/de-sorption (< 100 °C) with considerable high capacity (> 6 wt%) has been achieved in nano Mg/MgH2 systems. Some perspectives on the future research and development of nanostructured hydrogen storage materials are also provided.

Graphical Abstract

Honeycomb ZrCo Intermetallic for High Performance Hydrogen and Hydrogen Isotope Storage

Hydrogen isotope storage materials are of great significance for controlled nuclear fusion, which is promising to provide unlimited clean and dense energy. Conventional storage materials of micrometer-sized polycrystalline ZrCo alloys prepared by the smelting method suffer from slow kinetics, pulverization, disproportionation, and poor cycling stability. Here, we synthesize a honeycomb-structured ZrCo composed of highly crystalline submicrometer ZrCo units using electrospray deposition and magnesiothermic reduction. Compared with conventional ones, honeycomb ZrCo does not require activation and exhibits more than 1 order of magnitude increase in kinetic property. Owing to low defects and low stress, the anti-disproportionation ability and cycling stability of honeycomb ZrCo are also obviously higher than those of conventional ZrCo. Moreover, the interfacial stress (due to hydrogenation/dehydrogenation) as a function of particle radius is established, quantitatively elucidating that small-sized ZrCo reduces stress and pulverization. This study points out a direction for the structural design of ZrCo alloy with high-performance hydrogen isotope storage.

Solar-Driven Reversible Hydrogen Storage

The lack of safe and efficient hydrogen storage is a major bottleneck for large-scale application of hydrogen energy. Reversible hydrogen storage of light-weight metal hydrides with high theoretical gravimetric and volumetric hydrogen density is one ideal solution but requires extremely high operating temperature with large energy input. Herein, taking MgH₂ as an example, a concept is demonstrated to achieve solar-driven reversible hydrogen storage of metal hydrides via coupling the photothermal effect and catalytic role of Cu nanoparticles uniformly distributed on the surface of MXene nanosheets (Cu@MXene). The photothermal effect of Cu@MXene, coupled with the "heat isolator" role of MgH₂ indued by its poor thermal conductivity, effectively elevates the temperature of MgH₂ upon solar irradiation. The "hydrogen pump" effect of Ti and TiH_x species that are in situ formed on the surface of MXene from the reduction of MgH₂ , on the other hand, plays a catalytic role in effectively alleviating the kinetic barrier and hence decreasing the operating temperature required for reversible hydrogen adsorption and desorption of MgH₂ . Based on the combination of photothermal and catalytic effect of Cu@MXene, a reversible hydrogen storage capacity of 5.9 wt% is achieved for MgH₂ after 30 cycles using solar irradiation as the only energy source.

Cell Membrane and V2C MXene-Based Electrochemical Immunosensor with Enhanced Antifouling Capability for Detection of CD44

The inactive adsorption and interference of biomolecules in electrochemical biosensors is a topic of intense interest. Directly utilizing native cell membranes to endow electrochemical surfaces with antifouling and biocompatible features is a promising strategy, rather than attempting to synthetically replicate complex biological interface properties. In this study, we present a facial and sensitive sandwich-type antifouling immunoassay through platelet membrane/Au nanoparticle/delaminated V₂C nanosheet (PM/AuNPs/d-V₂C)-modified electrode as the substrate of sensing interface and methylene blue/aminated metal organic framework (MB@NH₂-Fe-MOF-Zn) as an electrochemical signal probe. The biosensor perfectly integrates the high conductivity of AuNPs-loaded V₂C MXene with the excellent loading property of NH₂-Fe-MOF-Zn to improve the electrochemical sensing performance. In addition, the excellent antifouling properties of the homogeneous cell membrane can effectively prevent the non-specific adsorption of model proteins. The obtained antifouling biosensor possesses the capability of ultrasensitive detection of CD44 and CD44-positive cancer cell in complex liquids and exhibits good analytical performance for the analysis of CD44 with a linear range from 0.5 ng/mL to 500 ng/mL. This strategy of developing cell membrane-based biosensing systems with enhanced antifouling capability can be easily expanded to the construction of other complex biosensors, and the advanced biological probes and analytical methods provide a favorable means to accurately quantify biomarkers associated with tumor progression.

