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• Jang, Seong-Hoon; Yao, Yiwen; Liu, Chuanyu; Zhang, Linda; Zhang, Di & Jia, Xue [Show all 69 contributors for this article] (2026). Building a Physics-Aware AI Ecosystem for Solid-State Hydrogen Storage Materials. ACS Energy Letters. 11(9), p. 6007–6025. doi: 10.1021/acsenergylett.6c01856. Full text in Research Archive Show summary

  Abstract Hydrogen storage remains a central bottleneck for scalable hydrogen energy systems due to the multiscale and coupled nature of the thermodynamics, kinetics, and microstructural evolution of hydrogen storage materials (HSMs). Although artificial intelligence (AI) has accelerated materials discovery, current approaches remain constrained by fragmented data, limited physical consistency, and weak integration with experimental validation. Here, we propose a unified framework that integrates coherent data infrastructure, physics-grounded modeling, and AI-driven inverse design within a closed-loop discovery paradigm. By constraining optimization with thermodynamics, kinetics, uncertainty, provenance, and experimental feedback, this approach enables adaptive, physically consistent optimization, thereby establishing a pathway toward autonomous, digital-twin-enabled discovery of HSMs.

• Broom, Darren P.; Allendorf, Mark D.; Autrey, Tom; Baricco, Marcello; Colbe, Jose Bellosta von & Bowden, Mark E. [Show all 33 contributors for this article] (2026). Hydrogen-based materials for energy storage and conversion. Nature Reviews Clean Technology. 2, p. 512–533. doi: 10.1038/s44359-026-00184-z. Full text in Research Archive
• Lunde, Vilde G. S.; Fjellvåg, Øystein S.; Döring, Allan M.; Straßheim, Marc; Pomjakushin, Vladimir & Skokov, Konstantin P. [Show all 12 contributors for this article] (2026). Influence of Ni substitution on phase transitions and magnetocaloric effect of NdCo2 at cryogenic temperatures. Physical review B (PRB). ISSN 2469-9950. 113(18). doi: 10.1103/drsr-yt3j. Full text in Research Archive
• Pavlyuk, Volodymyr; Kordan, Vasyl; Zelinska, Oksana; Pavlyuk, Nazar; Dmytriv, Grygoriy & Silva, Bruno Hessel [Show all 10 contributors for this article] (2026). Hydrogenation properties of composite materials based on yttrium substituted Mg17Al12. Journal of Alloys and Compounds. ISSN 0925-8388. 1057. doi: 10.1016/j.jallcom.2026.186660. Full text in Research Archive
• Lunde, Vilde G. S.; Ofstad, Benedicte; Ohresser, Philippe; Fjellvåg, Øystein Slagtern; Sjåstad, Anja O. & Hauback, Bjørn C. [Show all 7 contributors for this article] (2025). Electronic and magnetic properties of light rare-earth cubic Laves compounds derived from x-ray magnetic circular dichroism. Physical review B (PRB). ISSN 2469-9950. 112(22). doi: 10.1103/hf2c-46t3. Full text in Research Archive Show summary

  This work presents electronic and magnetic properties of selected members in the cubic Laves phase series Nd1−𝑥⁢Pr𝑥⁡CoNi (0 ≤ 𝑥 ≤ 1) and Ce0.25⁢Pr0.75⁡CoNi, together with the corresponding binary compositions (NdCo2, NdNi2, PrCo2, PrNi2, CeCo2, CeNi2), using soft x-ray absorption spectroscopy, x-ray magnetic circular dichroism (XMCD), density-functional theory, and crystal field multiplet calculations. All transition-metal moments saturate below 1 T, while the rare-earth moments do not saturate even at 5 T, consistent with van Vleck paramagnetic contributions and crystal field suppression. While the sum rules are widely used to extract element-specific magnetic moments from XMCD, we show that for 3⁢𝑑 transition metals, their application requires accurate estimates of the number of unoccupied 3⁢𝑑 states. We observe a finite magnetic moment on Ni, challenging the common assumption of its nonmagnetic character in Laves phases. The orbital magnetic moments were determined using the spin rules, while the spin moments were estimated from single-ion values from multiplet calculations, due to the invalidity of the spin sum rule for light rare-earth elements. The magnetic moments of Nd and Pr are found to be suppressed relative to their free-ion values, with multiplet theory indicating that this is due to crystal field effects. Our results confirm that Nd and Pr maintain localized 4⁢𝑓3 and 4⁢𝑓2 configurations, respectively, and that their element-specific magnetic moments are robust to rare-earth substitution. Ce, on the other hand, exhibits a tuneable mixed-valent ground state with both magnetic 4⁢𝑓1 and nonmagnetic 4⁢𝑓0 components. The relative fraction of these states varies with the electronegativity of the surrounding 3⁢𝑑 transition metals, revealing a pathway to tune Ce magnetism via composition. This work establishes a framework for accurately interpreting XMCD in light rare-earth-based intermetallics and provides insight for designing light rare-earth-based magnetocaloric materials.

• Kim, Stephen; Sugai, Cody; Hauback, Bjørn Christian; Fjellvåg, Øystein Slagtern; Bradley, John P. & Ishii, Hope A. [Show all 8 contributors for this article] (2025). Enhanced hydrogenation kinetics of magnesium diboride through carbon substitution into the boride layers. Journal of Materials Chemistry A. ISSN 2050-7488. 13(48), p. 41896–41902. doi: 10.1039/d5ta07495a. Full text in Research Archive
• Fjellvåg, Øystein Slagtern; Saha, Dipankar; Chernyshov, Dmitry; Bernal, Fabian Leonardo Martinez; Fjellvåg, Helmer & Hauback, Bjørn Christian [Show all 7 contributors for this article] (2025). On the low temperature crystal structure of KCrF3. Journal of Solid State Chemistry. ISSN 0022-4596. 352. doi: 10.1016/j.jssc.2025.125558. Full text in Research Archive Show summary

  We report on the low-temperature phase transition and crystal structure of KCrF3, revisiting the previously reported reentrant tetragonal transition at 5 K. Using high-resolution X-ray powder diffraction across a temperature range of 5–300 K in two independent experiments, we study the structural developments and apply symmetry-mode analysis to describe the transition from tetragonal to monoclinic. A tilt of the CrF6-octahedra drives the symmetry reduction. Evaluation of the bond lengths and angles shows no sign of a reentrant or incipient transition. Our findings confirm that the low-temperature phase of KCrF3 is monoclinic.

• Fjellvåg, Øystein Slagtern; Park, Heesoo; Veillon, Fabien; Lyu, Jike; Medarde, Marisa & Amedi, Salah Bra [Show all 10 contributors for this article] (2025). ACrF3 Jahn–Teller-Distorted Fluoroperovskites: Expanding to RbCrF3 and CsCrF3. Inorganic Chemistry. ISSN 0020-1669. 64(36), p. 18316–18322. doi: 10.1021/acs.inorgchem.5c02668. Full text in Research Archive Show summary

  The Jahn–Teller effect significantly affects the CrF6 octahedra in Cr(II) fluoroperovskites. Here, we report the synthesis, crystal structures, and magnetic properties of RbCrF3 and CsCrF3, thereby completing a comprehensive investigation of the ACrF3 fluoroperovskites. Powder samples are prepared using a wet-chemical method, which allows stabilization of Cr(II). RbCrF3 predominantly adopts the P4/mbm space group; however, the absence of the expected (211) peak suggests a limited correlation length, and we demonstrate that this is a result of stacking faults in the rotation of the distorted CrF6 octahedra along the c-axis. We estimate around 5–10% of I4/mcm-type stacking in P4/mbm for RbCrF3. In contrast, CsCrF3 showcases a two-phase coexistence of I4/mcm and P4/mbm polymorphs and, as such, parallels to KCuF3. We discuss and highlight the interplay between the impact of A-site cations and the Jahn–Teller effect acting on CrF6 octahedra. Antiferromagnetic interactions dominate the paramagnetic regime, and RbCrF3 and CsCrF3 both have a Weiss temperature of −12 K, associated with Néel temperatures of 50 and 47 K, respectively. The effective paramagnetic moments of 4.65 and 4.68 μB for RbCrF3 and CsCrF3 are in good agreement with S = 2 spin configuration.

• Silva, Valmir Rodrigo da; Fjellvåg, Øystein Slagtern; Švec, Peter; Jr., Peter Švec,; Hauback, Bjørn Christian & Deledda, Stefano (2025). The Effect of Mo and Al Substitution in Cryomilled and Cold-Rolled FeNi Alloys. Metals. 15(9), p. 996–996. doi: 10.3390/met15090996. Full text in Research Archive Show summary

  The ordered tetragonal FeNi L10 phase, tetrataenite, is a promising candidate for rare earth-free permanent magnets due to its competitive magnetic properties and the low cost of the constituent elements. In this work, we have investigated the effect of molybdenum and aluminum substitution on the formation of the ordered L10 phase. The alloys were prepared with die casting and melt spinning techniques, further processed using cold rolling and cryomilling, and finally annealed below the estimated order–disorder temperature (TOD). To study the influence of composition and processing of the alloys, structural characterization and microstructural analysis were performed with synchrotron radiation X-ray diffractometry (SR-PXD) and Scanning Transmission Electron Microscopy (STEM), respectively. The presence of tetrataenite in the alloys investigated in this work could not be confirmed. In situ SR-PXD and STEM indicated minimal structural changes in the temperature stability range of the materials. A full-loop hysteresis curve acquired using a vibrating sample magnetometer (VSM) indicated no signs of magnetic hardening of the alloys with the measured coercivity being below 10 Oe, and thus consistent with FeNi without ordering.

