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Hydrogen is an efficient energy carrier that can be produced from renewable sources, enabling the transition towards CO 2 -free energy. Hydrogen can be stored for a long period in the solid-state, with suitable alloys. Ti-rich TiFe 0.90 compound exhibits a mild activation process for the first hydrogenation, and Ti(Fe,Mn) 0.90 substituted alloys can lead to the fine tuning of equilibrium pressure as a function of the final application. In this study, the crystal structure of TiFe (0.90- x) Mn x alloys (x = 0, 0.05 and 0.10) and their deuterides has been determined by in-situ neutron diffraction, while recording Pressure-Composition Isotherms at room temperature. The investigation aims at analysing the influence of Mn for Fe substitution in Ti-rich Ti(Fe,Mn) 0.90 alloys on structural properties during reversible deuterium loading, which is still unsolved and seldom explored. After activation, samples have been transferred into custom-made stainless-steel and aluminium alloy cells used for in-situ neutron diffraction experiments during deuterium loading at ILL and ISIS neutron facilities, respectively. The study enables remarkable understanding on hydrogen storage, basic structural knowledge, and support to the industrial application of TiFe-type alloys for integrated hydrogen tank in energy storage systems by determining the volume expansion during deuteration. Furthermore, the study demonstrates that different contents of Mn do not significantly change the volumetric expansion during phase transitions, affecting only the deuterium content for the γ phase and the cell evolution for the β phase. The study confirms that the deuterated structures of the γ phase upon absorption, β and α phase upon desorption, correspond to S.G. Cmmm , P 222 1 and Pm -3 m , respectively. [Display omitted] • Effect of Mn content on structural and hydrogenation properties in TiFe determined. • Mn-substituted TiFe deuterates structures determined by in situ neutron diffraction. • Mn does not significantly change volumetric expansion during phase transitions. • Mn substitution affects deuterium content for γ and cell evolution for β phase. • Mn substitution favours a stable deuterium occupancy over 2 a and 2 d sites. [ABSTRACT FROM AUTHOR]

Hydrogen is an efficient energy carrier that can be produced from renewable sources, enabling the transition towards CO 2 -free energy. Hydrogen can be stored for a long period in the solid-state, with suitable alloys. Ti-rich TiFe 0.90 compound exhibits a mild activation process for the first hydrogenation, and Ti(Fe,Mn) 0.90 substituted alloys can lead to the fine tuning of equilibrium pressure as a function of the final application. In this study, the crystal structure of TiFe (0.90- x) Mn x alloys (x = 0, 0.05 and 0.10) and their deuterides has been determined by in-situ neutron diffraction, while recording Pressure-Composition Isotherms at room temperature. The investigation aims at analysing the influence of Mn for Fe substitution in Ti-rich Ti(Fe,Mn) 0.90 alloys on structural properties during reversible deuterium loading, which is still unsolved and seldom explored. After activation, samples have been transferred into custom-made stainless-steel and aluminium alloy cells used for in-situ neutron diffraction experiments during deuterium loading at ILL and ISIS neutron facilities, respectively. The study enables remarkable understanding on hydrogen storage, basic structural knowledge, and support to the industrial application of TiFe-type alloys for integrated hydrogen tank in energy storage systems by determining the volume expansion during deuteration. Furthermore, the study demonstrates that different contents of Mn do not significantly change the volumetric expansion during phase transitions, affecting only the deuterium content for the γ phase and the cell evolution for the β phase. The study confirms that the deuterated structures of the γ phase upon absorption, β and α phase upon desorption, correspond to S.G. Cmmm , P 222 1 and Pm -3 m , respectively. [Display omitted] • Effect of Mn content on structural and hydrogenation properties in TiFe determined. • Mn-substituted TiFe deuterates structures determined by in situ neutron diffraction. • Mn does not significantly change volumetric expansion during phase transitions. • Mn substitution affects deuterium content for γ and cell evolution for β phase. • Mn substitution favours a stable deuterium occupancy over 2 a and 2 d sites. [ABSTRACT FROM AUTHOR]