Directed Stabilization by Air-Milling and Catalyzed Decomposition by Layered Titanium Carbide Toward Low-Temperature and High-Capacity Hydrogen Storage of Aluminum Hydride

AlH₃ is a metastable hydride with a theoretical hydrogen capacity of 10.01 wt % and is very easy to decompose during ball milling especially in the presence of many catalysts, which will lead to the attenuation of the available hydrogen capacity. In this work, AlH₃ was ball milled in air (called "air-milling") with layered Ti₃C₂ to prepare a Ti₃C₂-catalyzed AlH₃ hydrogen storage material. Such air-milled and Ti₃C₂-catalyzed AlH₃ possesses excellent hydrogen storage performances, with a low initial decomposition temperature of just 61 °C and a high hydrogen release capacity of 8.1 wt %. In addition, 6.9 wt % of hydrogen can be released within 20 min at constantly 100 °C, with a low activation energy as low as 40 kJ mol^-1. Air-milling will lead to the formation of an Al₂O₃ oxide layer on the AlH₃ particles, which will prevent continuous decomposition of AlH₃ when milling with active layered Ti₃C₂. The layered Ti₃C₂ will grip on and intrude into the AlH₃ particle oxide layers and then catalyze the decomposition of AlH₃ during heating. The strategy employing air-milling as a synthesis method and utilizing layered Ti₃C₂ as a catalyst in this work can solve the key issue of severe decomposition during ball milling with catalysts economically and conveniently and thus achieve both high-capacity and low-temperature hydrogen storage of AlH₃. This air-milling method is also effective for other active catalysts toward both reducing the decomposition temperature and increasing the available hydrogen capacity of AlH₃.

Synergistic Effect of a Facilely Synthesized MnV2O6 Catalyst on Improving the Low-Temperature Kinetic Properties of MgH2

While magnesium hydride (MgH2) has drawn considerable attention as a promising hydrogen storage material, it suffers from sluggish kinetics and high desorption temperature, hindering potential applications. Herein, we show that the hydrogen desorption kinetics of MgH2 can be significantly improved using bimetallic oxide MnV2O6 as the catalyst. A MgH2-MnV2O6 composite was prepared by a high-energy ball milling method. The results showed that the MgH2-MnV2O6 composite can release 5.57 wt % hydrogen within 10 min under 250 °C. The dehydrogenated MgH2-MnV2O6 sample can absorb 3.09 wt % hydrogen within 10 min under 50 °C. Notably, the reversible hydrogen storage property did not degrade at least within 100 cycles, showing excellent cycle stability. X-ray diffraction and transmittance electron microscopy measurements revealed that MnV alloy and V2O3 phases were formed during the ball milling process, leading to the synergistic catalytic effect. We argue that the bimetallic MnV alloy plays key catalytic roles in this system because MnV alloy can promote the fracture of the H-H and Mg-H bonds, significantly improving the hydrogen storage kinetics and low-temperature reversible hydrogen storage performance of MgH2.

Impact of Polymers on Magnesium-Based Hydrogen Storage Systems

In the present scenario, much importance has been provided to hydrogen energy systems (HES) in the energy sector because of their clean and green behavior during utilization. The developments of novel techniques and materials have focused on overcoming the practical difficulties in the HES (production, storage and utilization). Comparatively, considerable attention needs to be provided in the hydrogen storage systems (HSS) because of physical-based storage (compressed gas, cold/cryo compressed and liquid) issues such as low gravimetric/volumetric density, storage conditions/parameters and safety. In material-based HSS, a high amount of hydrogen can be effectively stored in materials via physical or chemical bonds. In different hydride materials, Mg-based hydrides (Mg–H) showed considerable benefits such as low density, hydrogen uptake and reversibility. However, the inferior sorption kinetics and severe oxidation/contamination at exposure to air limit its benefits. There are numerous kinds of efforts, like the inclusion of catalysts that have been made for Mg–H to alter the thermodynamic-related issues. Still, those efforts do not overcome the oxidation/contamination-related issues. The developments of Mg–H encapsulated by gas-selective polymers can effectively and positively influence hydrogen sorption kinetics and prevent the Mg–H from contaminating (air and moisture). In this review, the impact of different polymers (carboxymethyl cellulose, polystyrene, polyimide, polypyrrole, polyvinylpyrrolidone, polyvinylidene fluoride, polymethylpentene, and poly(methyl methacrylate)) with Mg–H systems has been systematically reviewed. In polymer-encapsulated Mg–H, the polymers act as a barrier for the reaction between Mg–H and O2/H2O, selectively allowing the H2 gas and preventing the aggregation of hydride nanoparticles. Thus, the H2 uptake amount and sorption kinetics improved considerably in Mg–H.

