This work presents an integrated solid-state hydrogen compression and storage system coupled with PEMFC stacks. La0.9Ce0.1Ni5 (LCN-C) with low equilibrium pressure (Peq) is used as hydrogen compression, and La0.6Ce0.4Ni5 (LCN-S) with higher Peq is as hydrogen storage. The system involves two compression modules and four storage modules with the LCN-C:LCN-S weight ratio of 1.33:1. LCN-C compresses hydrogen from ∼6 bar to 20–33 bar, subsequently stored in LCN-S. Upon 100 hydrogen compression and storage cycles, the system reversibly delivers up to 0.94 ± 0.12 wt% H2. Compatible equilibrium pressures of both hydrides and optimized de/rehydrogenation kinetics through suitable hydride weight ratio influence hydrogen compression and storage efficiency. Electrical power generation of the integrated system coupled with PEMFC stacks is investigated. A constant flow of up to 6.5 L H2/min is supplied to three parallel PEMFC stacks for 200 min, producing 1.73 kWh. Up to 89.4 % of total hydrogen capacity is utilized during electricity generation.

The influence of ordered mesoporous carbon (CMK-3) on the hydrogen storage properties of the 6Mg(NH2)2-9LiH-2LiBH4 reactive hydride composite (6 : 9 : 2-RHC) is systematically investigated. Incorporation of 10 wt% CMK-3 into the pristine composite (6 : 9 : 2-RHC + 0.1CMK3) leads to substantial improvements in hydrogen sorption kinetics. Under identical thermodynamic conditions, the CMK-3 incorporated composite exhibits significantly enhanced reaction kinetics, with the absorption time reduced from similar to 30 minutes to only 3 minutes (approximate to 90% improvement) and the full desorption completed within 25 minutes instead of 60 minutes (approximate to 58% improvement) compared to the pristine system. Moreover, the modified composite maintains excellent cycling stability, with 98% capacity retention over the first ten dehydrogenation/hydrogenation cycles compared to 90% for the pure composite. To elucidate the mechanism underlying this kinetic enhancement, we use a combination of advanced characterization techniques, including differential thermal analysis (DTA), synchrotron radiation X-ray powder diffraction (SR-XRPD), Fourier transform infrared (FT-IR) spectroscopy, small-angle and ultra-small-angle neutron scattering (SANS/USANS) and quasi-elastic neutron scattering (QENS). DTA analysis shows an 11 kJ mol-1 decrease in apparent activation energy barrier upon CMK-3 addition. SANS/USANS results reveal that CMK-3 effectively suppresses particle agglomeration during the dehydrogenation/hydrogenation cycle and maintains structural integrity, preserving the high accessible surface area for long-term cycling stability. QENS measurements confirm that the incorporation of mesoporous carbon lowers the reorientational energy barriers of [BH4]- anions, leading to faster local dynamics. This enhanced mobility facilitates the elementary reaction steps involved in hydrogen release and uptake, which contributes to the improved sorption kinetics of the CMK-3 modified composite.

Ilmenite, TiFeO 3 , is an earth-abundant mineral commonly used as a feedstock for TiO 2 , Ti, and Fe via reduction. One reduction product currently being explored is TiFe, an intermetallic compound capable of reversible, near-ambient hydrogen storage. Here, we use first-principles calculations coupled with CALPHAD thermodynamic modeling to evaluate how the kinetics and thermodynamics of point defects and impurities may hinder or facilitate this reduction process. We find that certain impurities within ilmenite can lower the thermodynamic barrier to reduction, including elements such as Mn and Si that are commonly found in the naturally occurring mineral. Elements like Cr, Mn, and V, which considerably decrease the reduction barrier, also offer benefits for the hydrogen storage properties of TiFe, making them valuable at both ends of the reaction. Based on thermodynamic analysis, we find Co and Mn to be particularly promising, because they are fully soluble for Fe in the ilmenite lattice and will not form secondary oxide phases. Additionally, we find that the choice of reduction agent (e.g., {Ca,Mg}H 2 , {Ca,Mg}Cl 2 , {Ca,Mg}F 2 , or {Ca,Mg} metal) affects the favorability of reduction. Native oxygen vacancies have high formation energies; however, the substitutional species H O and F O have much lower energies under H-rich and F-rich conditions, indicating that oxygen removal will be enhanced with H-or F-based reduction agents. Furthermore, diffusion pathways for V O and anion substitutional species are likely to be activated at elevated temperatures typical of reduction, meaning that they can move into and out of the ilmenite lattice readily. Our results provide valuable guidance for engineering ilmenite to facilitate its direct reduction to TiFe, while also offering general insights into how unintentional impurities in reduction flows may contribute to high-value product materials.

