Synthesis and characterization of Magnesium-Iron-Cobalt complex hydrides

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TiFe0.85Mn0.05 alloy produced at industrial level for a hydrogen storage plant

Moving from basic research to the implementation of hydrogen storage system based on metal hydride, the industrial production of the active material is fundamental. The alloy TiFe0.85Mn0.05 was selected as H2-carrier for a storage plant of about 50 kg of H2. In this work, a batch of 5 kg of TiFe0.85Mn0.05 alloy was synthesized at industrial level and characterized to determine the structure and phase abundance. The H2 sorption properties were investigated, performing studies on long-term cycling study and resistance to poisoning. The alloy absorbs and desorbs hydrogen between 25 bar and 1 bar at 55 °C, storing 1.0 H2 wt.%, displaying fast kinetic, good resistance to gas impurities, and storage stability over 250 cycles. The industrial production promotes the formation of a passive layer and a high amount of secondary phases, observing differences in the H2 sorption behaviour compared to samples prepared at laboratory scale. This work highlights how hydrogen sorption properties of metal hydrides are strictly related to the synthesis method

Reactive Hydride Composite of Mg2NiH4 with Borohydrides Eutectic Mixtures

The development of materials showing hydrogen sorption reactions close to room temperature and ambient pressure will promote the use of hydrogen as energy carrier for mobile and stationary large-scale applications. In the present study, in order to reduce the thermodynamic stability of MgH2, Ni has been added to form Mg2NiH4, which has been mixed with various borohydrides to further tune hydrogen release reactions. De-hydrogenation/re-hydrogenation properties of Mg2NiH4-LiBH4-M(BH4)(x) (M = Na, K, Mg, Ca) systems have been investigated. Mixtures of borohydrides have been selected to form eutectics, which provide a liquid phase at low temperatures, from 110 degrees C up to 216 degrees C. The presence of a liquid borohydride phase decreases the temperature of hydrogen release of Mg2NiH4 but only slight differences have been detected by changing the borohydrides in the eutectic mixture

Reactive Hydride Composite of Mg2NiH4 with Borohydrides Eutectic Mixtures

International audienceThe development of materials showing hydrogen sorption reactions close to room temperature and ambient pressure will promote the use of hydrogen as energy carrier for mobile and stationary large-scale applications. In the present study, in order to reduce the thermodynamic stability of MgH2, Ni has been added to form Mg2NiH4, which has been mixed with various borohydrides to further tune hydrogen release reactions. De-hydrogenation/re-hydrogenation properties of Mg2NiH4-LiBH4-M(BH4)(x) (M = Na, K, Mg, Ca) systems have been investigated. Mixtures of borohydrides have been selected to form eutectics, which provide a liquid phase at low temperatures, from 110 degrees C up to 216 degrees C. The presence of a liquid borohydride phase decreases the temperature of hydrogen release of Mg2NiH4 but only slight differences have been detected by changing the borohydrides in the eutectic mixture

Phase diagrams of the LiBH4-NaBH4-KBH4 system

A combination of experimental and computational techniques has been used to fully describe the thermodynamic properties and phase diagrams of the LiBH4-NaBH4-KBH4 system. The Calphad method was used to assess the thermodynamic properties of LiBH4-NaBH4, LiBH4-KBH4, and NaBH4-KBH4 binary systems and to extend the investigation to the LiBH4-NaBH4-KBH4 ternary system. Samples with various compositions in the ternary system were synthesised, both by ball milling and manual mixing of the parent borohydrides, and their thermal stability has been studied using in situ synchrotron radiation X-ray diffraction as a function of temperature and using differential scanning calorimetry. From collected experimental and literature data, a thermodynamic assessment of the ternary system led to the determination of the phase diagrams. In all cases, the solid solutions can be described in the frame of the regular solution model, with interaction parameters positive or equal to zero (i.e. ideal solution). In contrast, the liquid phase was described using negative interaction parameters. A new ternary eutectic composition was estimated and it was confirmed experimentally to be equal to a molar fraction of 0.66LiBH(4)-0.11NaBH(4)-0.23KBH(4) with a melting temperature of 102 degrees C

A thermodynamic investigation of the LiBH4-NaBH4 system

The LiBH4\u2013NaBH4 pseudo-binary system has been investigated by X-ray diffraction, temperature-programmed photographic analysis, and differential scanning calorimetry, in order to establish the phase diagram. The polymorphic orthorhombic-to-hexagonal phase transition of LiBH4 was observed at 94 \ub0C in samples containing NaBH4, i.e. 15 \ub0C lower than for pure LiBH4, which indicates the dissolution of sodium into LiBH4. The formation of solid solutions was confirmed by powder X-ray diffraction measurements performed as a function of temperature. A new eutectic composition between Li0.65Na0.35BH4 and Li0.70Na0.30BH4, with a melting temperature of 216 \ub0C, is observed. Ab initio calculations have been performed to establish the relative stabilities of the pure compounds in orthorhombic, hexagonal and cubic structures. The obtained experimental and calculated data were compared with available literature values and they were used for a thermodynamic assessment of the LiBH4\u2013NaBH4 system by the calphad method. The enthalpy of mixing for solid and liquid solutions has been estimated on the basis of experimental data