Recent advancements in TiFe alloy for solid-state hydrogen storage: From synthesis to performance

Abstract

This review delves into the advancements of TiFe alloy for solid-state hydrogen storage, highlighting its structure, properties, preparation method, and hydrogen storage performance. The impact of alloy composition and microstructure of the TiFe alloy upon the hydrogen storage kinetics were explored and summarized, as well as on hydrogen storage capacity. The work details the synthesis methods, from induction melting to mechanical alloying, and discusses strategies to enhance TiFe's hydrogen absorption/desorption rates and cycling stability. Emphasis is placed on the role of process control agents and nanostructuring in improving the hydrogen storage performance of TiFe alloy. This review underscores the potential of TiFe alloys in realizing a sustainable hydrogen economy and outlines challenges in activation conditions and cost reduction, providing a roadmap for future research directions.

Keywords

TiFe alloy hydrogen storage synthesis methods kinetics energy materials

Introduction

Driven by the global energy transition and the Sustainable Development Goals, the innovation and application of clean energy technology leads the frontier of science and technology economy.^1,2 Significant increase in research in the areas of renewable energy production, storage, distribution and end-use.³ Hydrogen, with its wide range of sources,⁴ zero-emission environmental properties,⁵ and renewable, high energy density,⁶ is recognized as an ideal candidate to replace fossil fuels.⁷^,⁸ The concept of the hydrogen economy envisages the replacement of fossil fuels with hydrogen to support the infrastructure of society's energy needs.^9–11 The efficient and safe storage of hydrogen energy is a key bottleneck for commercial application.¹²^,¹³ Therefore, the R&D and optimization of hydrogen storage materials have become the focus of research in the field of hydrogen energy.¹⁴

Hydrogen is the essential element having profound significance to the evolution of the solar system and the human's understanding of the physical world that is the simplest element in the universe, consisting of a single proton and an electron.Hydrogen, as a main group element, exhibits various states,Under standard conditions, it primarily exists as diatomic molecular hydrogen (H₂)，also including proton (H⁺), hydride (H⁻), and radical (H·) states.

Proton (H⁺) is a positively charged hydrogen ion. In aqueous solutions, hydrogen typically appears in the form of protons, such as in acids, where H⁺ ions are the main component. In addition to aqueous solutions, protons also exist in other environments. In plasmas, such as those within stars, hydrogen exists primarily in a plasma state, with protons being a major component. In certain chemical reactions, protons can act as catalysts or intermediates. For instance, in the protonation and deprotonation processes of biomolecules, protons play a vital role in regulating biological activities.Hydrides are compounds where hydrogen combines with other elements.

Compounds of hydrogen with less electronegative elements are known as hydrides. So, when hydrogen reacts with any other element, the product formed is considered to be a hydride. But hydride formation is not seen from Nitrogen group elements, and this condition is known as the hydride gap. Hydrogen molecule usually reacts with many elements except noble gases to form hydrides. However, the properties may vary depending on the type of intermolecular force that exists between the elements, their molecular masses, temperature, and other factors.Depending on the elements hydrogen bonds with and the type of chemical bonding, hydrides can be classified into three categories: ionic hydrides, covalent hydrides, and metallic hydrides.They are formed when hydrogen molecule reacts with highly electropositive s-block elements (Alkali metals and alkaline earth metals).

Ionic or Saline Hydrides are formed when hydrogen molecule reacts with highly electropositive s-block elements (Alkali metals and alkaline earth metals).

They do not dissolve in conventional solvents, and they are mostly used as bases or reducing reagents in organic synthesis.Covalent hydrides are formed when hydrogen reacts with other similar electronegative elements like Si, C, etc. The most common examples are CH₄ and NH₃.A hydrogen compound that forms a bond with another metal element is classified as a metal hydride. The bond is mostly covalent type, but sometimes the hydrides are formed with ionic bonds. These are usually formed by transition metals and are mostly non-stoichiometric, hard, high melting and boiling points.

A hydrogen radical (H·) is a neutral atom or molecule with an unpaired electron. In molecular hydrogen, the two hydrogen atoms share a pair of electrons to form a covalent bond. When this bond breaks homolytically, a hydrogen radical is formed. Hydrogen radicals are highly reactive and tend to quickly combine with other atoms or molecules. For example, in the reaction between hydrogen gas and chlorine gas under light, hydrogen radicals are generated, which then react with chlorine molecules to produce hydrogen chloride. Hydrogen radicals are significant in combustion processes. When hydrogen burns in oxygen, hydrogen radicals are produced, which further react with oxygen molecules to form water.

According to the classification of hydrogen storage state, it is generally divided into solid hydrogen storage,¹⁵ liquid hydrogen storage and gaseous hydrogen storage.¹⁶^,¹⁷ Solid-state hydrogen storage is known for its large capacity, safety and efficiency. Figure 1 illustrates various hydrogen storage technologies and their classifications.¹⁸ Among these, physical hydrogen storage encompasses methods such as compression, freezing, and liquefaction. In contrast, material-based hydrogen storage primarily involves metal hydride systems.^19,20 Metal hydride hydrogen storage offers several advantages over other methods, including enhanced safety, high hydrogen storage density, stable pressure conditions, and straightforward processes for hydrogen filling.²¹ Notably, the volumetric density of stored hydrogen in metal hydrides is approximately 1000 times greater than that of gaseous hydrogen under equivalent temperature and pressure conditions. Metal hydride hydrogen storage, as a promising hydrogen supply solution, offer several advantages. They have high bulk hydrogen density, ease of operation and transportation, low cost, good safety, and favorable reversible cycling performance. However, their low mass efficiency is a drawback.²² If this issue can be effectively addressed, metal hydride hydrogen storage could be highly suitable for fuel cell vehicles. In contrast, high-pressure gaseous hydrogen storage technology is more mature and currently the most commonly used method in China. Its benefits include low storage energy consumption, relatively low cost (especially at moderate pressures), and the ability to regulate hydrogen release via pressure reducing valves. Nevertheless, the pressurization process for hydrogen storage tanks is costly, and safety risks, such as leaks and explosions, increase with pressure.²³ Therefore, improving the safety and performance of high-pressure gaseous hydrogen storage is crucial.

Figure 1.

Technologies for hydrogen storages.

As the demand for hydrogen energy rises, technological innovation is imminent. The focus is on improving the performance of hydrogen storage materials, reducing costs and expanding commercialization.²⁴ Gregory J. Kubas²⁵ has found, by neutron diffraction structural analysis, that the H-H bond in the W(CO)₃(PR₃)₂(H₂) complex is laterally bonded to the metal (with a W-H distance of 1.89 Å), and that the H-H bond length is lengthened from 0.74 Å for the free H₂ to 0.82 Å. Also, H₂ can be reversibly removed in the complex to form a ligand-unsaturated precursor complex. The metal-hydrogen molecular system exhibits a rich dynamic behavior including rotation of H₂, isotopic exchange, exchange with a hydride ligand, and dissociation into two hydride ligands. This study not only changes the traditional understanding of metal-hydrogen bonding, but also has important implications for catalytic hydrogenation mechanisms and hydrogen storage.

The discovery that hydrogen can act as a ligand to form stable σ-bonded complexes with transition metals has overturned the traditional understanding of hydrogen-metal interactions and opened up a new field of research. The study of hydrogen coordination complexes not only helps to understand the activation and transformation of small molecules on metal centers, but also provides new ideas and possible solutions for practical applications such as energy storage, homo- and hetero-cleavage of acids.²⁶ Metal hydrides,²⁷ such as TiFe alloys,²⁸ have become a research hotspot in the field of solid-state hydrogen storage technology.²⁹ TiFe hydrogen storage alloy has high hydrogen storage performance and its hydrogen storage capacity can reach 1.86 wt.%.³⁰ which is an ideal hydrogen storage material. The reaction pressure of the TiFe alloy at room temperature³¹ (about 30°C) is 3 MPa. The achievable equilibrium pressure is 0.3 MPa, and the maximum mass (energy density) at room temperature is 1.86%,³² the slope of the hydrogen absorption and discharge platform of the alloy is small. In addition, Fe and Ti are abundant, lower cost,³³ which is very suitable for industrial hydrogen storage. There are much efforts to improve the hydrogen absorption and desorption kinetics, cycling stability and operating temperature range of TiFe-based alloys to meet the stringent requirements of different application scenarios, such as hydrogen storage in fuel cell vehicles, portable power systems, industrial gas storage, and grid scale energy buffering. This review paper focuses on TiFe-based hydrogen storage alloys. Focusing on the structure and properties of the hydrogen storage system, the preparation methods of TiFe hydrogen storage alloys in recent years are summarized and discussed. The influencing factors of hydrogen storage performance were analyzed. It is of theoretical and practical significance for the research and development and performance optimization of high-performance TiFe-based hydrogen storage alloys.