Complex hydrides offer high H2 storage capacities but suffer from kinetic degradation and microstructural coarsening, requiring operations at elevated temperatures, typically above 180°C. Here, we demonstrate grain boundary complexion-mediated structural stabilization using ultra-low loading of Zr-based metal-organic frameworks (Zr-MOFs; 1 at.% Zr; UiO-66 vs. MIP-206) in the reactive hydride composite system 6Mg(NH2)2-9LiH-2LiBH4 (6.9.2-RHC). Incorporation of microporous Zr-UiO-66 significantly lowers the hydrogen absorption onset temperature from 162°C to 81°C, enables measurable hydrogen uptake at 35°C (1.07 wt.% under 80 bar H2). In addition, UiO-66 accelerates desorption by more than threefold at 140°C, increases reversible capacity from 3.2 to 4.1 wt.%, and maintains the capacity over 15 cycles compared with the pristine 6.9.2-RHC. In situ synchrotron radiation X-ray diffraction confirms that the intrinsic amide–imide reaction pathway remains unchanged, suggesting that structural stabilization plays a dominant role in the enhanced hydrogen storage performance. SAXS reveals stabilized nanoscale domains (≈2.4–3.3 nm), while SANS/USANS demonstrates suppression of hierarchical aggregation relative to pristine 6.9.2-RHC. Ball-milling of UiO-66 preserves short-range tetrahedral structural units (≈0.76 nm) that are proposed to stabilize grain-boundary complexions capable of accommodating the large (20–30 per cent) volume changes associated with hydrogen cycling. The performance hierarchy (UiO-66 > MIP-206 > pristine) demonstrates that MOF-derived short-range structural motifs suppress coarsening by promoting grain-boundary complexions, enabling practical low-temperature hydride operation through stabilized reactive interfaces.

The inherently low thermal conductivity of metal hydrides significantly hinders heat transfer and, consequently, the kinetics of hydrogen absorption and desorption processes. To address this limitation, strategies such as adding high-thermal-conductivity materials have been explored to enhance the effective thermal conductivity of hydride beds. In this work, we investigate the effects of expanded natural graphite (ENG) addition on the thermal and kinetic performance of composite metal hydride materials. The used alloy is a commercially available AB2 intermetallic compound, Hydralloy®C5. Materials composed of this AB2 alloy, ethylene-vinyl acetate copolymer (EVA) used as binder, and ENG are investigated here. Experimental tests are conducted in conjunction with multi-scale finite element method (FEM) simulations to evaluate the effects of EVA on the hydrogen storage performance, hydride bed temperature development, and the effective thermal conductivity. Among the tested compositions, the mixture C5 + 10 wt% ENG + 2.5 wt% EVA exhibited the best balance of thermal behavior and storage properties, achieving a capacity close to that of the pristine AB2 (about 1.7 wt%, calculated on the basis of the active material), showing an improvement of the kinetics around 35–40% and reducing the peak temperature upon hydrogenation in the milligram scale by approximately 8 °C. The proposed model introduces several novel elements, including a modified approach for the evaluation of the effective thermal conductivity and a mathematical model for the porosity of metal hydride composite beds. Validated FEM simulations at different scales (mg, g, and hundreds of grams), incorporating an effective thermal-conductivity model modified for composite materials, provide valuable input for the development and design of hydride-based vessels containing pure and composite hydride-forming materials.

