Design of a Nanometric AlTi Additive for MgB2-Based Reactive Hydride Composites with Superior Kinetic Properties

Solid-state hydride compounds are a promising option for efficient and safe hydrogen-storage systems. Lithium reactive hydride composite system 2LiBH4 + MgH2/2LiH + MgB2 (Li-RHC) has been widely investigated owing to its high theoretical hydrogen-storage capacity and low calculated reaction enthalpy (11.5 wt % H2 and 45.9 kJ/mol H2). In this paper, a thorough investigation into the effect of the formation of nano-TiAl alloys on the hydrogen-storage properties of Li-RHC is presented. The additive 3TiCl3·AlCl3 is used as the nanoparticle precursor. For the investigated temperatures and hydrogen pressures, the addition of ∼5 wt % 3TiCl3·AlCl3 leads to hydrogenation/dehydrogenation times of only 30 min and a reversible hydrogen-storage capacity of 9.5 wt %. The material containing 3TiCl3·AlCl3 possesses superior hydrogen-storage properties in terms of rates and a stable hydrogen capacity during several hydrogenation/dehydrogenation cycles. These enhancements are attributed to an in situ nanostructure and a hexagonal AlTi3 phase observed by high-resolution transmission electron microscopy. This phase acts in a 2-fold manner, first promoting the nucleation of MgB2 upon dehydrogenation and second suppressing the formation of Li2B12H12 upon hydrogenation/dehydrogenation cycling.Fil: Le, Thi-Thu. Helmholtz Zentrum Geesthacht; AlemaniaFil: Pistidda, Claudio. Helmholtz Zentrum Geesthacht; AlemaniaFil: Puszkiel, Julián Atilio. Helmholtz Zentrum Geesthacht; Alemania. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Castro Riglos, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Helmholtz Zentrum Geesthacht; Alemania. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Karimi, Fahim. Helmholtz Zentrum Geesthacht; AlemaniaFil: Skibsted, Jørgen. University Aarhus; DinamarcaFil: Gharibdoust, Seyedhosein Payandeh. University Aarhus; DinamarcaFil: Richter, Bo. University Aarhus; DinamarcaFil: Emmler, Thomas. Helmholtz Zentrum Geesthacht; AlemaniaFil: Milanese, Chiara. Università di Pavia; ItaliaFil: Santoru, Antonio. Helmholtz Zentrum Geesthacht; AlemaniaFil: Hoell, Armin. Helmholtz Zentrum Berlin für Materialien und Energie; AlemaniaFil: Krumrey, Michael. Physikalisch Technische Bundesanstalt; AlemaniaFil: Gericke, Eike. Universität zu Berlin; AlemaniaFil: Akiba, Etsuo. Kyushu University; JapónFil: Jensen, Torben R.. University Aarhus; DinamarcaFil: Klassen, Thomas. Helmholtz Zentrum Geesthacht; Alemania. Helmut Schmidt University; AlemaniaFil: Dornheim, Martin. Helmholtz Zentrum Geesthacht; Alemani

Synthesis, structure and properties of bimetallic sodium rare-earth (RE) borohydrides, NaRE(BH₄)₄,RE = Ce, Pr, Er or Gd

Formation, stability and properties of new metal borohydrides within RE(BH4)3–NaBH4, RE = Ce, Pr, Er or Gd is investigated. Three new bimetallic sodium rare-earth borohydrides, NaCe(BH4)4, NaPr(BH4)4 and NaEr(BH4)4 are formed based on an addition reaction between NaBH4 and halide free rare-earth metal borohydrides RE(BH4)3, RE = Ce, Pr, Er. All the new compounds crystallize in the orthorhombic crystal system. NaCe(BH4)4 has unit cell parameters of a = 6.8028(5), b = 17.5181(13), c = 7.2841(5) Å and space group Pbcn. NaPr(BH4)4 is isostructural to NaCe(BH4)4 with unit cell parameters of a = 6.7617(2), b = 17.4678(7), c = 7.2522(3) Å. NaEr(BH4)4 crystallizes in space group Cmcm with unit cell parameters of a = 8.5379(2), b = 12.1570(4), c = 9.1652(3) Å. The structural relationships, also to the known RE(BH4)3, are discussed in detail and related to the stability and synthesis conditions. Heat treatment of NaBH4–Gd(BH4)3 mixture forms an unstable amorphous phase, which decomposes after one day at RT. NaCe(BH4)4 and NaPr(BH4)4 show reversible hydrogen storage capacity of 1.65 and 1.04 wt% in the fourth H2 release, whereas that of NaEr(BH4)4 continuously decreases. This is mainly assigned to formation of metal hydrides and possibly slower formation of sodium borohydride. The dehydrogenated state clearly contains rare-earth metal borides, which stabilize boron in the dehydrogenated state