The structure and properties of the solid hydrogen storage alloy TiFe

Crystal structure of TiFe alloy

The TiFe binary alloy phase diagram³⁴ reveals that in the binary alloy system, TiFe and TiFe₂, exist as intermetallic compounds (Figure 2). TiFe₂ is a Cl4-Laves phase structure,³⁵ which does not react easily with hydrogen, and Ti₂Fe intermetallic compounds only appear when the temperature is higher than 2000 °C. When the temperature is lower than 1000 °C, Ti₂Fe can only exist as TiFe and Ti monomers.³⁶ From the point of view of practical applications, TiFe₂ does not have hydrogen storage properties.

Figure 2.

Phase diagram of TiFe binary alloy.

The crystal structure of the TiFe alloy has a CsCl-type structure,³⁷ and the space group is PM3 m³⁸ with a lattice constant of a = 0.2976 nm.^39,40 TiFe alloy, as a typical hydrogen storage alloy, has unique crystal structure and chemical composition. It mainly includes the following points. Fixed melting point; Anisotropy; A polyhedral shape that spontaneously presents a certain symmetry. Normal valence compound composition is fixed, can be expressed by chemical formula, generally AB type.⁴¹ Each cell contains three flattened octahedral voids, and each octahedral void can be divided into four deformed tetrahedral voids. Each tetrahedral void is made up of two atoms of A and two atoms of B. Although there are more tetrahedral voids in AB hydrogen storage alloys, hydrogen can only partially occupy the tetrahedral voids.⁴² This is mainly because it is limited by Shoemaker's fill incompatibility rules. The hydrogen atoms entering the TiFe alloy are located only in the center of the regular octahedron surrounded by two iron atoms and four titanium atoms.⁴³

Physical and chemical properties of TiFe alloy

The main physical and chemical properties of TiFe alloy are listed in Table 1. Thermal stability and melting point. The high thermal stability of TiFe alloy ensures its stable structure and reliable performance under a wide range of high temperature conditions, and has broad prospects in high temperature applications. The melting point reaches 1320 ° C,⁴⁴ ensuring excellent performance at extremely high temperatures.

Table 1.

Physical and chemical properties of TiFe alloy.

Attribute	Condition	Description
Melting Point	/	1320°C
Compressive Strength	Ti-₁₅Fe Alloy, Room Temperature	2702 MPa
Elastic Modulus	Ti-₁₅Fe Alloy, Room Temperature	64,600 MPa
Compressive Yield Strength	Ti-₆₅Fe₃₅ Alloy, Room Temperature	1800 MPa
Peak Strength	Ti-₆₅Fe₃₅ Alloy, Room Temperature	2220 MPa

Mechanical properties and strength. TiFe alloys exhibit excellent mechanical properties, including high strength and toughness. Studies have shown that Ti₋₁₅Fe alloy has a compressive strength of 2702 MPa and an elastic modulus of 64,600 MPa at room temperature.⁴⁵ The compressive yield strength of Ti₋₆₅Fe₃₅ alloy at room temperature is 1800 MPa, and the peak strength is 2220MPa.⁴⁶ These properties are due to its unique crystal structure and the interaction between alloying elements. At the same time, TiFe alloy has excellent ductility and fatigue resistance, which ensures the integrity and functional stability of the structure under complex stress environment, and maintains continuous working efficiency.

The hydrogen storage properties of TiFe hydrogen storage alloys are significantly affected by thermal stability, mechanical and physical properties. Thermal stability determines the structural and property stability of the alloy at different temperatures, affecting its hydrogen absorption/release efficiency and cycle life. Mechanical properties such as strength and toughness affect the durability and reliability of the alloy in practical applications, and alloys with high strength and good toughness are less susceptible to damage during cycling. Physical properties such as density, electrical and thermal conductivity affect hydrogen diffusion and storage efficiency in alloys, e.g., low-density alloys can increase the specific energy density of hydrogen storage systems. Synergistic optimization of these properties can significantly improve the hydrogen storage efficiency and practical application potential of TiFe alloys.⁴⁷

Material preparation methods of TiFe alloy for solid hydrogen storage 3.1 melting method

Induction melting is the main method for preparing TiFe alloys.⁴⁸ This method can quickly deal with a large number of raw materials, quickly realize the melting of metals or alloys, suitable for large-scale production, melting process technology is mature, easy to apply and control in large scale production, equipment requirements are relatively simple, process control is direct, with obvious cost effective. However, despite these economic advantages, the induction melting process has some significant disadvantages. Induction melting requires the metal to be heated to a high temperature, which is energy intensive to maintain. The thermal efficiency of the melting equipment is not 100% and there are problems such as heat loss, resulting in wasted energy, which may offset some of the cost advantages. The structure of the alloys formed by this method is difficult to control accurately and may lead to inconsistent alloy properties. In addition, reactions between the molten metal and the crucible material can occur, and small amounts of crucible material may melt into the alloy. This contamination can reduce the purity of the TiFe alloy.^49,50

In this method, the melt homogenization is promoted by medium and high frequency induction heating and electromagnetic stirring in an inert atmosphere, and the homogeneous TiFe alloy can be prepared. Induction smelting method uses high purity titanium and iron as raw materials, according to a certain stoichiometric ratio to mix. The prepared raw material is put into the vacuum arc melting furnace, and kept at the appropriate melting temperature for a certain time, so that titanium and iron are fully melted and alloyed. After smelting is complete, turn off the power and let the alloy ingot cool naturally in the furnace. After the alloy ingot has cooled to room temperature, it is removed for subsequent treatment, as shown in Table 2. Subsequently, the ingot obtained by smelting was analyzed and tested. However, the reaction of the molten metal with the crucible material affects the purity of the alloy and requires multiple cycles of activation at 450°Cand 5 MPa hydrogen pressure.^51–53 Compared with the mechanical alloying method, the activation process of induction melting method is more complicated and the conditions are more stringent.

Table 2.

Experimental data of TiFe prepared by smelting method.

Experiment number	Raw material purity（Ti/Fe）	Stoichiometric ratio（Ti:Fe）	Melting temperature（°C）	Melting time（min）	Vacuum （Pa）	Cooling metho	Crystal size (nm)	Purity	Hydrogen storage performance（wt%）
1	99.9%/99.9%	1:1	1600	20	10⁻⁴	Natural cooling	5 × 5 × 5	98%	1.5
2	99.95%/99.95%	1.05：1	1700	25	5 × 10⁻⁴	Control cooling	6 × 6 × 6	98.50%	1.6
3	99.9%/99.9%	0.95：1	1550	18	8 × 10⁻⁴	Natural cooling	4 × 4 × 4	97.50%	1.4
4	99.98%/99.98%	1：1	1650	22	2 × 10⁻⁴	Control cooling	5.5 × 5.5 × 5.5	99%	1.7
5	99.92%/99.92%	1：0.9	1500	15	6 × 10⁻⁴	Natural cooling	4.5 × 4.5 × 4.5	97%	1.3

By X-ray diffraction (XRD), it is found that the grain size of the alloy is uniform and the grain boundary is clear. Further performance tests show that the TiFe alloy has good hydrogen storage performance, and its hydrogen storage capacity reaches the expected target. Dematteis and co-authors reported the development of Ti-Fe-Mn ternary alloys through induction melting, followed by annealing and quenching processes.⁵⁴ The as-prepared TiFe_0.85Mn_0.05 alloy exhibited a hydrogen capacity of 1.73wt%, and it can be activated at 25°C under a hydrogen pressure of 2.5 MPa. Barale and co-authors conducted a study on the TiFe_0.85Mn_0.05 alloy for hydrogen storage applications through induction melting.⁵⁵ A 5 kg batch of this alloy demonstrated a hydrogen storage capacity of 1.0 wt% H₂ at 55 °C, with its sorption properties remaining stable over 250 cycles. It was found that the homogeneity of the alloy could be improved by increasing the melting temperature properly, while the volatilization of some elements could be caused by excessive temperature. Extending the melting time is conducive to the full reaction of the alloy, but excessive extension will increase energy consumption and cost. The adjustment of the ratio of raw materials has a significant effect on the composition and properties of the alloy, and optimizing the ratio of raw materials can improve the comprehensive properties of the alloy.