Abstract: On the basis of a previously acquired experience on scaling up issues concerning the use of magnesium hydride as a base material for solid-state hydrogen storage, a small reactor was designed and tested in different operating conditions. It contains about 10g of catalyzed magnesium hydride powder mixed with 5wt.% aluminium powder and pressed in the form of cylindrical pellets and the heat flow is managed by means of an oil circulation system. Carbon paper is used to ensure good heat conductivity between the pellets and the inner wall of the reactor and between one pellet and another. A number of hydrogen absorption and desorption cycles at different temperatures and pressures was carried out to compare the behaviour of the small reactor with the laboratory data obtained on small amounts (fractions of grams) of powdered and pelletized samples. Data acquisition for gas flow, pressure and temperature in different positions of the reactor allow a good understanding of internal dynamics. The results in terms of hydrogen absorption/desorption kinetics and of stability to ongoing cycles are stimulating, so that the tested small reactor can be considered as a basic element for further studies and improvements. [Copyright &y& Elsevier]

This work proposes an effective thermal activation method with low technical effort for industrially produced titanium-iron-manganese powders (TiFeMn) for hydrogen storage. In this context, the influence of temperature and particle size of TiFeMn on the activation process is systematically studied. The results obtained from this investigation suggest that the activation of the TiFeMn material at temperatures as low as 50 °C is already possible, with a combination of "Dynamic" and "Static" routines, and that an increase to 90 °C strongly reduces the incubation time for activation, i.e. the incubation time of the sample with the two routines at 90 °C is about 0.84 h, while ∼ 277 h is required for the sample treated at 50 °C in both "Dynamic" and "Static" sequences. Selecting TiFeMn particles of larger size also leads to significant improvements in the activation performance of the investigated material. The proposed activation routine makes it possible to overcome the oxide layer existing on the compound surface, which acts as a diffusion barrier for the hydrogen atoms. This activation method induces further cracks and defects in the powder granules, generating new surfaces for hydrogen absorption with greater frequency, and thus leading to faster sorption kinetics in the subsequent absorption-desorption cycles. [Display omitted] • An effective, low technical effort, thermal activation method for TiFe alloy is proposed. • Systematic analysis of the effect of temperature and particle size on the activation. • The diffusion barrier, due to the oxide layer on the surface, is overcome. • Creation of cracks and defects in the powder leads to improved initial kinetics. [ABSTRACT FROM AUTHOR]

• Dependency of hydrogenation properties over extended Ti and Mn compositional range. • Ti and Mn substitutions enlarge TiFe cell volume and linearly reduce equilibrium pressure and hysteresis. • Samples at the Ti-rich side have enhanced storage reversible capacities. • Formation of secondary phases allows first hydrogenation in milder conditions. • Sample s6: best compositional trade-off (high capacity, 1.63 wt%, easy activation, good kinetics). [Display omitted] TiFe intermetallic compound has been extensively studied, owing to its low cost, good volumetric hydrogen density, and easy tailoring of hydrogenation thermodynamics by elemental substitution. All these positive aspects make this material promising for large-scale applications of solid-state hydrogen storage. On the other hand, activation and kinetic issues should be amended and the role of elemental substitution should be further understood. This work investigates the thermodynamic changes induced by the variation of Ti content along the homogeneity range of the TiFe phase (Ti:Fe ratio from 1:1–1:0.9) and of the substitution of Mn for Fe between 0 and 5 at%. In all considered alloys, the major phase is TiFe-type together with minor amounts of TiFe 2 or β-Ti-type and Ti 4 Fe 2 O-type at the Ti-poor and rich side of the TiFe phase domain, respectively. Thermodynamic data agree with the available literature but offer here a comprehensive picture of hydrogenation properties over an extended Ti and Mn compositional range. Moreover, it is demonstrated that Ti-rich alloys display enhanced storage capacities, as long as a limited amount of β-Ti is formed. Both Mn and Ti substitutions increase the cell parameter by possibly substituting Fe, lowering the plateau pressures and decreasing the hysteresis of the isotherms. A full picture of the dependence of hydrogen storage properties as a function of the composition will be discussed, together with some observed correlations. [ABSTRACT FROM AUTHOR]