Efficient catalytic effect of the page-like MnCo2O4.5 catalyst on the hydrogen storage performance of MgH2

MnCo2O4.5 is decomposed into a variety of catalytically active substances during the de/hydrogenation process, which greatly promotes the hydrogen storage performance of MgH2.

Nanoconfined and in Situ Catalyzed MgH2 Self-Assembled on 3D Ti3C2 MXene Folded Nanosheets with Enhanced Hydrogen Sorption Performances

MXenes are considered as potential support materials for nanoconfinement of MgH₂/Mg to improve the hydrogen storage properties. However, it has never been realized so far due to the stacking and oxidation problems caused by unexpected surface terminations (-OH, -O, etc.) on MXenes. In this study, hexadecyl trimethylammonium bromide was used to build a 3D Ti₃C₂T_x architecture of folded nanosheets to reduce the stacking risk of flakes, and a bottom-up self-assembly strategy was successfully applied to synthesize ultradispersed MgH₂ nanoparticles anchored on the surface of the annealed 3D Ti₃C₂T_x (Ti-MX). The composite with a 60 wt % loading of MgH₂ NPs, 60MgH₂@Ti-MX, starts to decompose at 140 °C and is capable of releasing 3.0 wt % H₂ at 150 °C within 2.5 h. In addition, a reversible capacity up to 4.0 wt % H₂ was still maintained after 60 cycles at 200 °C without obvious loss in kinetics. In situ high-resolution TEM observations of the decomposition process together with other analyses revealed that the nanosize effect caused by the nanoconfinement and the multiphasic interfaces between MgH₂(Mg) and Ti-MX, especially the in situ formed catalytic TiH₂, were main reasons accounting for the superior hydrogen sorption performances.

Co-Addition of Mg2Si and Graphene for Synergistically Improving the Hydrogen Storage Properties of Mg-Li Alloy

Mg−Li alloy possesses a high hydrogen capacity. However, the hydrogenation and dehydrogenation performances are still far from practical application. In this work, Mg₂Si (MS) and graphene (G) were employed together to synergistically improve the hydrogen storage properties of Mg−Li alloy. The structures of the samples were studied by XRD and SEM methods. The hydrogen storage performances of the samples were studied by nonisothermal and isothermal hydrogenation and dehydrogenation, thermal analysis, respectively. It is shown that the onset dehydrogenation temperature of Mg−Li alloy was synergistically reduced from 360°C to 310°C after co-addition of Mg₂Si and graphene. At a constant temperature of 325°C, the Mg−Li−MS−G composite can release 2.7 wt.% of hydrogen within 2 h, while only 0.2 wt.% of hydrogen is released for the undoped Mg−Li alloy. The hydrogenation activation energy of the Mg−Li−MS−G composite was calculated to be 86.5 kJ mol⁻¹. Microstructure and hydrogen storage properties studies show that graphene can act as a grinding aid during the ball milling process, which leads to a smaller particle size for the composites. This work demonstrates that coaddition of Mg₂Si and graphene can synergistically improve the hydrogen storage properties of Mg−Si alloy and offers an insight into the role of graphene in the Mg−Li−MS−G composite.

The Improvement in Hydrogen Storage Performance of MgH2 Enabled by Multilayer Ti3C2

MgH₂ has become a hot spot in the research of hydrogen storage materials, due to its high theoretical hydrogen storage capacity. However, the poor kinetics and thermodynamic properties of hydrogen absorption and desorption seriously hinder the development of this material. Ti-based materials can lead to good effects in terms of reducing the temperature of MgH₂ in hydrogen absorption and desorption. MXene is a novel two-dimensional transition metal carbide or carbonitride similar in structure to graphene. Ti₃C₂ is one of the earliest and most widely used MXenes. Single-layer Ti₃C₂ can only exist in solution; in comparison, multilayer Ti₃C₂ (ML-Ti₃C₂) also exists as a solid powder. Thus, ML-Ti₃C₂ can be easily composited with MgH₂. The MgH₂+ML-Ti₃C₂ composite hydrogen storage system was successfully synthesized by ball milling. The experimental results show that the initial desorption temperature of MgH₂-6 wt.% ML-Ti₃C₂ is reduced to 142 °C with a capacity of 6.56 wt.%. The E_a of hydrogen desorption in the MgH₂-6 wt.% ML-Ti₃C₂ hydrogen storage system is approximately 99 kJ/mol, which is 35.3% lower than that of pristine MgH₂. The enhancement of kinetics in hydrogen absorption and desorption by ML-Ti₃C₂ can be attributed to two synergistic effects: one is that Ti facilitates the easier dissociation or recombination of hydrogen molecules, while the other is that electron transfer generated by multivalent Ti promotes the easier conversion of hydrogen. These findings help to guide the hydrogen storage properties of metal hydrides doped with MXene.