• Lunde, Vilde Sturtzel; Møller, Amalie Bisgaard; Eggert, Bruno Guilherme Fischer; Döring, Allan M.; Grivel, Jean-Claude & Bjørk, Rasmus [Show all 12 contributors for this article] (2025). Machine learning guided discovery and experimental validation of light rare earth Laves phases for magnetocaloric hydrogen liquefaction. Acta Materialia. ISSN 1359-6454. 297. doi: 10.1016/j.actamat.2025.121282. Full text in Research Archive Show summary

  In the search for new compounds suited for magnetocaloric hydrogen liquefaction, we have combined machine learning (ML) predictions with experiments. Two series of cubic C15 Laves phases, and (0 ≤ x ≤ 1), were selected based on Curie temperature (Tc) predictions of three ML models. A superior model performance was obtained when the dataset was developed for a specific crystal class, despite it being limited to only containing 265 compounds. The random forest regression, gradient boosting regression, and neural network ML models yielded mean absolute errors of 14, 18, and 20 K, respectively. These errors are low compared to previously reported Tc-predictions using ML. The models are powerful tools for the initial screening of new candidate materials, and the accuracy for light rare earth based cubic Laves compounds will improve as the dataset increases. The selected compounds based on the ML screening were synthesized by arc melting and characterized for potential magnetocaloric hydrogen liquefaction applications. The compositions showed magnetic ordering between 20 and 36 K, thus in the lower temperature region relevant for magnetocaloric hydrogen liquefaction. Moreover, they exhibited magnetic entropy change ranging from 6.0 to 7.2 Jkg−1K−1 and adiabatic temperature change from 2.2 to 2.6 K, for a field of 5 T. In contrast, the Ce-containing compounds exhibited a mixture of magnetic Ce and non-magnetic Ce, yielding low magnetization, thus low magnetocaloric effect, and magnetic ordering temperatures below 20 K.

• Toft-Petersen, Rasmus; Tucker, Gregory S.; Whitelegg, Liam; Krighaar, Kristine Marie Løfgren; Gallo, Tamires & Marko, Marton [Show all 37 contributors for this article] (2025). BIFROST—An indirect geometry cold neutron spectrometer at the European Spallation Source. Review of Scientific Instruments. ISSN 0034-6748. 96(4). doi: 10.1063/5.0258847. Full text in Research Archive
• Eggert, Bruno Guilherme Fischer; Delczeg-Czirjak, E.K.; Fjellvåg, Øystein Slagtern; Hauback, Bjørn Christian & Frommen, Christoph (2024). Structure and magnetism of Fe-substituted MnNiSi<inf>0.95</inf>Al<inf>0.05</inf>. Materialia. 39. doi: 10.1016/j.mtla.2024.102321. Full text in Research Archive
• Erhan, Raul-Victor; Haan, Viktor-Otto de; Frommen, Christoph; Knudsen, Kenneth Dahl; Llamas-Jansa, Isabel & Hauback, Bjørn Christian (2024). A Concept for a Multipurpose Time-of-Flight Neutron Reflectometer at Compact Neutron Sources. Instruments. 8(2). doi: 10.3390/instruments8020030. Full text in Research Archive Show summary

  The design of a time-of-flight neutron reflectometer proposed for the new generation of compact neutron sources is presented. The reflectometer offers the possibility to use spin-polarized neutrons. The reflectometer design presented here takes advantage of a cold neutron source and uses neutrons with wavelengths in the range of 2–15 Å for the unpolarized mode. In general, due to tight spatial restrictions and the need to avoid moving parts inside the beam channel, a multi-channel collimator guide and reflective neutron guide are used for the first section of the instrument. This enables definition of the desired wavelength band and easy selection of one out of three different Q-resolutions. A low background for the collimator system and the reflectometer is ensured by employing a tangential beam channel and an in-channel sapphire filter. The second section is the time-of-flight (TOF) system, which uses a double-disk neutron chopper followed by polarization elements, the sample environment and the neutron detector system. Monte Carlo simulations and neutron beamline intensity measurements are presented. The design considerations are adoptable for neutron sources where space is limited and sections of the instrument are in a high-radiation environment.

• Fjellvåg, Øystein Slagtern; Gonano, Bruno; Bernal, Fabian Leonardo Martinez; Amedi, Salah Bra; Lyu, Jike & Pomjakushin, Vladimir [Show all 12 contributors for this article] (2024). Order-to-Disorder Transition and Hydrogen Bonding in the Jahn-Teller Active NH4CrF3 Fluoroperovskite. Inorganic Chemistry. ISSN 0020-1669. 63(23), p. 10594–10602. doi: 10.1021/acs.inorgchem.4c00931. Full text in Research Archive Show summary

  Large quantities of high-purity NH4CrF3 have been synthesized using a wet-chemical method, and its structural chemistry and magnetic properties are investigated in detail for the first time. NH4CrF3 is a tetragonal fluoroperovskite that displays an ordering of the ammonium (NH4+) groups at room temperature and C-type orbital ordering. The ammonium groups order and display distinct signs of hydrogen bonds to nearby fluoride anions by buckling the Cr–F–Cr angle away from 180°. The ammonium ordering remains up to 405 K, much higher than in other ammonium fluoroperovskites, indicating a correlation between the flexibility of the Jahn–Teller ion, the hydrogen bond formation, and the ammonium ordering. At 405 K, an order-to-disorder transition occurs, where the ammonium groups disorder, corresponding to a transition to higher symmetry. This is accompanied by a contraction of the unit cell from breaking hydrogen bonds, similar to the phenomenon observed in water ice melting. The compound orders antiferromagnetically with a Neél temperature of 60 K, an effective paramagnetic moment of 4.3 μB, and a Weiss temperature of −33 K. An A-type antiferromagnetic structure is identified by neutron diffraction, with an ordered moment of 3.72(2) μB.

• Silva, Valmir Rodrigo da; Fjellvåg, Øystein Slagtern; Pokle, Anuj; Hauback, Bjørn Christian & Deledda, Stefano (2024). Effect of Carbon Addition and Mechanical Activation on FeNi Alloys for Permanent Magnet Applications. Metals. 14(10). doi: 10.3390/met14101125. Full text in Research Archive Show summary

  Tetrataenite is a promising candidate for rare earth-free permanent magnets due to its low cost and intrinsic magnetic properties. This work investigates the effect of combined milling at liquid nitrogen temperatures (cryomilling) and the addition of carbon as an interstitial element for promoting the formation of tetrataenite. Crystal structure, microstructure, and magnetic properties are investigated to understand the influence of mechanical processing and compositional modifications. No unambiguous evidence of the ordered phase of tetrataenite is found in the structural characterization. However, using Scanning Transmission Electron Microscopy (STEM) and powder X-ray diffraction (PXD) analyses, the occurrence of both twinning and stacking faults resulting from the high-energy milling process is observed, which is a relevant factor for identifying tetrataenite in FeNi alloys. The probability of a stacking fault and twinning occurring for a carbon-free FeNi sample before annealing is found to be 2% and 1.4%, respectively. After annealing, the stacking fault probability decreased to 1.2%, while that of twinning was 1.4%. By increasing the carbon concentration to 5 at.%, the stacking faults and twinning probabilities decrease slightly to 1.2% and 1.3%, respectively. The occurrence of stacking faults combined with small crystallite sizes was a hindering factor in identifying the presence of tetrataenite.

• Eggert, Bruno Guilherme Fischer; Delczeg-Czirjak, Erna K.; Hauback, Bjørn Christian & Frommen, Christoph (2023). Magnetic transitions in V-Fe-Co-Ni-Cu-based high entropy alloys. Materials Today Physics. 35. doi: 10.1016/j.mtphys.2023.101116. Full text in Research Archive Show summary

  FeCoNi, V0.85FeCoNi, FeCoNiCu1.15 and V0.85FeCoNiCu1.15 alloys have been synthesized by arc melting and analyzed by powder X-ray diffraction, electron microscopy, magnetic measurements, and density functional theory (DFT). The influence of each alloying element on the magnetic exchange interaction, Curie temperature (TC) and magnetocaloric effect is evaluated. The experimental results show that Cu and V “dilute” the magnetic properties and couple antiferromagnetically to Fe, Co, and Ni. Analysis of the microstructure reveals a lack of solubility between V and Cu with FeCoNi, and between themselves, thus lowering the concentration of V and Cu in the main solid solution of the 5-element alloy V0.85FeCoNiCu1.15. Tc decreases significantly from 997 K in FeCoNi to 245 K in V0.85FeCoNi and 297 K in V0.85FeCoNiCu1.15, respectively. The derivative of magnetization as a function of temperature (dM/dT) in the vicinity of Tc is drastically reduced due to the presence of V which indicates a reduced magnetocaloric effect. DFT calculations confirm antiferromagnetic coupling of V to the ferromagnetic FeCoNi-base and predict a similar behavior for other transition metal elements (e.g., Ti, Cr, Mn). This leads to a lowering of Tc, which is needed to establish the magnetocaloric effect at room temperature. However, it comes at a cost of reduced magnetic moments. Nevertheless, the use of V and Cu has shown possible routes for tuning the magnetocaloric effect in FeCoNi-based high entropy alloys.