Mechanical alloying method

The mechanical alloy method enables TiFe alloying at room temperature. The mechanical alloying method can enhance the hydrogen absorption and desorption properties of the alloy by mechanical deformation of the powder to improve the specific surface area, activity and internal defects.⁵⁶ TiFe alloy prepared by mechanical alloy method has the advantages of large hydrogen storage capacity, easy activation, fast hydrogen absorption and release rate and simple process.⁵⁷ However, fresh surface activity is too high, easy to oxidation passivation at room temperature, rapid loss of hydrogen absorption capacity, and the use of high-purity raw materials lead to high costs. These two points seriously restrict its industrial application. Nevertheless, this method still opens up a new path for the preparation of high-performance TiFe crystals.

The process of preparing TiFe alloy by mechanical alloy method can be generally divided into the following five stages. (1)Ti and Fe metal particles are flattened in the early stage of ball milling, forming Ti and Fe layered structures; (2) Cold welding occurs in Ti and Fe of layered structure;⁵⁸ (3) The Ti and Fe composite structure is continuously refined and crimped to form a spiral structure; (4) the healing and fracture reached a balance, and the particle size remained stable; (5) Finally, the Ti-Fe alloy powder is mixed evenly and reacts at the atomic level to form an amorphous equilibrium product with a nanostructure.

High purity titanium powder and iron powder were used as raw materials for TiFe preparation by mechanical alloy method, and mechanical alloying was carried out by planetary ball mill. The titanium powder and iron powder are mixed according to a certain atomic ratio, put into the ball mill tank, and add the grinding ball and process control agent. Adjust the speed and interval of the ball mill. Different ball grinding times (e.g., 10, 20, 30 h, and etc.) were set to study their effects on crystal formation.⁵⁹ In high energy ball milling, with the extension of milling time, the energy transferred by the ball to the powder through collision and extrusion increases continuously, resulting in a series of remarkable phase transformation processes of the mixed powder. After the ball milling, the sample is put into a vacuum drying oven and dried at the appropriate temperature to remove the adsorbed water and gas. The specific results is shown in Table 3.

Table 3.

Structure and performance parameters of TiFe prepared by mechanical alloy method.

Experiment number	Ball mill time	Pellet ratio	Process control agents	Ball mill speed（rpm）	Ti/Fe atomic ratio	Average crystal size（nm）	Hydrogen storage capacity (wt%）	Hydrogen uptake rate (wt%/min)	Hydrogen release rate（wt%/min)
1	20	10：01	ethanol	300	1：1	50	1.5	0.2	0.15
2	30	5：01	n-hexane	350	1：1.1	40	1.6	0.25	0.18
3	25	12：01	isopropanol	400	0.9 : 1	45	1.45	0.22	0.16
4	35	18：01	Absolute ethanol	450	1.05 : 1	35	1.7	0.28	0.2
5	28	14：01	acetone	500	1.95；1	42	1.55	0.23	0.17

Mechanical alloying depends on energy conversion during ball milling, and collision frequency and energy are crucial. The process parameters, such as medium, atmosphere, speed, pellet ratio and time, all affect the alloying process by adjusting these two factors. In addition, process control agents can affect the process of mechanical alloying. Falcao and co-authors performed the mechanical alloying of TiFe using different organic Process Control Agents (PCAs), such as ethanol, stearic acid, low-density polyethylene, benzene, and cyclohexane.⁶⁰ Cold welding can be controlled by the addition of PCAs (10 wt% or over) and replacing Ti with fragile TiH₂, the as-produced TiFe exhibit yields ranging from 90–95 wt%. After subjecting the milled samples to post-heating at 873 K under vacuum conditions, the alloy demonstrated a maximum hydrogen capacity of 0.94 wt% at room temperature. Vega and co-authors propose a method by using a pre-milled vessel with stearic acid as PCAs.⁶¹ Nanocrystalline TiFe was synthesized in this way with low oxygen contamination, and full yields for milling time of 6 h or longer, requiring no heat treatments for the first hydrogen absorption. The hydrogen storage capacity of 1.0 wt% at room temperature under 2 Mpa was attained by the sample milled for 6 h.

Hydride cycle

In IChPh of Armenian National Academy of Sciences, a principally new technique based on a high efficiency “hydride cycle” is elaborated for receiving the alloys of refractory metals.⁶² Compared to conventional methods, the Hydride cycle (HC) method offers important advantages over conventional alloy production methods: low energy consumption, simple equipment, and short alloy formation times. The method is based on metal hydrides as precursor materials. The alloy formation process takes place at a temperature of about 1000°C between two (or more) metal hydrides or between a metal hydride and a pure metal. For the production of alloys by the HC method, metal hydrides synthesized by the self-spreading high temperature synthesis (SHS) method are used as starting materials.⁶³

Davit Mayilyan and co-authors first used the unconventional “Hydride Cycle” method to produce TiFe and [TiFe + 4 wt%] Zr alloys, using TiH₂ and ZrH₂ as precursors.⁶⁴ XRD analysis determined the crystal structure and lattice parameters, while Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer studied the microstructure. The alloys contained Fe₂Ti and TiFe phases. The study investigated the first hydrogenation of these alloys via different processes, finding that compacted pellets could react with hydrogen without pre-crushing. Regardless of composition and hydrogen pressure, SHS combustion temperatures for the alloys were 80–150°C, and the reactions were reversible. Conventional high-pressure first hydrogenation of [TiFe + 4 wt% Zr] gave the best hydrogen absorption capacity (1.52 wt%). Figure 3 shows Thermogravimetry Analysis (TGA) curve of TiFe + 4 wt % Zr alloy sample hydrogenated by conventional processat room temperature.

Figure 3.

TGA and DTA curves of TiFe + 4 wt % Zr hydrogenated alloy.

Aleksanyan and co-authors achieved the synthesis of Ti₆Al₄V alloy from TiH₂ and Hydride of V (VH) hydrides via a developed HC method, uncovering the alloy's formation mechanism.⁶⁵ The study explored the synthesis possibility and established the formation and structure phase mechanisms during continuous hydrogen concentration changes in TiH₂ and VH hydrides, based on dehydrogenation sintering conditions. Experimentally, using TiH₂ and VH powders as starters, Ti₆Al₄V alloy formed at 1000–1050 °C through rapid solid-phase interaction. Within the α→β polymorphic transformation temperature range, an α+β two - phase alloy emerged. Additionally, the SHS synthesis of Ti₆Al₄VHx hydride was demonstrated. Like TiH₂, it's an un-sintered, highly porous, easily dispersible product with high hydrogen content. Figure 4 is the Differential Thermal Analysis (DTA) of the [TiH2 + 6Al + 4VH] charge and Ti₆Al₄VH_1.606 hydride of alloy.

Figure 4.

The DTA of the TiH₂ + 6Al + 4VH and Ti₆Al₄VH_1.606.