Ilmenite is an abundant raw material with a general composition of FeTiO3, mainly used as ore for TiO2 production, which, among other applications, is used to produce titanium metal. This paper focuses on the direct reduction of ilmenite to iron–titanium alloys via thermochemical or mechanochemical processes. These processes were carried out in the presence of reducing agents such as magnesium, calcium, and gaseous hydrogen, as well as the combination of magnesium or calcium in a hydrogen atmosphere. The mixture of ilmenite and the reducing agents was ball milled for 80 h at 350 rpm and analyzed via X-ray powder diffraction (XRPD). The influence of particle size, by necessity reduced during the milling process, on the reduction is investigated via thermal analysis [differential thermal analysis (DTA) and differential scanning calorimetry (DSC)]. Additionally, the thermochemical reduction path is investigated via in situ synchrotron radiation XRPD. In this study, the mechanochemical reduction with magnesium and the thermochemical reduction with calcium yielded the highest conversion yield of ilmenite into iron–titanium alloy, forming primarily TiFe2 and small amounts of TiFe. TiFe is a promising hydrogen storage material. All runs were deficient in Ti after the reduction, as calculated by XRPD Rietveld refinement, which suggests the formation of an additional amorphous Ti–rich phase.

Hydrogen-based direct reduction of metal oxides is a ubiquitous solid-gas redox process central to geophysics, sustainable metallurgy, redox energy cycles and catalysis. During this process, hydrogen removes lattice oxygen to form water, yet product water has long been regarded as a passive exhaust, and its nanoscale formation, trapping and removal remain poorly understood. Here, we directly observe redox-product water release from iron oxide during hydrogen-based direct reduction. Because water removal emerges from coupled structural, chemical and crystallographic evolution across multiple length-scales under realistic non-equilibrium reaction-conditions, we establish a correlative multiscale in-situ approach that links pore evolution, molecular water signatures, phase transformation and chemical-state evolution during hematite reduction. We uncover a mechanism in which oxygen removal induces closed nanopores spatially delocalized from reaction surfaces, causing transient trapping of water vapor. Water is released only when these pores coalesce into a percolating network connected to the surface, coinciding with and accelerating the onset of the hematite-to-magnetite transformation. These findings show that dynamically evolving pore topology governs mass transport and redox kinetics in solid-gas reactions, closing a critical mechanistic gap in product-water removal and providing nanoscale guidance for hydrogen-based metal extraction, reactor design, and sustainable redox energy technologies under practical conditions.

Metal hydrides remain an intriguing alternative to conventional gaseous and liquid hydrogen storage methods, offering high volumetric storage density and enhanced hydrogen storage safety at ambient conditions. In this regard, the intermetallic compound FeTi is one of the most promising storage materials. However, its widespread industrial application remains challenging due to the need for activation, slow initial kinetics, large hysteresis, and high material costs. In this study, we aim to overcome these limitations by devising an alternative synthesis pathway to prepare nanoporous and ultra-fine porous FeTi with controlled grain and ligament sizes, allowing us to study the obtained well-defined microstructures in detail. In particular, we observe the confinement of the FeTi phase by surface oxides, which can be correlated with the hydrogen sorption properties of the respective material. These experimental results are further supported by an analytical model allowing the calculation of the absorption pressure as a function of microstructure-dependent elastic stresses. Additionally, we show that such stresses also influence the absorption-desorption hysteresis. This study lays the groundwork for the controlled and systematic study of the processing-structure-properties relations in metal hydrides and FeTi in particular, thereby paving the way to cost-effective and efficient hydrogen storage solutions based on metal hydrides.