• Wu, Hui; Zhou, Wei; Udovic, Terrence J.; Jr., Robert C. Bowman, & Hauback, Bjørn Christian (2023). Characterizing the ZrBe<inf>2</inf>H<inf>x</inf> Phase Diagram via Neutron Scattering Methods. Inorganics. 11(1). doi: 10.3390/inorganics11010001. Full text in Research Archive
• Eggert, Bruno G. F.; Wang, Kun; Jafarzadeh, Sina; Bahl, Christian R.; Hauback, Bjørn Christian & Frommen, Christoph (2023). Study of the magnetostructural transition in critical-element free Mn<inf>1-x</inf>Ni<inf>1-x</inf>Fe<inf>2x</inf>Si<inf>0.95</inf>Al<inf>0.05</inf>. AIP Advances. 13(2). doi: 10.1063/9.0000511. Full text in Research Archive
• Eggert, Bruno Guilherme Fischer; Belo, J.F.H.; Araujo, J.P.; Hauback, Bjørn Christian & Frommen, Christoph (2023). Structural transitions and magnetocaloric properties of low-cost MnNiSi-based intermetallics. Intermetallics (Barking). ISSN 0966-9795. 154. doi: 10.1016/j.intermet.2023.107823. Full text in Research Archive
• Echevarria-Bonet, Cristina; Garrido-Alvarez, J.L.; Martinez-Blanco, D.; Gorria, P.; Sørby, Magnus Helgerud & Riktor, Marit Dalseth [Show all 8 contributors for this article] (2023). Anharmonicity effects and thermal expansion of thermoelectric (M,M’,M”)NiSn (M,M’,M”=Ti, Zr, Hf) half-Heusler alloys. Journal of Alloys and Compounds. ISSN 0925-8388. 959. doi: 10.1016/j.jallcom.2023.170583. Full text in Research Archive
• Pasquini, Luca; Sakaki, Kouji; Akiba, Etsuo; Allendorf, Mark D.; Alvares, Ebert & Ares, José R. [Show all 59 contributors for this article] (2022). Magnesium- and intermetallic alloys-based hydrides for energy storage: modelling, synthesis and properties. Progress in Energy. 4(3). doi: 10.1088/2516-1083/ac7190. Full text in Research Archive Show summary

  Abstract Hydrides based on magnesium and intermetallic compounds provide a viable solution to the challenge of energy storage from renewable sources, thanks to their ability to absorb and desorb hydrogen in a reversible way with a proper tuning of pressure and temperature conditions. Therefore, they are expected to play an important role in the clean energy transition and in the deployment of hydrogen as an efficient energy vector. This review, by experts of Task 40 ‘Energy Storage and Conversion based on Hydrogen’ of the Hydrogen Technology Collaboration Programme of the International Energy Agency, reports on the latest activities of the working group ‘Magnesium- and Intermetallic alloys-based Hydrides for Energy Storage’. The following topics are covered by the review: multiscale modelling of hydrides and hydrogen sorption mechanisms; synthesis and processing techniques; catalysts for hydrogen sorption in Mg; Mg-based nanostructures and new compounds; hydrides based on intermetallic TiFe alloys, high entropy alloys, Laves phases, and Pd-containing alloys. Finally, an outlook is presented on current worldwide investments and future research directions for hydrogen-based energy storage.

• Dematteis, Erika Michela; Amdisen, Mads B.; Autrey, Tom; Barale, Jussara; Bowden, Mark E. & Buckley, Craig E. [Show all 32 contributors for this article] (2022). Hydrogen storage in complex hydrides: past activities and new trends. Progress in Energy. 4(3). doi: 10.1088/2516-1083/ac7499. Full text in Research Archive
• Eggert, Bruno G. F.; Delczeg-Czirjak, Erna K.; Maccari, Fernando; Kumar, Susmit; Gutfleisch, Oliver & Fjellvåg, Helmer [Show all 8 contributors for this article] (2022). Exploring V-Fe-Co-Ni-Al and V-Fe-Co-Ni-Cu high entropy alloys for magnetocaloric applications. Journal of Alloys and Compounds. ISSN 0925-8388. 921. doi: 10.1016/j.jallcom.2022.166040. Full text in Research Archive Show summary

  A series of V1−x-Fe-Co-Ni-Al1+x and V1−x-Fe-Co-Ni-Cu1+x high entropy alloys with varying compositions (0 ≤ x ≤ 0.75) has been investigated for magnetocaloric applications. Compositions were selected according to established properties, such as configurational entropy, atomic size difference, and enthalpy of mixing. To study the influence of composition on magnetic ordering temperatures, the V and (Al/Cu) contents were changed while the content of Fe, Co and Ni was retained at 20 at. % each. The crystal structure and microstructure of the as-cast alloys were compared to literature phase guidelines and thermodynamic calculations based on the CALPHAD approach. The V-Fe-Co-Ni-Al compounds are monophasic and crystallize in a disordered body centered cubic structure or its ordered B2 variant, while the V-Fe-Co-Ni-Cu compounds are all multiphasic. Magnetic transitions in the V-Fe-Co-Ni-Al system span over 400 K, with Curie temperature ranging from 155 K in equiatomic VFeCoNiAl, to 456 K in non-equiatomic V0.25FeCoNiAl1.75. The V-Fe-Co-Ni-Cu alloys display magnetic transitions that span about 150 K, with Curie temperature ranging from 230 K for equiatomic VFeCoNiCu to 736 K for non-equiatomic V0.25FeCoNiCu1.75. The magnetic properties of the V-Fe-Co-Ni-Cu compounds were evaluated by means of density functional theory. Individual element-specific moments, magnetic exchange integrals between atomic pairs, and Curie temperatures were calculated. V0.85FeCoNiCu1.15 is selected due to its Curie temperature of 329 K, and its calculated isothermal entropy change of 0.75 J/kg.K for a field change of 5 T is comparable to other 3d metal-based high entropy alloys that form disordered solid solutions.

• Cuevas, Fermin; Amdisen, Mads B.; Baricco, Marcello; Buckley, Craig E.; Cho, Young Whan & Jongh, Petra E. de [Show all 31 contributors for this article] (2022). Metallic and complex hydride-based electrochemical storage of energy. Progress in Energy. 4(3). doi: 10.1088/2516-1083/ac665b. Full text in Research Archive Show summary

  Abstract The development of efficient storage systems is one of the keys to the success of the energy transition. There are many ways to store energy, but among them, electrochemical storage is particularly valuable because it can store electrons produced by renewable energies with a very good efficiency. However, the solutions currently available on the market remain unsuitable in terms of storage capacity, recharging kinetics, durability, and cost. Technological breakthroughs are therefore expected to meet the growing need for energy storage. Within the framework of the Hydrogen Technology Collaboration Program—H 2 TCP Task-40, IEA’s expert researchers have developed innovative materials based on hydrides (metallic or complex) offering new solutions in the field of solid electrolytes and anodes for alkaline and ionic batteries. This review presents the state of the art of research in this field, from the most fundamental aspects to the applications in battery prototypes.

• Sørby, Magnus Helgerud; Martinsen, Fredrik Aleksander; Karazhanov, Smagul; Hauback, Bjørn Christian & Marstein, Erik Stensrud (2022). On the Crystal Chemistry of Photochromic Yttrium Oxyhydride. Energies. 15(5). doi: 10.3390/en15051903. Full text in Research Archive
• Perizat, Berdiyeva; Karabanova, Anastasiia; Blanchard, Didier; Hauback, Bjørn & Deledda, Stefano (2021). Sr(NH<inf>3</inf>)<inf>8</inf>Cl<inf>2</inf>-Expanded Natural Graphite composite for thermochemical heat storage applications studied by in-situ neutron imaging. Journal of Energy Storage. ISSN 2352-152X. 34. doi: 10.1016/j.est.2020.102176. Full text in Research Archive
• Ek, Gustav; Nygård, Magnus Moe; Pavan, Adriano F.; Montero, Jorge; Henry, Paul F. & Sørby, Magnus Helgerud [Show all 11 contributors for this article] (2021). Elucidating the Effects of the Composition on Hydrogen Sorption in TiVZrNbHf-Based High-Entropy Alloys. Inorganic Chemistry. ISSN 0020-1669. 60(2), p. 1124–1132. doi: 10.1021/acs.inorgchem.0c03270. Full text in Research Archive
• Zavorotynska, Olena; Sørby, Magnus Helgerud; Vitillo, Jenny G.; Deledda, Stefano; Frommen, Christoph & Hauback, Bjørn Christian (2021). Experimental and computational characterization of phase transitions in CsB3H8. Physical Chemistry, Chemical Physics - PCCP. ISSN 1463-9076. 23, p. 17836–17847. doi: 10.1039/d1cp02189c. Full text in Research Archive
• Nygård, Magnus Moe; Fjellvåg, Øystein; Sørby, Magnus Helgerud; Sakaki, Kouji; Ikeda, Kazutaka & Armstrong, Jeff [Show all 12 contributors for this article] (2021). The average and local structure of TiVCrNbDx (x = 0, 2.2, 8) from total scattering and neutron spectroscopy. Acta Materialia. ISSN 1359-6454. 205, p. 1–15. doi: 10.1016/j.actamat.2020.116496. Full text in Research Archive Show summary