Aleksanyan and co-authors explored the formation mechanism of ternary alloys in the Ti-V-Mn system via the “hydride cycle” method, synthesizing TiV_1.2Mn_0.8, TiV_0.8Mn_1.2, and Ti_0.37V_0.25Mn_0.25 alloys.⁶⁶ Their interaction with hydrogen was examined in combustion mode and at 25–50 °C post short term activation. X-ray, DTA (Figure 5), and chemical analysis revealed that both modes yielded hydrides with identical structures, hydrogen contents, and thermal properties: TiV_1.2Mn_0.8H_3.7, TiV_0.8Mn_1.2H_2.35, and Ti_0.37V_0.25Mn_0.25H_1.56. These hydrides remained stable during sorption - desorption cycles and long - term storage.

Figure 5.

The DTA curves of: a) 0.37TiH₂ + 0.38VH + 0.25Mn; b) Ti_0.37V_0.38Mn_0.25H_1.56.

Hydrogen storage properties of TiFe solid hydrogen storage alloy materials

First hydrogenation

Hydrogenation of TiFe hydride is the succession of first formation of α-solid solution TiFeH_0.1 followed by the TiFeH₁ monohydride (β) and dihydride TiFeH₂ (γ). Compared to other metals hydrides such as magnesium or body-centered cubic (BCC) alloys, its main advantage lies in the reversibility of hydrogen storage at room temperature. However, the first hydrogenation, the so-called activation process, is a lengthy and difficult operation because of the presence of a passivating oxidized surface. Therefore, before the first hydrogenation, the alloy usually needs to be prepared by submitting it to high temperature and hydrogen pressure. Reilly and co-authors reported that pure TiFe sample had to be exposed to high temperatures (about 400 °C) and high hydrogen pressures (6.5 MPa) before being able to absorb/desorb hydrogen at normal conditions.⁶⁷

Lv and co-authors studied the microstructure and initial hydrogenation characteristics of TiFe with 4 wt.% Zr addition, prepared by casting, ball milling, and cryomilling.⁶⁸ Figure 6 shows the first hydrogenation process at room temperature and under 4.5 MPa of hydrogen.Results show ball milling and cryomilling effectively reduce particle and crystallite sizes, mostly in the first 15 min. However, cryomilled samples have no hydrogen absorption capacity. Ball milling improves initial kinetics compared to ascast samples but reduces hydrogen storage capacity. This improvement is likely due to reduced crystallite size with increased milling time. Prolonged ball milling may cause capacity loss from new grain boundaries. Despite faster kinetics, the rate - limiting step remains unchanged, as all kinetic curves fit the 3D growth, diffusion - controlled model with decreasing interface velocity.

Figure 6.

First hydrogenation at room temperature and under 4.5 MPa hydrogen of the TiFe + 4 wt.% Zr alloy at different states.

Patel and co-authors studied how adding Zr + V or Zr + V + Mn to TiFe alloy affects its microstructure and hydrogen storage properties.⁶⁹ They found that adding only V doesn't produce enough secondary phase for room - temperature hydrogenation at 2 Mpa. But adding [2 wt.% Zr + 2 wt.% V or 2 wt.% Zr + 2 wt.% V + 2 wt.% ]Mn creates a fine Ti₂Fe like secondary phase. These alloys show fast initial hydrogenation and high capacity, with the rate limiting step being 3D growth, diffusion - controlled with decreasing interface velocity. This suggests Ti₂Fe like secondary phases may act as hydrogen gateways. Razafindramanana and co-authors studied the effect of adding hafnium to TiFe alloy on its hydrogenation process.⁷⁰ They synthesized TiFe + x Hf alloys (x = 0, 4, 8, 12, 16 wt.%) by arc melting and analyzed their microstructure using scanning electron microscopy and electron microprobe analysis. The alloys consisted of B2-TiFe, C14-Laves, and BCC phases. They found that at least 8 wt.% hafnium is needed to enhance the first hydrogenation. The material with this addition reaches maximum hydrogen capacity in under two hours at room temperature and 2 Mpa of hydrogen. Hafnium also lowers the plateau pressure in the pressure-composition isotherm, indicating a positive effect on TiFe's activation properties. Gosselin and co-authors of investigation was to improve the first hydrogenation of TiFe by adding yttrium.⁷¹ Figure 7 is first kinetics hydrogenation at room temperature and at a pressure of 2.5 MPa of hydrogen TiFe alloys + x wt.% Y .The compositions studied were TiFe + x wt.% Y with x = 4, 6, and 8. From electron microscopy it was found that all alloys were multiphase with a matrix of TiFe phase containing less than 0.4 wt.% of Y and a secondary phase rich in yttrium. When x increased, the chemical compositions of the matrix changed and the secondary phase changed. The sample with 8% of yttrium had the fastest kinetics. The hydrogen capacity increased with the amount of Y.

Figure 7.

First kinetics hydrogenation at room temperature and at a pressure of 2.5 MPa of hydrogen TiFe alloys + x wt.% Y for x = 4, 6, and 8.

Hydrogen storage capacity

The theoretical hydrogen storage mass fraction of TiFe alloy is about 1.86%, which has high hydrogen storage potential. The hydrogenation of TiFe results in the formation of one TiFe-H solid solution and two ternary hydrides: TiFeH_0.1, (α-phase, solid solution), TiFeH_1.04 (β-phase, hydride), and TiFeH_1.95 (γ-phase, hydride)_. The reactions which take place stepwise can be expressed as follows.⁷² From the chemical composition and reaction mechanism, the reaction of TiFe with hydrogen can be expressed as:

{TiFeH}_{0.1} + H_{2} ⇌ {TiFeH}_{1.04}

(1)

{TiFeH}_{1.04} + H_{2} ⇌ {TiFeH}_{1.95}

(2)

TiFe + H_{2} = {TiFeH}_{2}

(3)

The theoretical hydrogen storage mass fraction of TiFe alloy is based on the perfect chemical reaction and crystal structure. However, in practical application, it is often difficult to reach the theoretical level. In actual measurements, the hydrogen storage capacity of TiFe alloys is usually between 1.4% and 1.8%.

The hydrogen storage properties of TiFe alloy are affected by five factors. First, the purity of raw materials, impurities will affect hydrogen adsorption, reduce the actual hydrogen storage capacity. Second, the microstructure,⁷³ grain size and grain boundary⁷⁴ characteristics limit the adsorption and diffusion of hydrogen. The third is the surface state, the oxide layer will prevent hydrogen contact. The fourth is thermodynamics and kinetic.⁷⁵ The high energy barrier and the slow process of hydrogen atom diffusion inside the alloy result in the alloy failing to achieve the ideal hydrogen storage amount in the required time.⁷⁶ The fifth is the number of cycles, phase transition or fatigue resulting in hydrogen storage capacity attenuation.⁷⁷ These factors together determine the hydrogen storage efficiency of TiFe alloy.

The following methods are generally used to improve the hydrogen storage capacity of TiFe(Table 4) . (1) Optimize the alloy composition:^78,79 add Ni, Mn, Cr and other elements to form a multi-component alloy, improve the crystal and electronic structure, increase the hydrogen storage site, and improve the capacity. (2) Improve the microstructure:⁸⁰ refine the grains, increase the number of grain boundaries, and provide more hydrogen diffusion channels and adsorption sites. The preparation of nanostructures, such as nanocrystals, wires, tubes, etc., can significantly improve the hydrogen storage performance (3) Surface treatment to remove the surface oxide layer: chemical or physical methods are used to clean the oxide on the surface of the alloy to improve the contact between hydrogen and the active site. (4) Surface coating: Apply an appropriate coating, such as a precious metal coating (such as palladium), to promote hydrogen adsorption and desorption. (5) Optimize the preparation process, improve the melting and casting methods:⁸¹ control the cooling speed, hot processing conditions, etc., to obtain a more ideal organizational structure. (6) The use of advanced preparation technology: such as mechanical alloying, etc., to improve the uniformity and activity of the alloy. The composite material is constructed with carbon material, and the high specific surface area and good electrical conductivity of carbon material are used to enhance the hydrogen storage performance. (7) Pretreatment: hydrogenation pretreatment is performed on the alloy to improve its subsequent hydrogen storage performance.