Hydrogen storage in metal hydrides holds great promise for advancing a low-carbon energy future. Yet, fine-tuning the thermodynamics of hydrogen absorption remains challenging with traditional microalloying approaches. Here, we report a strategy inspired by compositionally complex alloy design to introduce atomic disorder into the prototypical TiFe intermetallic system. By progressively substituting Fe with Co, Ni, Cu, and Mn in equal proportions, we synthesize a series of near-single-phase B2-structured compositionally complex intermetallics, that is, Ti-50(FeCo)(50), Ti-50(FeCoNi)(50), Ti-50(FeCoNiCu)(50), and Ti-50(FeCoNiCuMn)(50) (at.%). These materials exhibit hydrogen storage capacities (measured by pressure-composition isotherm, PCI) of 1.39, 1.42, 1.31, and 1.14 wt.% under 100 bar of H-2 at 50 degrees C, respectively. Notably, Ti-50(FeCo)(50) demonstrates rapid hydrogen uptake kinetics, achieving 90% of its full capacity within 77 s under 50 bar of hydrogen pressure at 50 degrees C. Hydrogen storage thermodynamic analyses reveal that increasing atomic disorder stabilizes the hydride phase, with thermodynamic stability following the order: Ti-50(FeCoNiCuMn)(50) > Ti-50(FeCoNi)(50) > Ti-50(FeCoNiCu)(50) > Ti-50(FeCo)(50). Our findings establish atomic disorder as a versatile thermodynamic tuning knob for intermetallic hydrides, offering a rational framework for the design of advanced hydrogen storage materials.

Ultrahigh-strength bulk alloys with martensitic structures are essential for heavy-duty applications and infrastructure. However, they often contain small-angle grain boundaries (SAGBs), which enhance ductility but weaken resistance to dislocation motion. This limitation restricts tensile strength to below 2.5 GPa, even when nanoprecipitates or hierarchical architectures are introduced. Here we overcome this limitation by developing a near-single-phase martensitic alloy with a tensile strength exceeding 3 GPa. In the model (Fe49Co40Mo11)99.6B0.3C0.1 (at.%) alloy, cold rolling followed by low-temperature annealing introduces a high density of dislocations and drives Mo, C and B atoms to cosegregate at the SAGBs, forming interface complexes. These complexes stabilize the SAGBs, reinforce barriers to dislocation motion and still permit dislocation transmission across boundaries. As a result, the alloy achieves a tensile yield strength of 3.05 GPa and a fracture elongation of 5.13%, setting a benchmark for ultrahigh-strength, ductile alloys. This simple, scalable process integrates seamlessly with existing manufacturing methods and opens a path to next-generation structural materials.

Co-reduction of multicomponent oxides with hydrogen offers a carbon-neutral approach toward sustainable alloy design. Herein, we use in situ high-energy X-ray diffraction technique to gain insights into multicomponent oxide reduction of two precursor variants: mechanically mixed powders and pre-sintered oxide mixtures, targeting an equiatomic CoFeMnNi alloy. We find distinct reduction pathways and microstructure evolution, depending on initial precursors. Mixed powders are reduced to body-centered-cubic, face-centered-cubic, and MnO phases via halite, spinel, and Mn3O4 intermediates, whereas the pre-sintered complex oxide directly transforms into a mixture of metallic and MnO phases. The post-reduction microstructures were also strongly governed by the precursor state: mixed oxides exhibit loosely packed and coarse morphology, whereas the pre-sintered ceramic material showcases two distinct morphologies, either relatively dense metal-rich regions or regions with metallic nanoparticles supported on nanoporous MnO, highlighting the significant role of initial precursors on the final microstructure. Hence, precursor design strategies may offer a single-step route to nanoporous alloys with potential applications in catalysis and energy technologies.

We present an integrated experimental–theoretical investigation of the combined effects of Ni and Cr substitution in TiFe(1−x−y)CrxNiy on phase stability, lattice properties, and hydrogen sorption behavior. Alloys with fixed total substitution (x + y = 0.2) were synthesized by arc melting and characterized by X‐ray diffraction, electron microscopy, and pressure–composition–‍temperature measurements, complemented by density functional theory and CALPHAD modeling. Both substituents expand the B2 TiFe lattice and markedly reduce the equilibrium plateau pressure of the monohydride phase, indicating enhanced hydride stability while largely preserving reversible hydrogen capacity. Structural analysis shows that Cr promotes the formation of a C14 Laves secondary phase, whereas Ni stabilizes the B2 matrix; their combined addition leads to composition‐dependent coexistence of B2 and C14 phases in agreement with calculated phase equilibria. Thermodynamic analysis indicates that increased hydride stability correlates with both lattice expansion and the intrinsic hydrogen affinity of the substituents. The integrated experimental and modeling approach provides a coherent interpretation linking composition, phase stability, and hydrogen thermodynamics. These results provide quantitative guidance for tailoring TiFe‐derived hydrides from recycled steel feedstocks, supporting circular‐economy strategies for large‐scale hydrogen storage technologies.