The Catalytic Role of D-block Elements and Their Compounds for Improving Sorption Kinetics of Hydride Materials: A Review

The goal of finding efficient and safe hydrogen storage material motivated researchers to develop several materials to fulfil the demand of the U.S. Department of Energy (DOE). In the past few years, several metal hydrides, complex hydrides such as borohydrides and alanates, have been researched and found efficient due to their high gravimetric and volumetric density. However, the development of these materials is still limited by their high thermodynamic stability and sluggish kinetics. One of the methods to improve the kinetics is to use catalysts. Among the known catalysts for this purpose, transition metals and their compounds are known as the leading contender. The present article reviews the d-block transition metals including Ni, Co, V, Ti, Fe and Nb as catalysts to boost up the kinetics of several hydride systems. Various binary and ternary metal oxides, halides and their combinations, porous structured hybrid designs and metal-based Mxenes have been discussed as catalysts to enhance the de/rehydrogenation kinetics and cycling performance of hydrogen storage systems.

Study of the Hydrogen Storage Properties and Catalytic Mechanism of a MgH2-Na3AlH6 System Incorporating FeCl3

In this work, the catalytic effects of FeCl₃ toward the hydrogen storage properties of the MgH₂-Na₃AlH₆ composite were investigated for the first time. The temperature-programed desorption results indicated that the onset temperature of the hydrogen release of a 10 wt % FeCl₃-doped MgH₂-Na₃AlH₆ composite was ∼30 °C lower than that of the undoped MgH₂-Na₃AlH₆ composite. The addition of FeCl₃ into the MgH₂-Na₃AlH₆ composite resulted in improved absorption and desorption kinetics performance. The absorption/desorption kinetics measurements at 320 °C (under 33 and 1 atm hydrogen pressure, respectively) indicated that within 10 min, the doped sample absorbed ∼4.0 wt % and desorbed ∼1.5 wt % hydrogen. By comparison, the undoped sample absorbed only ∼2.1 wt % and desorbed only ∼0.6 wt % hydrogen under the same conditions and time. Comparably, the apparent activation energy value of the doped composite is 128 kJ/mol, which is 12 kJ/mol lower than that of the undoped composite (140 kJ/mol). The formation of the new species of MgCl₂ and Fe in the doped composite was detected from X-ray diffraction analysis after heating and absorption processes. These two components were believed to play a vital role in reducing the decomposition temperature and kinetics enhancement of the MgH₂-Na₃AlH₆ composite.

Enhanced Hydrogen Storage Performance of MgH2 by the Catalysis of a Novel Intersected Y2O3/NiO Hybrid

MgH2 is one of the most promising hydrogen storage materials due to its high hydrogen storage capacity and favorable reversibility, but it suffers from stable thermodynamics and poor dynamics. In the present work, an intersected Y2O3/NiO hybrid with spherical hollow structure is synthesized. When introduced to MgH2 via ball-milling, the Y2O3/NiO hollow spheres are crushed into ultrafine particles, which are homogenously dispersed in MgH2, showing a highly effective catalysis. With an optimized addition of 10 wt% of the hybrid, the initial dehydrogenation peak temperature of MgH2 is reduced to 277 °C, lowered by 109 °C compared with that of the bare MgH2, which is further reduced to 261 °C in the second cycle. There is ca. 6.6 wt% H2 released at 275 °C within 60 min. For the fully dehydrogenation product, hydrogenation initiates at almost room temperature, and a hydrogenation capacity of 5.9 wt% is achieved at 150 °C within 150 min. There is still 5.2 wt% H2 desorbed after 50 cycles at a moderate cyclic condition, corresponding to the capacity retention of 79.2%. The crystal structure and morphology of the Y2O3/NiO hybrid is well preserved during cycling, showing long-term catalysis to the hydrogen storage of MgH2. The Y2O3/NiO hybrid also inhibits the agglomeration of MgH2 particles during cycling, favoring the cyclic stability.