Table 4.

Methods to improve the hydrogen storage capacity of TiFe.

Method	Feature
Optimize alloy composition	Improve the crystal and electronic structures, increase hydrogen storage sites, and boost hydrogen storage capacity.
Improve microstructure	Provide more hydrogen diffusion channels and adsorption sites Nanostructures can significantly improve hydrogen storage performance
Surface Treatment	Remove the oxide layer on the surface of the alloy and improve the contact between hydrogen and active sites
Surface Coating	Promote the adsorption and desorption of hydrogen gas
Optimize the preparation process	Improve melting and casting methods to achieve a more ideal organizational structure
Using advanced preparation techniques	Mechanical alloying to improve the uniformity and activity of alloys Constructing composite materials using carbon materials to enhance hydrogen storage performance
Pretreatment	Hydrogenation pretreatment of alloys to improve their subsequent hydrogen storage performance

Hydrogen absorption and desorption kinetics

The hydrogen absorption and desorption kinetics of TiFe alloy is very important. Hydrogen molecules are first dissociated and adsorbed on the surface of the alloy, and then diffused to the internal lattice Spaces and active sites of the alloy. The hydrogen absorption rate is mainly limited by the hydrogen diffusion rate. The initial adsorption is fast, but the diffusion rate decreases with the increase of hydrogen content. Diffusion is affected by temperature, pressure and microstructure. Higher temperature generally accelerates the diffusion of hydrogen atoms, while increasing the pressure of hydrogen provides a stronger driving force to push more hydrogen atoms into the alloy.⁸² The high efficiency hydrogen absorption and desorption kinetics of TiFe alloy can greatly enhance its hydrogen storage application value. However, the hydrogen absorption and desorption kinetics of the alloy is often limited by factors such as impurities, crystal defects, grain size, and surface oxidation. Therefore, it is necessary to optimize the composition of TiFe alloy, improve the preparation process and surface treatment. The pressure-composition-temperature (P–C–T) curves of TiFe alloys at different temperatures are shown in Figure 8. As can be seen in Figure 8(a), the curves have two plateaus when the temperature is below 55 °C.From P–C–T curves of TiFe-H system at 40°C in Figure 8(b), it can be seen that the hysteresis is obvious because of the large equilibrium pressure difference of hydrogen absorption and desorption, 2 hysteresis loops are formed in the hydrogen absorption. The P-C-T curve in the hydrogen absorption and discharge process can provide thermodynamic information of the alloy and help to analyze the thermodynamic driving force of hydrogen absorption and discharge.

Figure 8.

P-C-T curves for TiFe-H system at different temperatures (a) and 40 °C (b).

In order to improve the hydrogen absorption and desorption kinetics of TiFe alloy, many ways can be adopted. The alloying of nickel, manganese and other elements can adjust the crystal and electronic structure of TiFe alloy, optimize the diffusion path and adsorption position of hydrogen atoms, and thus accelerate the absorption and release of hydrogen.⁸³ Patel et al.⁸⁴ discovered that the combination of zirconium (Zr) and manganese (Mn) additions to the titanium-iron (TiFe) alloy demonstrates significantly enhanced hydrogen storage properties compared to the individual addition of either Zr or Mn alone. Specifically, the TiFe alloy with 2 wt% Mn and 4 wt% Zr initially absorbed 2 wt% of hydrogen at room temperature under a pressure of 2 MPa, whereas the TiFe alloy with only 4 wt% Zr absorbed merely 1.2 wt% of hydrogen under identical conditions. Guéguen et al.⁸⁵ reported that the incorporation of vanadium (V) into TiFe0.8Mn0.1 significantly reduced hydrogen sorption hysteresis and flattened the hydrogen sorption plateaus. Furthermore, the alloy exhibited excellent activation properties at room temperature.

In order to achieve the reversible hydrogen storage capacity of 1.81% within 15 min, Li et al.⁸⁶ is close to the theoretical hydrogen storage capacity of 1.86% of TiFe alloy. The effect of Pr content on hydrogen storage properties of Ti_1.1−xPr_xFe_0.8Mn_0.2 (x = 0, 0.02, 0.04, 0.06, 0.08) alloy was also studied. It is pointed out that when Pr content is greater than or equal to 0.04, the alloy can be activated directly without incubation period. After the incorporation of Pr, the surface energy of the crystal surface of TiFe (111) is smaller, and hydrogen atoms are more easily diffused from the surface to the interior. In addition, the addition of Pr also refines the grains, introduces a large number of grain boundaries and defects, and improves the activation rate and kinetic properties, as shown in Figure 9. The physical adsorption results show that the specific surface area of ferrotitanium alloy after hydrogen absorption increases significantly after Pr doping.

Figure 9.

Activation curves of Ti_1.1−xPr_xFe_0.8Mn_0.2 alloy.

Adjusting the microstructure of materials, such as refining grains, can increase the number of grain boundaries, provide more paths for the diffusion of hydrogen atoms, and accelerate the process of hydrogen absorption and release.⁸⁷ Vega and co-workers⁸⁸ prepared TiFe -based alloys by high-energy ball milling for 2, 6 and 10 h. The hydrogen storage capacity of the samples for 2, 6 and 10 h reached about 0.9%, 1% and 1.09%, respectively. After grinding, the sample needs to be thermally-activated (or reactivated) to provide conditions for the first hydrogen absorption. At the same time, with the extension of milling time, the absorption kinetics of the sample is faster and faster. By SEM and Transmission Electron Microscope (TEM), it was found that the average grain size and microcrystal size of the alloy decreased to 7 nm and 11 nm, respectively. Therefore, ball milling makes sample activation easier and the hydrogen pressure for activation smaller by changing the grain size of TiFe.

Emami and co-workers⁸⁹ reported that the 36 h-milled TiFe alloys can absorb hydrogen up to 1.5 wt% of hydrogen at 303 K. They further claimed that ball-milled TiFe powder is not deactivated after being kept under air for 1 month, which would be a remarkable result if true. The TEM tests revealed that the ball-milling processing of TiFe results in the formation of nanograins, with minimal generation of cracks or dislocations. The nanograin boundaries were postulated to act as pathways for the transportation of hydrogen atoms through the oxide layer in ball-milled TiFe, with the oxygen molecules unable to penetrate these ultrafine pathways.

The majority of ultrafine-grained and nanostructured alloys exhibit a high density of lattice defects as a result of severe plastic deformation (SPD) techniques.⁹⁰ It is thought that SPD induced by high-pressure torsion (HPT) represents a viable method for activating passivated TiFe alloys.^91,92 In a seminal contribution, Edalati et al.⁹³ introduced the use of HPT for the activation of TiFe alloys. The microstructure of the HPT-processed TiFe is heterogeneous, comprising nanograins, coarse grains, amorphous-like phases, and disordered phases. Additionally, the material exhibits the capacity to absorb 1.7 wt.% of hydrogen at room temperature.

In addition, surface alloying mainly uses physical and chemical methods to deposit an alloy layer on the metal surface to improve the performance of hydrogen storage alloys, which can also effectively promote the adsorption and desorption of hydrogen and improve the kinetic performance. As early as 1993,⁹⁴ Lue et al. modified the surface of TiFe alloy by adding a small amount of LaNi₅, which was used for short-term ball milling, and could enable the TiFe alloy to absorb hydrogen at a hydrogen pressure of 4 MPa and room temperature, and improve the activation performance and resistance to oxygen poisoning.

The hydrogen absorption and release kinetics of TiFe alloy is centered. Compared with the LaNi₅, TiFe exhibits slower hydrogen uptake at room temperature, and the LaNi₅ has a faster hydrogen diffusion rate and more favorable hydrogen adsorption/desorption thermodynamic characteristics. However, compared with some complex chemical hydrogen storage materials such as sodium borohydride, TiFe has a simple hydrogen absorption and release process and good cycling. TiFe has more potential for comprehensive performance in specific scenarios.