In metals and alloys, solute segregation at grain boundaries typically undermines cohesion and ductility. Here, we overturn this paradigm by showing that solvent Fe atoms can preferentially enrich low-angle grain boundaries (LAGBs) in a ferrous alloy, dramatically enhancing ductility. Cold rolling and aging generate coherent nanoprecipitates, a high dislocation density, and abundant LAGBs in an austenitic matrix, yielding an ultrahigh tensile yield strength of similar to 1.74 GPa. Moreover, the solvent Fe enrichment at LAGBs lowers local stacking fault energy and activates austenite-to-martensite transformation under load. This transformation-induced plasticity effect stabilizes plastic flow, enabling a uniform elongation of similar to 26.2 % despite the alloy's exceptional strength. Our findings challenge conventional views of segregation and offer a new design strategy for ultra-strong, highly ductile alloys.

Modeling the impact of alloying on the hydrogenation properties of intermetallic compounds is a vital yet challenging task for hydrogen storage materials design: not only do these processes occur under thermodynamic para-equilibrium conditions, but for bcc-derived compounds, the task is further complicated through varying composition-dependent ordering transitions. Here, we tackle these challenges by providing a multicomponent thermodynamic modeling framework for FeTi, a representative bcc-derived material class, which is one of the most relevant room-temperature interstitial metal hydrides. We aim specifically to describe para-equilibrium FeTi-based multicomponent hydrides while ensuring compatibility with previously evaluated metallic systems. DFT point-defect calculations provide a physics-informed foundation to identify substitutional site preferences. Not only does our approach give detailed guidance for the selection of model parameters to evaluate phase equilibria for a broad range of FeTi-based multicomponent systems with high fidelity, but it also can be easily adopted to other interstitial hydrogen storage compounds.

Co-reduction of multicomponent oxides with hydrogen provides a carbon-neutral approach toward sustainable alloy design. Herein, we investigate the hydrogen-based direct reduction, using in-situ high-energy X-ray diffraction of two precursor variants: mechanically mixed powders and pre-sintered oxide mixtures, targeting an equiatomic CoFeMnNi alloy. We find distinct reduction pathways and microstructure evolution depending on initial precursors. Mixed powders at 700 °C are reduced to body-centered-cubic, face-centered-cubic, and MnO phases via halite, spinel, and Mn3O4 intermediates, whereas the pre-sintered material directly transforms into a mixture of metallic and oxide phases. The post-reduction microstructures are also different: mixed oxides show loosely packed morphology, whereas pre-sintered material reveals metallic nanoparticles supported on nanoporous MnO. The formation of nanoporous metallic networks is strongly governed by the precursor state, highlighting the role of initial precursors on the final microstructure. This precursor design strategy offers a single-step route to nanoporous alloys with potential applications in catalysis and energy technologies.

In metal hydride beds (MHBs), reaction heat transfer often limits the dynamic performance. Heat transfer within the MHB usually involves solid and gas phases. To account for both, an effective thermal conductivity (ETC) is defined. Measuring and predicting the ETC of metal hydride beds is of primary importance when designing hydride-based systems for high dynamics. This review paper presents an integral overview of the experimental and modeling approaches to characterize the ETC in MHBs. The most relevant methods for measuring the ETC of metal hydride beds are described, and the results and scopes are shown. A comprehensive description of the models applied to calculate the ETC of the MHBs under different conditions is developed. Moreover, the effects of operation parameters such as P, T, and composition on the ETC of the presented models are analyzed. Finally, a summary and conclusions about experimental techniques, a historical overview with a classification of the ETC models, a discussion about the needed parameters, and a comparison between ETC experimental and calculated results are provided.