  The volumetric hydrogen density of 160 kg H/m 3 in TiVCrNbH 8 is among the highest for interstitial hy- drides, but the reported reversible capacity is only about 2/3 of the full theoretical capacity at room temperature. In the present work we have investigated the local structure in TiVCrNbD x , x = 0 , 2.2, 8 with the aim to unravel how the remaining sites can be destabilized with respect to hydrogen/deuterium occupation using total scattering measurements and Reverse Monte Carlo (RMC) structure modelling. Our analysis indicates that the partially desorbed deuteride ( x = 2 . 2 ) adopts a body-centred tetragonal struc- ture ( I4 /mmm ) where the deuterium atoms occupy both tetrahedral and octahedral interstices with low occupancies. There is a significantly higher portion of occupied sites with nearest-neighbour metals with low valence-electron concentration VEC . This observation is used to motivate strategies for further desta- bilization of the hydride. Inelastic neutron scattering (INS) and density functional theory (DFT) calcula- tions indicate that the vibrational density of states is very diverse in TiVCrNbH 2 . 4 , and it is suggested that the hydrogen atoms might be mobile between nearby interstices.

• Hirscher, Michael; Yartys, Volodymyr; Baricco, Marcello; Colbe, Jose Bellosta von; Blanchard, Didier & Bowman, Robert C. [Show all 48 contributors for this article] (2020). Materials for hydrogen-based energy storage – Past, recent progress and future outlook. Journal of Alloys and Compounds. ISSN 0925-8388. 827. doi: 10.1016/j.jallcom.2019.153548. Full text in Research Archive
• Pal, Santosh Kumar; Frommen, Christoph; Kumar, Susmit; Hauback, Bjørn; Fjellvåg, Helmer & Helgesen, Geir (2020). Enhancing giant magnetocaloric effect near room temperature by inducing magnetostructural coupling in Cu-doped MnCoGe. Materials & design. ISSN 0264-1275. 195, p. 1–11. doi: 10.1016/j.matdes.2020.109036. Full text in Research Archive Show summary

  High performance magnetocaloric materials are crucial to realize the energy efficient and environment friendly magnetic cooling/refrigeration technology. We have designed Mn1-xCuxCoGe compounds possessing a giant magnetocaloric effect near room temperature. The magnetic and structural degree of freedom have been coupled by substituting Cu for Mn leading to a first-order magnetostructural phase transformation resulting in a giant magnetocaloric effect over a wide temperature window of 100 K (250–350 K). A very large entropy change value of 58 J.kg−1.K−1 corresponding to a magnetic field change of 5 T near room temperature has been obtained for Mn0.89Cu0.11CoGe exhibiting a maximum effective refrigerant capacity of 258.2 J.kg−1. The first-order magnetostructural phase transformation which is essential for the giant magnetocaloric effect has been confirmed by a combinatorial master-curve and Arrott-plot analyses. The results of giant magnetocaloric effect realized in Mn1-xCuxCoGe are comparable to or better than that of the other reported high performing materials, and this material can be of significant importance for the development of environment friendly and energy efficient cooling devices. The approach of magnetostructural coupling by tuning the structural and magnetic transitions for a giant magnetocaloric effect can also be adopted for other materials to design the best solid-state magnetic refrigerant.

• El-Kharbachi, Abdelouahab; Dematteis, Erika Michela; Shinzato, Keita; Stevenson, Siobhan C.; Bannenberg, Lars J. & Heere, Michael [Show all 14 contributors for this article] (2020). Metal Hydrides and Related Materials. Energy Carriers for Novel Hydrogen and Electrochemical Storage. Journal of Physical Chemistry C. ISSN 1932-7447. 124(14), p. 7599–7607. doi: 10.1021/acs.jpcc.0c01806. Full text in Research Archive
• Bannenberg, L. J.; Heere, Michael; Benzidi, Hind; Montero, J.; Dematteis, Erika Michela & Suwarno, S. [Show all 26 contributors for this article] (2020). Metal (boro-) hydrides for high energy density storage and relevant emerging technologies. International Journal of Hydrogen Energy. ISSN 0360-3199. 45(58), p. 33687–33730. doi: 10.1016/j.ijhydene.2020.08.119. Full text in Research Archive Show summary

  The current energy transition imposes a rapid implementation of energy storage systems with high energy density and eminent regeneration and cycling efficiency. Metal hydrides are potential candidates for generalized energy storage, when coupled with fuel cell units and/or batteries. An overview of ongoing research is reported and discussed in this review work on the light of application as hydrogen and heat storage matrices, as well as thin films for hydrogen optical sensors. These include a selection of single-metal hydrides, Ti–V(Fe) based intermetallics, multi-principal element alloys (high-entropy alloys), and a series of novel synthetically accessible metal borohydrides. Metal hydride materials can be as well of important usefulness for MH-based electrodes with high capacity (e.g. MgH2 ~ 2000 mA h g−1) and solid-state electrolytes displaying high ionic conductivity suitable, respectively, for Li-ion and Li/Mg battery technologies. To boost further research and development directions some characterization techniques dedicated to the study of M-H interactions, their equilibrium reactions, and additional quantification of hydrogen concentration in thin film and bulk hydrides are briefly discussed.

• Qviller, Atle Jorstad; Frommen, Christoph; Hauback, Bjørn; Magnus, F.; Kirkby, B. J. & Hjörvarsson, B. (2020). Direct observation of magnetic proximity effects in amorphous exchange-spring magnets by neutron reflectometry. PHYSICAL REVIEW MATERIALS. 4(10). doi: 10.1103/PhysRevMaterials.4.104404. Full text in Research Archive
• Barale, Jussara; Deledda, Stefano; Dematteis, Erika Michela; Sørby, Magnus Helgerud; Baricco, Marcello & Hauback, Bjørn (2020). Synthesis and characterization of Magnesium-Iron-Cobalt complex hydrides. Scientific Reports. 10(1). doi: 10.1038/s41598-020-65774-8. Full text in Research Archive
• Nygård, Magnus Moe; Sørby, Magnus Helgerud; Grimenes, Arne Auen & Hauback, Bjørn (2020). The Influence of Fe on the Structure and Hydrogen Sorption Properties of Ti-V-Based Metal Hydrides. Energies. 13(11). doi: 10.3390/en13112874. Full text in Research Archive Show summary

  Ti-V-based metal hydrides have decent overall performance as hydrogen storage materials, but V is expensive and it is therefore tempting to replace it by less expensive ferrovanadium containing about 20% Fe. In the present work we have investigated how Fe influences the structure and hydrogen storage properties of (Ti0.7V0.3)1−zFez alloys with errortypecez∈{0, 0.03, 0.06, 0.1, 0.2, 0.3} using synchrotron radiation powder X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry and manometric measurements performed in a Sieverts apparatus. The alloys form body-centered cubic (bcc) crystal structures for all considered values of z, and the addition of Fe causes the unit cell to contract. When exposed to hydrogen gas, the bcc alloys form face-centered cubic (fcc) hydrides if errortypecez≤0.1 while other hydrogen-containing phases are formed for higher Fe-contents. The hydrogen capacities of the fcc hydrides at 20 bar are not significantly influenced by the addition of Fe and reach 3.2(3) wt% in (Ti0.7V0.3)0.9Fe0.1H1.6(2). For higher Fe contents the hydrogen capacity is decreased. The absorption kinetics are fast and the reactions are complete within minutes when the alloys are exposed to 20 bar H2 at room temperature. Increasing Fe content reduces the desorption enthalpy, onset temperature and activation energy.