TiFe alloys have been considered for automobiles. Several hydrogen-powered vehicles have been built using TiFe alloys as fuel storage media.⁹⁵ TiFe alloys can also be employed as thermal energy storage materials.⁹⁶ The Australian company Electromagnetic Compatibility Solar has developed a concept for a concentrated solar tower plant that incorporates a CaH₂ heat storage system and a Stirling engine, delivering a continuous output of 100 kWel. During the energy storage process, the hydrogen released is stored in the form of TiFe hydride. At the beginning of the twenty-first century, due to the versatility of hydride energy storage systems for wind power generation,⁹⁷ applications of TiFe-based hydrogen storage alloys in the field of solar and wind energy have been proposed to collect the energy generated by solar and wind energy, generate hydrogen by electrolysis of water and store it in TiFe-based hydrogen storage alloys to achieve energy recycling with high application value.⁹⁸ However, the demand for high hydrogen absorption and discharge rate needs to be optimized or better materials should be considered. In practical applications, the selection of hydrogen storage materials requires comprehensive consideration of hydrogen storage capacity, hydrogen absorption and desorption kinetics, cost, safety and other factors.

Challenges and prospects

The commercialization of TiFe solid-state hydrogen storage alloys faces three major challenges, including cycle stability, activation conditions and cost reduction (Table 5).

Cycle stability. The hydrogen storage performance of TiFe alloy may be attenuated after several cycles of hydrogen absorption and discharge, which will affect its long-term application reliability. In order to improve the cycle stability of TiFe alloy, researchers are focusing on the optimization of alloy composition, the improvement of preparation technology, and the addition of efficient catalysts to enhance the performance stability of TiFe alloy in the process of repeated hydrogen absorption and discharge.

Activation conditions. The harsh activation conditions of TiFe alloy limit its application potential and affect its applicability in specific scenarios. The “First Hydrogenation” is a crucial step in the activation process. Through alloying treatment, nanostructure regulation and other technical paths, researchers are trying to reduce the activation conditions of TiFe alloy, in order to broaden its application field and improve its environmental adaptability.

Cost reduction. To realize large scale commercialization of TiFe solid state hydrogen storage alloy materials, production costs must be cut. This is crucial for their broad application. Current research focuses on reducing costs through optimizing raw material procurement, streamlining production processes, and boosting large scale production efficiency. Energy efficient methods like the Hydride Cycle and combustion techniques (SHS, self-ignition combustion synthesis (SICS)) are particularly promising. The Hydride Cycle leverages the reversible hydrogen absorption/desorption of TiFe, lowering energy consumption during production. SHS and SICS initiate reactions via initial energy input, generating heat to sustain the process, thus saving energy. By applying these strategies, it's expected to greatly reduce the preparation cost of TiFe alloy materials. This will speed up their adoption in the hydrogen economy, promoting sustainable energy solutions and advancing the hydrogen energy based economy.

Table 5.

Key challenges and solutions for commercial applications.

Challenge areas	Description of the problem	Research progress and solutions
Cyclic stability	Hydrogen storage performance may diminish during cycling	Optimization of alloy compositions, improvement of preparation techniques, addition of catalysts to improve cycling stability
Activation condition	Harsh activation conditions limit application potential	Reduced activation conditions and improved environmental adaptability through alloy treatment, nanostructure modulation
Cost reduction	High production costs hinder large-scale commercialization	Optimizing raw material procurement, streamlining production processes, and improving production efficiency to reduce costs

As for solid hydrogen storage materials, TiFe based hydride materials have been the main focus of hydrogen storage alloys due to the richness of raw materials, excellent reversibility and low cost. The current research trend of TiFe hydrogen storage alloy is mainly to improve its activation properties, kinetics, thermodynamic stability and cycle life by changing the matrix structure and innovating the process route. As a potential material for the hydrogen energy economy, TiFe has shown remarkable development prospects.

Looking forward to the future, with the continuous progress of material science and engineering technology, the hydrogen storage performance of TiFe alloy is expected to achieve a qualitative leap. The activation properties of TiFe alloys can be significantly improved through more accurate adjustment of alloy composition, combined with advanced preparation processes such as mechanical alloying, plasma spraying, electrochemical deposition, etc., so that it can quickly react with hydrogen under mild conditions. By optimizing the microstructure and surface properties of TiFe alloy, the kinetic properties of hydrogen absorption and desorption can be significantly improved to meet the urgent demand of modern energy systems for rapid hydrogen charging and desorption. This not only enhances the utility of TiFe alloys, but also provides the possibility to build efficient and flexible hydrogen energy infrastructure. With the breakthrough of a series of key technologies, TiFe alloy will gradually show a more mature and extensive application prospect, laying a solid foundation for the realization of a clean, safe and sustainable hydrogen energy economic system.

Footnotes

Acknowledgements

This work is financially supported by NSFC (No. 22478206), basic scientific research project of Liupanshan Laboratory (No. LPS-2025-KY-D-JC-0019) and Ningxia University Graduate Student Innovation Program(CXXM2025109).

Author contribution

Tao Zhang: Writing – original draft, Writing – review & editing; Wenying Ma: Writing – original draft; Ying Li: Writing – review & editing Haowei Liu: Writing – review & editing; Jiaqi Chen: Project administration, Funding acquisition; Yonghong Li: Project administration, Funding acquisition; Xiaoxia Jiang Project administration, Supervision; Hongcun Bai: Project administration, Resources, Funding acquisition.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

References

Yusaf

Mahamude

ASF

Kadirgama

, et al. Sustainable hydrogen energy in aviation–A narrative review. Int J Hydrogen Energy 2024; 52: 1026–1045.

Evro

Oni

Tomomewo

. Carbon neutrality and hydrogen energy systems. Int J Hydrogen Energy 2024; 78: 1449–1467.

Hirscher

Yartys

Baricco

, et al. Materials for hydrogen-based energy storage past, recent progress and future outlook. J Alloys Compd 2020; 827: 153548.

Osman

Mehta

Elgarahy

, et al. Hydrogen production, storage, utilisation and environmental impacts: a review. Environ Chem Lett 2022; 20: 153–188.

Agaton

Batac

KIT

Reyes

Jr . Prospects and challenges for green hydrogen production and utilization in the Philippines. Int J Hydrogen Energy 2022; 47: 17859–17870.

El-Shafie

. Hydrogen production by water electrolysis technologies: a review. Results in Engineering 2023; 20: 101426.

Wei

Tukker

Suh

. Future environmental impacts of global hydrogen production. Energy and Environmental Science 2024; 17: 2157.

Abbas

Hassan

Tabar

, et al. Techno-economic analysis for clean hydrogen production using solar energy under varied climate conditions. Int J Hydrogen Energy 2023; 48: 2929–2948.

Weidner

Tulus

Guillén-Gosálbez

. Environmental sustainability assessment of large-scale hydrogen production using prospective life cycle analysis. Environ Chem Lett 2023; 48: 8310–8327.

10.

Oliveira

Beswick

Yan

. A green hydrogen economy for a renewable energy society. Curr Opin Chem Eng 2021; 33: 100701.

11.

Niaz

Manzoor

Pandith

. Hydrogen storage: materials, methods and perspectives. Renewable Sustainable Energy Rev 2015; 50: 457–469.

12.

E L Abdechafik

H A

Ousaleh

Mehmood

Y F

. An analytical review of recent advancements on solid-state hydrogen storage. International Journal of Hydrogen Energy 2024; 52: 1182–1193.

13.

Dematteis

E M

Berti

Cuevas

, M, et al. Substitutional effects in TiFe for hydrogen storage: a comprehensive review. Mater Adv 2021; 2: 2524–2560.

14.

Ren

Musyoka

Langmi

, et al. Current research trends and perspectives on materials-based hydrogen storage solutions: a critical review. Int J Hydrogen Energy 2017; 42: 289–311.

15.

Jiang

. Expediting the innovation and application of solid hydrogen storage technology. Engineering 2021; 7: 731–733.

16.

Park

, et al. Investigation on the changes of pressure and temperature in high pressure filling of hydrogen storage tank. Case Stud Thermal Eng 2022; 37: 102143.