The EU Horizon2020 RISE project 778,307 "Hydrogen fuelled utility and their support systems utilising metal hydrides" (HYDRIDE4MOBILITY) worked on the commercialization of hydrogen powered forklifts using metal hydride (MH) based hydrogen stores. The project consortium joined forces of 9 academic and industrial partners from 4 countries. The work program included a) Development of the materials for hydrogen storage and compression; b) Theoretical modelling and optimisation of the materials performance and system integration; c) Advanced fibre reinforced composite cylinder systems for H-2 storage and compression; d) System validation. Materials development was focused on i) Zr/Ti-based Laves type high entropy alloys; ii) Mg-rich composite materials; iii) REMNiSn intermetallics; iv) Mg based materials for the hydrolysis process; v) Cost-efficient alloys. For the optimized AB(2 +/- x) alloys the Zr/Ti content was optimized at A = Zr78-88Ti12-22 while B=Ni10Mn5.83VFe. These alloys provided a) Low hysteresis of hydrogen absorption-desorption; b) Excellent kinetics of charge and discharge; c) Tailored thermodynamics; d) Long cycle life. Zr0.85Ti0.15TM2 alloy provided a reversible H storage and electrochemical capacity of 1.6 wt% H and 450 mAh/g. The tanks development targeted: i) High efficiency of heat and hydrogen exchange; ii) Reduction of the weight and increasing the working H-2 pressure; iii) Modelling, testing and optimizing the H-2 stores with fast performance. The system for power generation was validated at the Implats plant in a fuel cell powered forklift with on-board MH hydrogen storage and on-site H-2 refuelling. The outcome on the HYDRIDE4MOBILITY project (2017-2024) (http://hydride4mobility.fesb.unist.hr) was presented in 58 publications.

Intermetallic titanium aluminides are interesting for aerospace and automotive applications due to their superior high-temperature mechanical properties. In particular, γ-TiAl-based alloys containing 5–10 at.% Niobium (Nb) have attracted significant attention. Molecular dynamics (MD) simulations can elucidate and optimize these materials, provided that accurate interatomic potentials are available. In this work, we compare active and passive machine learning approaches for developing TiAlNb interatomic potentials using both deep potential molecular dynamics (DeePMD) and the moment tensor potential (MTP) methods. Our comprehensive evaluation encompasses elastic constants, equilibrium volume, lattice parameters, and finite-temperature behavior, as well as simulated tension tests and generalized stacking fault energy calculations to assess the impact of Nb on the thermo-mechanical properties of γ-TiAl and α2-Ti3Al phases. Active learning consistently outperformed passive learning for both methods while requiring only a fraction of the training samples. Notably, active learning with DeePMD yielded a single potential capable of predicting the properties of both phases, whereas MTP exhibited limitations that necessitated separate training for each phase. Although active learning potentials excelled in predicting high-temperature behavior, their room-temperature property predictions were less accurate due to a sample selection bias toward higher temperatures. Overall, our thermomechanical analysis demonstrates that Nb incorporation enhances ductility while simultaneously reducing strength.

The transition to a hydrogen-based economy necessitates the development of safe, cost-effective hydrogen storage media at an industrial scale. The equiatomic intermetallic titanium-iron (TiFe) alloy is a prime candidate for stationary hydrogen applications due to its high volumetric storage density, nontoxicity, and safety attributes. However, the conventional synthesis of TiFe alloy relies on high purity titanium and iron metal feedstocks, which must first be extracted from their respective ores before being alloyed in equiatomic ratio. This is a complex, multistep process posing environmental and economic challenges associated with the extraction of metallurgical-grade titanium. Here, we propose an alternate straightforward synthesis pathway for TiFe alloy through the direct calciothermic reduction of ilmenite sand (FeTiO3). Initial small-scale experiments have achieved a maximum TiFe yield of approximately 52 wt %, with similar yields observed when scaling up to 100 g samples. The TiFe alloy produced via this pathway demonstrated a hydrogen storage capacity of approximately 0.71 wt % after activation at 65 bar, indicating that direct metallothermic reduction of ilmenite sand represents an attractive alternative production route for hydrogen storage alloys, which offers economic and sustainability advantages over the existing industrial pathway.