• Andersen, Ken H.; Argyriou, Dimitri N.; Jackson, Andrew J.; Houston, Judith E.; Henry, Paul F. & Deen, Pascale P. [Show all 49 contributors for this article] (2020). The instrument suite of the European Spallation Source. Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment. ISSN 0168-9002. 957. doi: 10.1016/j.nima.2020.163402. Full text in Research Archive
• El-Kharbachi, Abdelouahab; Wind, Julia; Ruud, Amund; Høgset, Astrid Bygdås; Nygård, Magnus Moe & Zhang, Junxian [Show all 14 contributors for this article] (2020). Pseudo-ternary LiBH4-LiCl-P2S5 system as structurally disordered bulk electrolyte for all-solid-state lithium batteries. Physical Chemistry, Chemical Physics - PCCP. ISSN 1463-9076. 22(25), p. 13872–13879. doi: 10.1039/d0cp01334j. Full text in Research Archive Show summary

  The properties of the mixed system LiBH4–LiCl–P2S5 are studied with respect to all-solid-state batteries. The studied material undergoes an amorphization upon heating above 60 °C, accompanied with increased Li+ conductivity beneficial for battery electrolyte applications. The measured ionic conductivity is ∼10−3 S cm−1 at room temperature with an activation energy of 0.40(2) eV after amorphization. Structural analysis and characterization of the material suggest that BH4 groups and PS4 may belong to the same molecular structure, where Cl ions interplay to accommodate the structural unit. Thanks to its conductivity, ductility and electrochemical stability (up to 5 V, Au vs. Li+/Li), this new electrolyte is successfully tested in battery cells operated with a cathode material (layered TiS2, theo. capacity 239 mA h g−1) and Li anode resulting in 93% capacity retention (10 cycles) and notable cycling stability under the current density ∼12 mA g−1 (0.05C-rate) at 50 °C. Further advanced characterisation by means of operando synchrotron X-ray diffraction in transmission mode contributes explicitly to a better understanding of the (de)lithiation processes of solid-state battery electrodes operated at moderate temperatures.

• Heere, Michael; Hansen, Anna-Lena; Payandeh, SeyedHosein; Aslan, Neslihan; Gizer, Gökhan & Sørby, Magnus Helgerud [Show all 10 contributors for this article] (2020). Dynamics of porous and amorphous magnesium borohydride to understand solid state Mg-ion-conductors. Scientific Reports. 10(1). doi: 10.1038/s41598-020-65857-6. Full text in Research Archive
• Mauroy, Henrik; Klyukin, Konstantin; Shelyapina, Marina G.; Keen, David A.; Thøgersen, Annett & Hauback, Bjørn [Show all 7 contributors for this article] (2020). Short-Range Structure of Ti0.63V0.27Fe0.10D1.73 from Neutron Total Scattering and Reverse Monte Carlo Modelling. Energies. 13(8). doi: 10.3390/en13081947. Full text in Research Archive Show summary

  Ti-V-based body-centered cubic (BCC) alloys have potential for large-scale hydrogen storage if expensive vanadium is substituted with much cheaper Fe-containing ferrovanadium. Use of ferrovanadium reduces the alloys’ hydrogen storage capacity. This is puzzling since the amount of Fe is low and hydrogen atoms are accommodated in interstitial sites which are partly coordinated by Fe in many intermetallic compounds. The present work is aimed at finding a structural explanation for Fe-induced capacity loss in Ti-V alloys. Since such alloys and their hydrides are highly disordered without long-range occupational order of the different metal species, it was necessary to employ a technique which is sensitive to local structure. Neutron total scattering coupled with reverse Monte Carlo modelling was thus employed to elucidate short-range atomic correlations in Ti0.63V0.27Fe0.10D1.73 from the pair distribution function. It was found that Fe atoms form clusters and that the majority of the vacant interstitial sites are within these clusters. These clusters take the same face-centered cubic structure as the Ti-V matrix in the deuteride and thus they are not simply unreacted Fe which has a BCC structure. The presence of Fe clusters is confirmed by transmission electron microscopy. Density functional theory calculations indicate that the clustering is driven by thermodynamics.

• Perizat, Berdiyeva; Karabanova, Anastasiia; Grinderslev, Jakob B.; Johnsen, Rune E.; Blanchard, Didier & Hauback, Bjørn [Show all 7 contributors for this article] (2020). Synthesis, Structure and NH3 Sorption Properties of Mixed Mg1-xMnx(NH3)6Cl2 Ammines. Energies. 13(11). doi: 10.3390/en13112746. Full text in Research Archive
• Casillas-Trujillo, Luis; Jansson, Ulf; Sahlberg, Martin; Ek, Gustav; Nygård, Magnus Moe & Sørby, Magnus Helgerud [Show all 9 contributors for this article] (2020). Interstitial carbon in bcc HfNbTiVZr high-entropy alloy from first principles. PHYSICAL REVIEW MATERIALS. 4. doi: 10.1103/PhysRevMaterials.4.123601. Full text in Research Archive
• Perizat, Berdiyeva; Karabanova, Anastasiia; Makowska, Malgorzata G.; Johnsen, Rune E.; Blanchard, Didier & Hauback, Bjørn [Show all 7 contributors for this article] (2020). In-situ neutron imaging study of NH3 absorption and desorption in SrCl2 within a heat storage prototype reactor. Journal of Energy Storage. ISSN 2352-152X. 29. doi: 10.1016/j.est.2020.101388. Full text in Research Archive
• Nygård, Magnus Moe; Sławiński, Wojciech A.; Ek, Gustav; Sørby, Magnus Helgerud; Sahlberg, Martin & Keen, David A. [Show all 7 contributors for this article] (2020). Local order in high-entropy alloys and associated deuterides – a total scattering and Reverse Monte Carlo study. Acta Materialia. ISSN 1359-6454. 199, p. 504–513. doi: 10.1016/j.actamat.2020.08.045. Full text in Research Archive
• Llamas-Jansa, Isabel; Kalantzopoulos, Georgios N.; Nordholm, Kari & Hauback, Bjørn (2020). Destabilization of NaBH4 by Transition Metal Fluorides. Molecules. ISSN 1431-5157. 25(4). doi: 10.3390/molecules25040780. Full text in Research Archive
• Llamas-Jansa, Isabel; Friedrichs, Oliver; Fichtner, Maximilian; Bardají, Elisa Gil; Züttel, Andreas & Hauback, Bjørn (2020). Effects of Ball Milling and TiF3 Addition on the Dehydrogenation Temperature of Ca(BH4)2 Polymorphs. Energies. 13(18). doi: 10.3390/en13184828. Full text in Research Archive
• Latroche, Michel; Blanchard, Didier; Cuevas, Fermìn; El-Kharbachi, Abdelouahab; Hauback, Bjørn & Jensen, Torben R. [Show all 13 contributors for this article] (2019). Full-cell hydride-based solid-state Li batteries for energy storage. International Journal of Hydrogen Energy. ISSN 0360-3199. 44(15), p. 7875–7887. doi: 10.1016/j.ijhydene.2018.12.200. Full text in Research Archive
• Nygård, Magnus Moe; Ek, Gustav; Karlsson, Dennis; Sørby, Magnus Helgerud; Sahlberg, Martin & Hauback, Bjørn (2019). Counting electrons - A new approach to tailor the hydrogen sorption properties of high-entropy alloys. Acta Materialia. ISSN 1359-6454. 175, p. 121–129. doi: 10.1016/j.actamat.2019.06.002. Full text in Research Archive
• Nygård, Magnus Moe; Ek, Gustav; Karlsson, Dennis; Sahlberg, Martin; Sørby, Magnus Helgerud & Hauback, Bjørn (2019). Hydrogen storage in high-entropy alloys with varying degree of local lattice strain. International Journal of Hydrogen Energy. ISSN 0360-3199. 44(55), p. 29140–29149. doi: 10.1016/j.ijhydene.2019.03.223. Full text in Research Archive Show summary

  We have investigated the structure and hydrogen storage properties of a series of Ti, V, Zr, Nb and Ta based high-entropy alloys (HEAs) with varying degree of local lattice strain by means of synchrotron radiation powder X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry and manometric measurements in a Sieverts apparatus. The obtained alloys have body-centred cubic (bcc) crystal structures and form face-centred cubic (fcc) metal hydrides with hydrogen-to-metal ratios close to 2. No correlation between the hydrogen storage capacity and the local lattice strain is observed in this work. Both bcc and fcc unit cells expand linearly with the zirconium-to-metal ratio [Zr]/[M], and increased concentration of Zr stabilizes the hydrides. When heated, the hydrides decompose into the original bcc alloys if [Zr]/[M]<12.5 at.%. The hydrides phase-separate in a hydrogen-induced decomposition type process for [Zr]/[M]≥12.5 at.%. The result is then a combination of two bcc phases, one with a larger and the other with a smaller unit cell than the original bcc alloy.

• El-Kharbachi, Abdelouahab; Sørby, Magnus Helgerud; Nygård, Magnus Moe & Hauback, Bjørn (2019). Borohydride-based Solid-state Electrolytes for Lithium Batteries. In Hibaoui, Abdelaaziz El; Essaaidi, Mohamed & Zaz, Youssef (Ed.), Proceedings of 2019 7th International Renewable and Sustainable Energy Conference (IRSEC). IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781728151526. doi: 10.1109/IRSEC48032.2019.9078280. Full text in Research Archive
• Huot, Jacques; Cuevas, Fermìn; Deledda, Stefano; Edalati, Kaveh; Filinchuk, Yaroslav & Grosdidier, Thierry [Show all 11 contributors for this article] (2019). Mechanochemistry of metal hydrides: Recent advances. Materials. 12:2778(7), p. 1–44. doi: 10.3390/ma12172778. Full text in Research Archive Show summary

  This paper is a collection of selected contributions of the 1st International Workshop on Mechanochemistry of Metal Hydrides that was held in Oslo in May 2018. In this paper, the recent developments in the use of mechanochemistry to synthesize and modify metal hydrides are reviewed. A special emphasis is made on new techniques beside the traditional way of ball milling. High energy milling, ball milling under hydrogen reactive gas, cryomilling and severe plastic deformation techniques such as High-Pressure Torsion (HPT), Surface Mechanical Attrition Treatment (SMAT) and cold rolling are discussed. The new characterization method of in-situ X-ray diffraction during milling is described.