17.

I A Hassan

S Ramadan

M A

Saleh

. Hydrogen storage technologies for stationary and mobile appli-cations: Review, analysis and perspectives. Renewable and Sustainable Energy Reviews 2021; 149(111311).

18.

Samantaray

Putnam

Stadie

. Volumetrics of hydrogen storage by physical adsorption. Inorganics 2021; 9: 45.

19.

Sazali

. Emerging technologies by hydrogen: a review. Int J Hydrogen Energy 2020; 45: 18753–18771.

20.

Wang

Y Q

Wang

S S

, etal. Hydrogen storage in branch mini-channel metal hydride reactor: Optimization design, sensitivity analysis and quadratic regression. International Journal of Hy-drogen Energy 2021(49): 25189–25207.

21.

Lan

Wei

, et al. Improvement of hydrogen absorption and desorption properties of TiFe-based alloys by adding yttrium. J Alloys Compd 2022; 927: 166992.

22.

Endo

Goshome

Tetsuhiko

, et al. Thermal management and power saving operations for improved energy efficiency within a renewable hydrogen energy system utilizing metal hydride hydrogen storage. Int J Hydrogen Energy 2021; 46: 262–271.

23.

Yang

Deng

Wang

, et al. High pressure hydrogen leakage diffusion: research progress. Int J Hydrogen Energy 2024; 50: 1029–1046.

24.

Zhang

, et al. Research and application of Ti–Mn-based hydrogen storage alloys. J Iron Steel Res Int 2023; 30: 611–625.

25.

Kubas

. Chemical bonding of hydrogen molecules to transition metal complexes. J Less Common Metals 1991; 172–174: 475–484.

26.

Kubas

. Fundamentals of H2 binding and reactivity on transition metals underlying hydrogenase function and H2 production and storage. Chem Rev 2007; 107: 4152–4205.

27.

Akiyama

Isogai

Yagi

. Hydriding combustion synthesis for the production of hydrogen storage alloy. J Alloys Compd 1997; 252: L1–L4.

28.

Sujan

Pan

, et al. An overview on TiFe intermetallic for solid-state hydrogen storage: microstructure, hydrogenation and fabrication processes. Crit Rev Solid State Mater Sci 2019; 45: 410–427.

29.

Zhang

Yuan

, et al. Research progress of TiFe-based hydrogen storage alloys. J Iron Steel Res Int 2022; 29: 537–551.

30.

Han

Zhai

, et al. Effect on the activation and hydrogen storage properties of Y–TiFe-based composites with vanadium via mechanical milling. Int J Hydrogen Energy 2025; 106: 686–699.

31.

Endo

Goshome

Tetsuhiko

, et al. Thermal management and power saving operations for improved energy effciency within a renewable hydrogen energy system utilizing metal hydride hydrogen storage. Int J Hydrogen Energy 2021; 46: 262–271.

32.

Dematteis

Cuevas

Latroche

. Hydrogen storage properties of Mn and Cu for Fe substitution in TiFe_0.9 intermetallic compound. J Alloys Compd 2021; 851: 156075.

33.

Zhang

Yuan

, et al. Research progress of TiFe-based hydrogen storage alloys. J Iron Steel Res Int 2022; 29: 537–555.

34.

Zhang

Guo

, et al. Application research on TiFe-based hydrogen storage alloys in field of vehicle energy storage. Chin J Rare Metals 2017; 41: 515.

35.

Benyelloul

Bouhadda

Bououdina

, et al. The effect of hydrogen on the mechanical properties of FeTi for hydrogen storage applications. Int J Hydrogen Energy 2014; 39: 12667–12675.

36.

Polanski

Kwiatkowska

Kunce

, et al. Combinatorial synthesis of alloy libraries with a progressive composition gradient using laser engineered net shaping (LENS): hydrogen storage alloys. Int J Hydrogen Energy 2013; 38: 12159–12171.

37.

Laves

Wallbaum

. Zur Kristallchemie von Titan-Legierungen. Naturwissenschaften 1939; 27: 674–675.

38.

Thompson

Reilly

Reidinger

, et al. Neutron diffraction study of gamma iron titanium deuteride. J Phy F Metal Phy 1979; 4: L61–L66.

39.

Melnyk

Tremel

. The titanium–iron–antimony ternary system and the crystal and electronic structure of the interstitial compound Ti5FeSb2. J Alloys Compd 2003; 349: 164–171.

40.

Inoue

Kotani

Chiku

, et al. Ti-V-Cr-Ni alloys as high capacity negative electrode active materials for use in nickel-metal hydride batteries. Int J Hydrogen Energy 2016; 41: 9939–9947.

41.

Thompson

Reidinger

Reilly

, et al. Neutron diffraction study of α-iron titanium deuteride. J Phys F Met Phys 1980; 10: L57–L59.

42.

Nong

Zhu

Yang

, et al. First-principles study of hydrogen storage and diffusion in B2 FeTi alloy. Comput Mater Sci 2014; 81: 517–523.

43.

Liu

Zhang

Sun

, et al. An overview of TiFe alloys for hydrogen storage: structure, processes, properties, and applications. J Energy Storage 2023; 68: 107772.

44.

Kraan

AMV

Buschow

KHJ

. The 57Fe Mssbauer isomer shift in intermetallic compound of iron. Physica 1986; 138: 55–62.

45.

, etal. Corrosion Resistance of Ti-Fe Binary Alloys Fabricated by Powder Metallurgy. Acta Metall Sin 2017; 53(1): 38–46.

46.

Louzguine

Kato

Louzguina

, et al. High-strength binary Ti-Fe bulk alloys with enhanced ductility. J Mater Res 2004; 19: 3600–3606.

47.

Archi

Bajjou

Rahmani

, et al. A comparative ab initio analysis of the stability, electronic, thermodynamic, mechanical, and hydrogen storage properties of SrZnH3 and SrLiH3 perovskite hydrides through DFT and AIMD approaches. Int J Hydrogen Energy 2025; 105: 759–770.

48.

Shang

Liu

Liang

, et al. Developing sustainable FeTi alloys for hydrogen storage by recycling. Commun Mater 2022; 3: 101.

49.

Davids

Martin

Fursikov

, et al. Effect of preparation routes on the performance of a multi-component AB2-type hydrogen storage alloy. J Phy: Energy 2024; 6: 035005.

50.

Fashu

Lototskyy

Davids

, et al. A review on crucibles for induction melting of titanium alloys. Mater Des 2022; 186: 108295.

51.

Shang

Zhang

, et al. Effect of Pr content on activation capability and hydrogen storage performances of TiFe alloy. J Alloys Compd 2022; 890: 161785.

52.

Liu

Dixit

. Improved hydrogen storage properties of TiFe alloy by doping (Zr+2 V) additive and using mechanical deformation. Int J Hydrogen Energy 2019; 44: 27843–27852.

53.

Liu

Zhang

J X

Zhou

C S

, etal. Hydrogen Storage Properties of Ti-Fe-Zr-Mn-Nb Alloys. Journal of Alloys and Compounds 2023; 938: 168466.

54.

Dematteis

Dreistadt

Capurso

, et al. Fundamental hydrogen storage properties of TiFe-alloy with partial substitution of Fe by Ti and Mn. J Alloys Compd 2021; 874: 159925.

55.

Barale

Dematteis

Capurso

, et al. Tife0.85Mn0.05 alloy produced at industrial level for a hydrogen storage plant. Int J Hydrogen Energy 2022; 47: 29866–29880.

56.

Suryanarayana

. Mechanical alloying and milling. Prog Mater Sci 2001; 46: 1–184.

57.

Liu

Cai

, et al. Hydrogen storage behaviour of Cr- and Mn-doped Mg2Ni alloys fabricated via high-energy ball milling. Int J Hydrogen Energy 2023; 48: 17202–17215.

58.

Falcão

Dammann

EDCC

Rocha

, et al. Synthesis of TiFe compound from ball milled TiH₂ and Fe powders mixtures. Mater Sci Forum 2014; 802: 61–65.

59.

Yang

Sun

Fang

, et al. Effect of ball milling nanocrystallization on hydrogen storage performance of Mg₉₅Ni₂Pr₃ hydrogen storage alloy. Mater Today Commun 2024; 40: 109380.

60.

Falcão

Dammann

EDCC

Rocha

, et al. An investigation on the mechanical alloying of TiFe compound by high-energy ball milling. Mater Sci Forum 2010; 660–661: 329–334.

61.

Vega

LER

R Leiva

Neto

RML

, et al. Improved ball milling method for the synthesis of nanocrystalline TiFe compound ready to absorb hydrogen. Int J Hydrogen Energy 2020; 45: 2084–2093.

62.

Dolukhanyan

Sh Shekhtman

Aleksanyan

, et al. Features of the formation of alloys and their hydrides in the Ti-Zr-H system. Khim Fiz 2007; 26: 336–343.

63.

Dolukhanyan

Hakobyan

Aleksanyan

, et al. Combustion of metals in hydrogen and hydride production by self-propagating high-temperature synthesis. Int J Self Propag High Temp Synth 1992; 1: 530–535.

64.

Mayilyan

Aleksanyan

. Tife hydrogen storage alloys produced by “hydride cycle” method. Russ J Phys Chem A 2023; 97: 3143–3148.

65.

Aleksanyan

Dolukhanyan

Ter-Galstyan

, et al. Formation Ti₆Al₄V alloy by hydride cycle mode and its (Ti₆Al₄V)H_1.606 hydride in self-propagating high-temperature synthesis mode. Int J Hydrogen Energy 2021; 46: 15738–15747.

66.

Aleksanyan

Dolukhanyan

Ter-Galstyan

, et al. Hydride cycle formation of ternary alloys in TiVMn system and their interaction with hydrogen. Int J Hydrogen Energy 2016; 41: 13521–13530.

67.

Reilly

Wiswall

. Formation and properties of iron titanium hydride. Inorg Chem 1974; 13: 218–222.

68.

Guzik

Sartori

, et al. Effect of ball milling and cryomilling on the microstructure and first hydrogenation properties of TiFe+4 wt.% Zr alloy. J Mater Res Technol 2019; 8: 1828–1834.

69.

Patel

Duguay

Tougas

, et al. Study of the microstructural and first hydrogenation properties of TiFe alloy with Zr, Mn and V as additives. Processes 2021; 9: 1217.

70.

Razafindramanana

Gorsse

Huot

, et al. Effect of hafnium addition on the hydrogenation process of TiFe alloy. Energies 2019; 12: 3477.

71.

Gosselin

Huot

. First hydrogenation enhancement in TiFe alloys for hydrogen storage doped with yttrium. Metals (Basel) 2019; 9: 242.

72.

Reilly

. Metal hydrides as hydrogen storage media and their applications. Upton, NY, USA: Brookhaven National Lab, 1976.

73.

Zhao

Han

, et al. Optimizing microstructure and enhancing mechanical properties of Al–Si–Mg–Mn-based alloy by novel C-doped TiB2 particles. J Mater Res Technol 2023; 26: 9450–9466.

74.

Edalati

Matsuda

Arita

, et al. Mechanism of activation of TiFe intermetallics for hydrogen storage by severe plastic deformation using highpressure torsion. Appl Phys Lett 2013; 103: 143902.

75.

Sheng

Sun

, et al. Hydrogen storage thermodynamics and kinetics of the as-cast and milled Ce-Mg-Ni-based alloy. Materials Today Communications 2023; 35: 106217.

76.

Zhang

Shang

, et al. Hydrogen storage characteristics of Ti1.04Fe0.7Ni0.1Zr0.1Mn0.1Pr0.06 alloy treated by ball milling. J Alloys Compd 2023; 930: 167024.

77.

Guo

Kisaki

Jain

, et al. Degradation and recovery properties in thermochemical hydrogen compression by using TiFe alloy. Int J Hydrogen Energy 2023; 48: 35164–35169.

78.

O'Flynn

Corbin

. The influence of iron powder size on pore formation. densification and homogenization during blended elemental sintering of Ti_2.5Fe. J Alloys Compd 2015; 618: 437–448.

79.

Tian

Wang

, et al. Microstructure characteristics and hydrogen storage kinetics of Mg77 + xNi20−xLa3 (x = 0, 5, 10, 15) alloys. Materials (Basel) 2023; 16: 4576.

80.

Zeng

Wang

, et al. Influence of Zr addition on the microstructure and hydrogenation kinetics of Ti50−xV25Cr25Zrx (x = 0, 5, 7, and 9) alloys. Materials (Basel) 2024; 17: 1366.

81.

Kumar

Xiong

H Wan

, et al. Ball milling as a mechanochemical technology for fabrication of novel biochar nanomaterials. Bioresour Technol 2020; 312: 123613.

82.

Luo

, et al. Thermodynamics and kinetics of hydriding and dehydriding reactions in Mg-based hydrogen storage materials. J Magnesium Alloys 2021; 9: 1922–1941.

83.

Zhu

Yang

, et al. Compositionally complex doping for low-V Ti-Cr-V hydrogen storage alloys. Chem Eng J 2023; 477: 146970.

84.

Patel

Duguay

Tougas

, et al. Microstructure and first hydrogenation properties of TiFe alloy with Zr and Mn as additives. Int J Hydrogen Energy 2020; 45: 787–797.

85.

Guéguen

Latroche

. Influence of the addition of vanadium on the hydrogenation properties of the compounds TiFe0.9Vx and TiFe0.8Mn0.1Vx (x=0, 0.05 and 0.1). J Alloys Compd 2011; 509: 5562–5566.

86.

Liu

Wei

, et al. A significantly improved hydrogen storage performance of nanocrystalline Ti-Fe-Mn-Pr alloy. J Mater Res Technol 2023; 23: 4566–4575.

87.

Liu

Zhang

Sun

, et al. Effect of oxygen on the hydrogen storage properties of TiFe alloys. J Energy Storage 2022; 55: 105543.

88.

Vega

LER

R Leiva

Neto

RML

, et al. Improved ball milling method for the synthesis of nanocrystalline TiFe compound ready to absorb hydrogen-science direct. Int J Hydrogen Energy 2020; 45: 2084.

89.

Emami

Edalati

Matsuda

, et al. Hydrogen storage performance of TiFe after processing by ball milling. Acta Mater 2015; 88: 190–195.

90.

Edalati

Bachmaier

Beloshenko

, et al. Nanomaterials by severe plastic deformation: review of historical developments and recent advances. Mater Res Lett 2022; 10: 163–256.

91.

Edalati

Akiba

Horita

. High-pressure torsion for new hydrogen storage materials. Sci Technol Adv Mater 2018; 19: 185–193.

92.

Révész

Gajdics

. High-pressure torsion of non-equilibrium hydrogen storage materials: a review. Energies 2021; 14: 819.

93.

Edalati

Matsuda

Iwaoka

, et al. High-pressure torsion of TiFe intermetallics for activation of hydrogen storage at room temperature with heterogeneous nanostructure. Int J Hydrogen Energy 2013; 38: 4622–4627.

94.

Lü

Zhang

Wang

, et al. Surface modification of powder materials and room temperature activation of V, Ni and TiFe. Scr Metall Mater 1993; 29: 1253–1258.

95.

Xie

Jin

, et al. A review of hydrogen storage and transportation: progresses and challenges. Energies 2024; 17: 4070.

96.

Sheppard

Paskevicius

Humphries

, et al. Metal hydrides for concentrating solar thermal power energy storage. Appl Phys A 2016; 122: 395.

97.

Xiao

, et al. Optimal operation of a wind-electrolytic hydrogen storage system in the electricity/hydrogen markets. Int J Hydrogen Energy 2020; 45: 24412–24423.

98.

Nivedhitha

Beena

Banapurmath

, et al. Advances in hydrogen storage with metal hydrides: mechanisms, materials, and challenges. Int J Hydrogen Energy 2024; 61: 1259–1273.