• Pal, Santosh Kumar; Frommen, Christoph; Kumar, Susmit; Hauback, Bjørn; Fjellvåg, Helmer & Woodcock, T. G. [Show all 8 contributors for this article] (2019). Comparative phase transformation and magnetocaloric effect study of Co and Mn substitution by Cu in MnCoGe compounds. Journal of Alloys and Compounds. ISSN 0925-8388. 775, p. 22–29. doi: 10.1016/j.jallcom.2018.10.040. Full text in Research Archive
• Guzik, Matylda N.; Schrade, Matthias; Tofan, Raluca; Carvalho, Patricia Almeida; Berland, Kristian & Sørby, Magnus Helgerud [Show all 9 contributors for this article] (2019). Long- and short-range structures of Ti1-xHfxNi1.0/1.1Sn half-Heusler compounds and their electric transport properties. CrysteEngComm. 21, p. 3330–3342. doi: 10.1039/c9ce00046a. Full text in Research Archive
• Milanese, Chiara; Jensen, Torben René; Hauback, Bjørn; Pistidda, Claudio; Dornheim, Martin & Yang, Heena [Show all 14 contributors for this article] (2019). Complex hydrides for energy storage. International Journal of Hydrogen Energy. ISSN 0360-3199. 14(15), p. 7860–7874. doi: 10.1016/j.ijhydene.2018.11.208. Full text in Research Archive
• Yartys, Volodymyr; Lototskyy, Mykhaylol V.; Akiba, Etsuo; Albert, Rene; Antonov, Vladimir E. & Ares-Fernández, José Ramón [Show all 35 contributors for this article] (2019). Magnesium based materials for hydrogen based energy storage: Past, present and future. International Journal of Hydrogen Energy. ISSN 0360-3199. 44(15), p. 7809–7859. doi: 10.1016/j.ijhydene.2018.12.212. Full text in Research Archive
• Liu, Yinzhe; Heere, Michael; Vasquez, Luis Contreras; Paterakis, Christos; Sørby, Magnus Helgerud & Hauback, Bjørn [Show all 7 contributors for this article] (2018). Dehydrogenation and rehydrogenation of a 0.62LiBH4-0.38NaBH4 mixture with nano-sized Ni. International Journal of Hydrogen Energy. ISSN 0360-3199. 43(34), p. 16782–16792. doi: 10.1016/j.ijhydene.2018.04.211. Full text in Research Archive
• El-Kharbachi, Abdelouahab; Hu, Yang; Sørby, Magnus Helgerud; Mæhlen, Jan Petter; Vullum, Per Erik & Fjellvåg, Helmer [Show all 7 contributors for this article] (2018). Reversibility of metal-hydride anodes in all-solid-state lithium secondary battery operating at room temperature. Solid State Ionics. ISSN 0167-2738. 317, p. 263–267. doi: 10.1016/j.ssi.2018.01.037. Full text in Research Archive Show summary

  The impact on the performance of conversion-type MgH2 anodes by using solid state electrolyte is reported. MgH2 anodes (~26 μm thick) made from homogenous slurries and subsequent drying, are used as model systems along with Li(BH4)0.75I0.25–0.8Li2S·0.2P2S5 as solid electrolyte in an “all-solid-state room-temperature secondary battery”. Electrochemical tests are carried out to investigate cycling properties and elucidate reversibility aspects during the conversion reaction. A major enhancement in performance is observed for the all-solid-state battery compared to MgH2 anodes using carbonate-based liquid electrolytes. This shows that good compatibility and improved reversibility can be obtained for hydride anodes when associated with borohydride-based electrolyte in a Li-ion cell operating at room temperature.

• Guzik, Matylda N.; Echevarria-Bonet, Cristina; Riktor, Marit Dalseth; Carvalho, Patricia Almeida; Gunnæs, Anette Eleonora & Sørby, Magnus Helgerud [Show all 7 contributors for this article] (2018). Half-Heusler phase formation and Ni atom distribution in M-Ni-Sn (M = Hf, Ti, Zr) systems. Acta Materialia. ISSN 1359-6454. 148, p. 216–224. doi: 10.1016/j.actamat.2018.01.019. Full text in Research Archive
• El-Kharbachi, Abdelouahab; Hu, Yang; Yoshida, Koji; Vajeeston, Ponniah; Kim, Sangryun & Sørby, Magnus Helgerud [Show all 9 contributors for this article] (2018). Lithium ionic conduction in composites of Li(BH4)0.75I0.25 and amorphous 0.75Li2S·0.25P2S5 for battery applications. Electrochimica Acta. ISSN 0013-4686. 278, p. 332–339. doi: 10.1016/j.electacta.2018.05.041. Full text in Research Archive
• Qviller, Atle Jorstad; Marstein, Erik Stensrud; You, Chang Chuan; Haug, Halvard; Webster, John R.P. & Hjörvarsson, Björgvin [Show all 8 contributors for this article] (2018). Hydrogen Concentration in Photovoltaic a-Si:H Annealed at Different Temperatures Measured by Neutron Reflectometry. IEEE Journal of Photovoltaics. ISSN 2156-3381. 8(4), p. 1098–1101. doi: 10.1109/JPHOTOV.2018.2838447. Full text in Research Archive
• El-Kharbachi, Abdelouahab; Hu, Yang; Sørby, Magnus Helgerud; Vullum, Per Erik; Mæhlen, Jan Petter & Fjellvåg, Helmer [Show all 7 contributors for this article] (2018). Understanding Capacity Fading of MgH2 Conversion-Type Anodes via Structural Morphology Changes and Electrochemical Impedance. Journal of Physical Chemistry C. ISSN 1932-7447. 122(16), p. 8750–8759. doi: 10.1021/acs.jpcc.7b12656. Full text in Research Archive Show summary

  Previous studies have demonstrated that MgH2 is a promising conversion-type anode toward Li with high capacity (2037 mAh/g) and low discharge/charge overpotential hysteresis. A major challenge is the capacity loss after a few cycles. To improve the understanding of the complex conversion mechanism at the electrode/electrolyte interface and of its possible evolution, a systematic investigation of the morphology–property relation is undertaken. A multitude of MgH2 materials are obtained by mechanical milling using different devices, milling conditions, and time intervals. Upon cycling, the performance of the assembled batteries is strongly dependent on the quality of the prepared MgH2 powders. Electrochemical discharge/charge profiles (MgH2 ⇆ 2LiH + Mg) are discussed according to the changes in microstructure and morphology revealed by powder X-ray diffraction and transmission electron microscopy. For all electrode composites, the loss of the capacity occurs typically during delithiation in agreement with a kinetically limited process, namely, of LiH “detachment”. Electrochemical impedance spectroscopy is meaningfully carried out using the representative tape-casted electrodes in Li/MgH2 cells to monitor the evolution of resistance components, in particular the formation of a solid electrolyte interphase (SEI)-like layer as a function of particle size, state of charge, and cycle number.

• Sartori, Sabrina; Guzik, Matylda N.; Knudsen, Kenneth Dahl; Sørby, Magnus Helgerud; Jr., Joseph A. Teprovich, & Zidan, Ragaiy [Show all 7 contributors for this article] (2018). Stability and Phase Formation in the (Li/Na)6C60–H Systems Studied by Neutron Scattering. Journal of Physical Chemistry C. ISSN 1932-7447. 122(32), p. 18346–18355. doi: 10.1021/acs.jpcc.8b05977. Full text in Research Archive Show summary

  Small-angle neutron scattering combined with powder neutron diffraction was employed to study the phase formation upon absorption/desorption of hydrogen gas in Li- and Na-intercalated fullerides. The comparative system analysis, addressing changes in the sample phase compositions and the morphology of powders, revealed a higher degree of complexity in the Na-based samples. Results also showed that the disappearance of crystalline lithium/sodium hydride during desorption was accompanied by an increased surface roughness in both systems, most likely because of the formation of a local surface strain. Furthermore, an increased specific internal surface of the studied materials upon subsequent deuterium absorption/desorption cycles was demonstrated. This could indicate moderate fracturing of crystallites.

• Weidenthaler, Claudia; Felderhoff, Michael; Bernert, Thomas; Sørby, Magnus Helgerud; Hauback, Bjørn & Krech, Daniel (2018). Synthesis, Crystal Structure Analysis and Decomposition of RbAlH4. Crystals. 8(2). doi: 10.3390/cryst8020103. Full text in Research Archive
• Sato, Toyoto; Takagi, Shigeyuki; Sørby, Magnus Helgerud; Deledda, Stefano; Hauback, Bjørn & Orimo, Shin-ichi (2018). Crystal Structural Determination of SrAlD5 with Corner-Sharing AlD6 Octahedron Chains by X-ray and Neutron Diffraction. Crystals. 8(2), p. 89–89. doi: 10.3390/cryst8020089. Full text in Research Archive
• Santoru, Antonio; Pistidda, Claudio; Brighi, Matteo; Chierotti, Michele R.; Heere, Michael & Karimi, Fahim [Show all 16 contributors for this article] (2018). Insights into the Rb–Mg–N–H System: an Ordered Mixed Amide/Imide Phase and a Disordered Amide/Hydride Solid Solution. Inorganic Chemistry. ISSN 0020-1669. 57(6), p. 3197–3205. doi: 10.1021/acs.inorgchem.7b03232. Full text in Research Archive
• El-Kharbachi, Abdelouahab; Uesato, Hiroki; Kawai, Hironori; Wenner, Sigurd; Miyaoka, Hiroki & Sørby, Magnus Helgerud [Show all 9 contributors for this article] (2018). MgH2–CoO: a conversion-type composite electrode for LiBH4-based all-solid-state lithium ion batteries. RSC Advances. 8(41), p. 23468–23474. doi: 10.1039/c8ra03340d. Full text in Research Archive Show summary

  Several studies have demonstrated that MgH2 is a promising conversion-type anode toward Li. A major obstacle is the reversible capacity during cycling. Electrochemical co-existence of a mixed metal hydride-oxide conversion type anode is demonstrated for lithium ion batteries using a solid-state electrolyte. 75MgH2$25CoO anodes are obtained from optimized mixing conditions avoiding reactions occurring during high-energy ball-milling. Electrochemical tests are carried out to investigate the cycling capability and reversibility of the on-going conversion reactions. The cycling led to formation of a singleplateau nanocomposite electrode with higher reversibility yield, lowered discharge–charge hysteresis and mitigated kinetic effect at high C-rate compared to MgH2 anodes. It is believed that reduced diffusion pathways and less polarized electrodes are the origin of the improved properties. The designed composite-electrode shows good preservation and suitability with LiBH4 solid electrolyte as revealed from electron microscopy analyses and X-ray photoelectron spectroscopy.

• Heere, Michael; Zavorotynska, Olena; Deledda, Stefano; Sørby, Magnus Helgerud; Book, David & Steriotis, Theodore [Show all 7 contributors for this article] (2018). Effect of additives, ball milling and isotopic exchange in porous magnesium borohydride. RSC Advances. 8(49), p. 27645–27653. doi: 10.1039/C8RA05146A. Full text in Research Archive Show summary

  Magnesium borohydride (Mg(BH4)2) is a promising material for solid state hydrogen storage. However, the predicted reversible hydrogen sorption properties at moderate temperatures have not been reached due to sluggish hydrogen sorption kinetics. Hydrogen (H) → deuterium (D) exchange experiments can contribute to the understanding of the stability of the BH4− anion. Pure γ-Mg(BH4)2, ball milled Mg(BH4)2 and composites with the additives nickel triboride (Ni3B) and diniobium pentaoxide (Nb2O5) have been investigated. In situ Raman analysis demonstrated that in pure γ-Mg(BH4)2 the isotopic exchange reaction during continuous heating started at ∼80 °C, while the ball milled sample did not show any exchange at 3 bar D2. However, during ex situ exchange reactions investigated by infrared (IR) and thermogravimetric (TG) analyses a comparable H → D exchange during long exposures (23 h) to deuterium atmosphere was observed for as received, ball milled and γ-Mg(BH4)2 + Nb2O5, while the Ni3B additive hindered isotopic exchange. The specific surface areas (SSA) were shown to be very different for as received γ-Mg(BH4)2, BET area = 900 m2 g−1, and ball milled Mg(BH4)2, BET area = 30 m2 g−1, respectively, and this explains why no gas–solid H(D) diffusion was observed for the ball milled (amorphous) Mg(BH4)2 during the short time frames of in situ Raman measurements. The heat treated ball milled sample partially regained the porous γ-Mg(BH4)2 structure (BET area = 560 m2 g−1). This in combination with the long reaction times allowing for the reaction to approach equilibrium explains the observed gas–solid H(D) diffusion during long exposure. We have also demonstrated that a small amount of D can be substituted in both high surface area and low surface area samples at room temperature proving that the B–H bonds in Mg(BH4)2 can be challenged at these mild conditions.

• Gharibdoust, SevedHosein Payandeh; Heere, Michael; Nervi, Carlo; Sørby, Magnus Helgerud; Hauback, Bjørn & Jensen, Torben R. (2018). Synthesis, structure, and polymorphic transitions of praseodymium(III) and neodymium(III) borohydride, Pr(BH4)3 and Nd(BH4)3. Dalton Transactions. ISSN 1477-9226. 47(25), p. 8307–8319. doi: 10.1039/c8dt00118a. Full text in Research Archive
• Frommen, Christoph; Sørby, Magnus Helgerud; Heere, Michael; Humphries, Terry David; Olsen, Jørn Erik & Hauback, Bjørn (2017). Rare earth borohydrides - Crystal structures and thermal properties. Energies. 10(12). doi: 10.3390/en10122115. Full text in Research Archive
• Floriano, R.; Deledda, Stefano; Hauback, Bjørn; Leiva, Daniel Rodrigo & Botta, W.J. (2017). Iron and niobium based additives in magnesium hydride: Microstructure and hydrogen storage properties. International Journal of Hydrogen Energy. ISSN 0360-3199. 42(10), p. 6810–6819. doi: 10.1016/j.ijhydene.2016.11.117. Full text in Research Archive
• Sato, Toyoto; Ikeda, Kazutaka; Matsuo, Motoaki; Miwa, Kazutoshi; Otomo, Toshiya & Deledda, Stefano [Show all 10 contributors for this article] (2017). In-situ powder neutron diffraction study on the formation process of LaMg2NiH7. International Journal of Hydrogen Energy. ISSN 0360-3199. 42(35), p. 22449–22453. doi: 10.1016/j.ijhydene.2017.02.196. Full text in Research Archive
• El-Kharbachi, Abdelouahab; Andersen, Hanne Flåten; Sørby, Magnus Helgerud; Vullum, Per Erik; Mæhlen, Jan Petter & Hauback, Bjørn (2017). Morphology effects in MgH2 anode for lithium ion batteries. International Journal of Hydrogen Energy. ISSN 0360-3199. 42(35), p. 22551–22556. doi: 10.1016/j.ijhydene.2017.04.298. Full text in Research Archive Show summary

  In order to acquire reproducible electrodes relevant for Li ion batteries new MgH2 electrodes are successfully obtained from homogenous slurries in N-Methyl-2-Pyrrolidone “NMP” solvent. The electrodes are aimed to elucidate the contribution of the cell components to the electrochemical cycling, in terms of morphology and composition. Various electrode preparations were tested and compared regarding their interaction with Li in a half-cell. The obtained electrochemical cycling curves are discussed according to the ball-milling-induced structural morphology changes and presence of carbon additives, along with the effect of the kinetic rate on the conversion reaction mechanism.

• Guzik, Matylda Natalia; Golasinski, Karol M.; Pedrosa, F.J.; Jenus, Petra; Bollero, Alberto & Hauback, Bjørn [Show all 7 contributors for this article] (2017). Influence of ultra-short cryomilling on the microstructural and magnetic properties of cobalt ferrite. Journal of Alloys and Compounds. ISSN 0925-8388. 721, p. 440–448. doi: 10.1016/j.jallcom.2017.05.290. Full text in Research Archive

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• Kosler, Josef; Sjåstad, Anja Olafsen; Fjellvåg, Øystein Slagtern; Frommen, Christoph & Hauback, Bjørn Christian (2026). Study of Magnetic and Structural Properties of Ho1-xNdxVO3 for Hydrogen Liquefaction. Full text in Research Archive
• Kumar, Abhishek; Fjellvåg, Helmer; Deledda, Stefano; Hauback, Bjørn Christian & Sjåstad, Anja Olafsen (2026). Composition-Tuned Phase Evolution in BCC (TiVZrNb)1-xMx HEAs (M = Ni, Fe, Mn, Co, Cr). Full text in Research Archive
• Lunde, Vilde Sturtzel; Møller, Amalie Bisgaard; Eggert, Bruno Guilherme Fischer; Döring, Allan; Grivel, Jean-Claude & Bjørk, Rasmus [Show all 12 contributors for this article] (2025). Machine Learning Guided Discovery of Light Rare Earth Laves Phases for Magnetocaloric Hydrogen Liquefaction. Full text in Research Archive
• Lunde, Vilde Sturtzel; Møller, Amalie Bisgaard; Eggert, Bruno Guilherme Fischer; Döring, Allan; Straßheim, Marc & Grivel, Jean-Claude [Show all 15 contributors for this article] (2025). Machine Learning Guided Discovery Light Rare Earth Laves Phases for Magnetocaloric Hydrogen Liquefaction. Full text in Research Archive
• Lunde, Vilde Sturtzel; Fjellvåg, Øystein Slagtern; Pomjakushin, Vladimir; Sjåstad, Anja Olafsen; Hauback, Bjørn Christian & Frommen, Christoph (2025). Influence of Ni-Substitution on Structural and Magnetic Transitions of NdCo2. Full text in Research Archive
• Roggio, Alice; Eggert, Bruno Guilherme Fischer; Mulas, Gabriele; Hauback, Bjørn Christian & Deledda, Stefano (2025). Exploring the Mechanochemical Reduction of Ilmenite for the production of TiFe Hydrogen Storage Alloys. Full text in Research Archive Show summary

  TiFeHx has recently emerged as a realistic candidate for solid-state hydrogen storage applications.1 Partial substitution of Fe with other transition metals (e.g. Ni, Cu, Mn) allows a reversible hydrogen absorption and desorption at moderate conditions and good sorption kinetics. The volumetric hydrogen storage capacity for TiFe can be as high as 110 kgH2/m3 (3.7 MWh/m3), which is significantly higher than that for liquid hydrogen. Besides the technological benefits, one of the main advantages of the TiFe system is cost. Fe and Ti are relatively cheap and abundant raw materials which are easily recyclable. However, in October 2020, titanium was included in the list of critical raw materials by the EU, due to its economic importance and to an increased supply risk. Nonetheless, Norway has large resources of titanium ores in the form of ilmenite, FeTiO3, estimated to about 5% of the World’s total reserves. Ilmenite may clearly be an ideal starting point for production of TiFe as it contains the two metallic constituents in the correct stochiometric ratio. In this work, the production of TiFe from Norwegian ilmenite via mechanochemical methods is explored. In particular, high energy ball milling is used to promote the mechanochemical reduction of ilmenite by alkaline earth hydrides. Results from Powder X-ray Diffraction (PXD) analysis and Scanning Electron Microscopy (SEM) show that the reduction of ilmenite can be partially achieved depending on the ball milling technique and reducing agent employed during processing. In particular, it is shown that the amount of FeTiO3 phase decreases as a function of milling time, suggesting a gradual conversion of ilmenite to a Fe/Ti cubic phase. The results are discussed with respect to the milling conditions chosen for this work, such as milling atmosphere and milling intensity. Additionally, the purity of the starting ilmenite ore is considered for the evaluating the phase distribution in the final powders after the milling process and for assessing the potential of the mechanochemical reduction products for hydrogen storage applications. This work was supported by the Research Council of Norway through the Norwegian Centre for Hydrogen and Ammonia Research HYDROGENi [Grant No. 333118].

• Hauback, Bjørn Christian (2025). Reversible NaAlH4 with titanium-based additives - what have we learned about the mechanism? Full text in Research Archive
• Lunde, Vilde Sturtzel; Fjellvåg, Øystein Slagtern; Frommen, Christoph; Sjåstad, Anja Olafsen & Hauback, Bjørn Christian (2025). Influence of Ni-Substitution on Structural and Magnetic Transitions of NdCo2. Full text in Research Archive
• Silva, Valmir Rodrigo da; Hauback, Bjørn Christian & Deledda, Stefano (2024). Exploring the Formation of Ordered Tetrataenite Phase in Cryomilled FeNi Alloys with Small Carbon Additions. Full text in Research Archive
• Eggert, Bruno Guilherme Fischer; Hauback, Bjørn Christian & Deledda, Stefano (2024). PREPARATION OF TiFe FROM ILMENITE, FeTiO3, FOR HYDROGEN STORAGE. Full text in Research Archive
• Eggert, Bruno Guilherme Fischer; Döring, Allan; Skokov, K.P.; Gutfleisch, Oliver; Hauback, Bjørn Christian & Frommen, Christoph (2024). Structure-property relationships in GdCuX corresponding hydrides (X= Si, Al). Full text in Research Archive
• Frommen, Christoph; Knudsen, Kenneth Dahl; Hauback, Bjørn Christian & Røhme, Camilla (2023). Skal gjøre hydrogenproduksjon billigere - med magneter. [Journal]. Teknisk Ukeblad. Full text in Research Archive
• Silva, Valmir Rodrigo da; Deledda, Stefano & Hauback, Bjørn Christian (2023). The possible formation of tetrataenite by mechanical activation and the addition of light elements. Full text in Research Archive
• Eggert, Bruno Guilherme Fischer; Hauback, Bjørn Christian & Frommen, Christoph (2023). Inexpensive materials for magnetic cooling. Full text in Research Archive
• Silva, Valmir Rodrigo da; Deledda, Stefano & Hauback, Bjørn Christian (2023). Developing permanent magnets inspired by meteorites. Full text in Research Archive
• Fjellvåg, Øystein; Sønsteby, Henrik Hovde; Nilsen, Ola; Wolff, Max; Kapaklis, Vassilios & Fjellvåg, Helmer [Show all 8 contributors for this article] (2020). Towards Multiferroic Thin Film Composites by Atomic Layer Deposition (ALD). Full text in Research Archive
• Zavorotynska, Olena; Deledda, Stefano; Orimo, Shin-ichi; Matsuo, Motoaki & Hauback, Bjørn (2019). In-situ Raman Study of H → D Exchange in γ-Mg(BH4)2. Full text in Research Archive
• Nygård, Magnus Moe; Ek, Gustav; Keen, David A.; Ikeda, Kazutaka; Sakaki, Kouji & Karlsson, Dennis [Show all 9 contributors for this article] (2019). A mechanistic explanation of the destabilization mechanism in metal hydrides formed from high-entropy alloys. Full text in Research Archive
• Nygård, Magnus Moe; Ek, Gustav; Keen, David A.; Ikeda, Kazutaka; Karlsson, Dennis & Sørby, Magnus Helgerud [Show all 8 contributors for this article] (2019). A mechanistic explanation of the destabilization mechanism in metal hydrides formed from high-entropy alloys. Full text in Research Archive
• Nygård, Magnus Moe; Ek, Gustav; Sahlberg, Martin; Sørby, Magnus Helgerud & Hauback, Bjørn Christian (2018). Hydrogen storage in high-entropy alloys with varying degree of local lattice strain. Full text in Research Archive
• Nygård, Magnus Moe; Ek, Gustav; Sørby, Magnus Helgerud; Sahlberg, Martin & Hauback, Bjørn Christian (2018). A roadmap towards reversible room-temperature hydrogen storage in high-entropy alloys. Full text in Research Archive
• El-Kharbachi, Abdelouahab; Høgset, A.; Kim, Sangryun; Vajeeston, Ponniah; Sørby, Magnus Helgerud & Fjellvåg, Helmer [Show all 8 contributors for this article] (2018). Structural and Electrochemical Study of Mixtures of Halogenated-LiBH4 and Amorphous 0.75Li2S·0.25P2S5 for Li- Conducting Solid Electrolytes. Full text in Research Archive
• Guzik, Matylda N.; Echevarria-Bonet, Cristina; Sørby, Magnus Helgerud & Hauback, Bjørn (2017). Half-Heusler Phase Formation and Ni atom distribution in M-Ni-Sn (M = Hf, Ti, Zr) System. Full text in Research Archive
• Guzik, Matylda N.; Schrade, Matthias; Tofan, Raluca; Berland, Kristian; Gunnæs, Anette Eleonora & Persson, Clas [Show all 8 contributors for this article] (2017). Structural Investigation of Ti1-xHfxNiySn Half-Heusler Compounds. Full text in Research Archive
• El-Kharbachi, Abdelouahab; Hu, Yang; Yoshida, Koji; Sørby, Magnus Helgerud; Fjellvåg, Helmer & Orimo, Shin-Ichi [Show all 7 contributors for this article] (2017). Ionic Properties of the Li(BH4)0.75I0.25 - 0.75Li2S·0.25P2S5 Mixed System for Near Room-Temperature All-Solid Li-Ion Batteries. Full text in Research Archive
• El-Kharbachi, Abdelouahab; Hu, Yang; Yoshida, Koji; Sørby, Magnus Helgerud; Ichikawa, Takayuki & Fjellvåg, Helmer [Show all 8 contributors for this article] (2017). Hydride materials in all-solid Li-ion cell configuration for room and high temperature applications. Full text in Research Archive
• Lunde, Vilde Sturtzel; Hauback, Bjørn Christian; Sjåstad, Anja Olafsen & Frommen, Christoph (2026). Light Rare-Earth Based Laves Phases for Magnetocaloric Hydrogen Liquefaction. Universitetet i Oslo. Full text in Research Archive Show summary

  Given the pressing issue of climate change, there is a need to transition to more sustainable and lower-emission technologies. Hydrogen is a renewable energy carrier, but suffers from low volumetric energy density, which makes it challenging to store and transport. Cooling hydrogen from gas to liquid greatly reduces its volume, but current liquefaction technologies are highly energy-intensive and expensive as one approach the liquefaction point of hydrogen (20 K or -253 °C). Magnetic cooling utilizes the magnetocaloric effect of magnetic materials and offers a potentially more efficient alternative. The currently known most efficient magnetocaloric materials rely on expensive and scarce heavy rare-earth elements. Therefore, this work studies the effects of substituting these with light rare-earth elements. Machine learning models trained on compounds reported in the literature were successfully used to screen light rare-earth based compounds. Promising candidates were experimentally synthesized and characterized to examine their magnetocaloric effect. Furthermore, advanced characterization techniques including neutron scattering and synchrotron-based techniques were used to understand the materials and how to optimize them for magnetic refrigeration applications.

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