Study of the power supply situation for an improved PFW system (temporary solution)

In this work, a new type of addition reaction between La(BH$_4$)$_3$ and LiX, X = Cl, Br, I, is used to synthesize LiLa(BH$_4$)$_3$Cl and two new compounds LiLa(BH$_4$)$_3$X, X = Br, I. This method increases the amounts of LiLa(BH$_4$)$_3$X and the sample purity. The highest Li-ion conductivity is observed for LiLa(BH$_4$)$_3$Br, 7.74 × 10$^{–5}$ S/cm at room temperature (RT) and 1.8 × 10$^{–5´3}$ S/cm at 140 °C with an activation energy of 0.272 eV. Topological analysis suggests a new lithium ion conduction pathway with two new different types of bottleneck windows. The sizes of these windows reveal an opposite size change with increasing lattice parameter, that is, increasing size of the halide ion in the structure. Thus, we conclude that the sizes of both windows are important for the lithium ion conduction in LiLa(BH$_4$)$_3$X compounds. The lithium ion conductivity is measured over one to three heating cycles and with different contacts (gold or carbon) between the electrodes and the electrolyte. Moreover, $^{11}$B MAS NMR is used to verify the contents of the samples, whereas thermogravimetric analysis shows 4.8 and 3.6 wt % of hydrogen release for LiLa(BHH$_4$)$_3$Cl and LiLa(BHH$_4$)$_3$Br in the temperature range RT to 400 °C

Synthesis, structure and properties of new bimetallic sodium and potassium lanthanum borohydrides

Two new bimetallic sodium or potassium lanthanum borohydrides, NaLa(BH4)4 and K3La(BH4)6, are formed using La(BH4)3 free of metal halide by-products. NaLa(BH4)4 crystallizes in an orthorhombic crystal system with unit cell parameters, a = 6.7987(19), b = 17.311(5), c = 7.2653(19) Å and space group symmetry Pbcn. This compound has a new structure type built from brucite-like layers of octahedra (hcp packing of anions) with half of the octahedral sites empty leading to octahedral chains similar to rutile (straight chains) or α-PbO2 (zig-zag chains). K3La(BH4)6 crystallizes in the monoclinic crystal system with unit cell parameters a = 7.938(2), b = 8.352(2), c = 11.571(3) Å, β = 90.19(6)° and space group P21/n with a double-perovskite type structure. Thermogravimetric analysis shows a mass loss of 5.86 and 2.83 wt% for NaLa(BH4)4 and K3La(BH4)6, respectively, in the temperature range of room temperature to 400 °C. Mass spectrometry shows that hydrogen release starts at 212 and 275 °C for NaLa(BH4)4 and K3La(BH4)6, respectively and confirms that no diborane is released. Sieverts' measurements reveal that 2.03 and 0.49 wt% of hydrogen can be released from the NaLa(BH4)4 and K3La(BH4)6, respectively, during the second hydrogen desorption cycle at the selected physical condition for hydrogen absorption

Reversibility of LiBH₄ Facilitated by the LiBH₄–Ca(BH₄)₂ Eutectic

The hydrogen storage properties of eutectic melting 0.68LiBH₄–0.32Ca­(BH₄)₂ (LiCa) as bulk and nanoconfined into a high surface area, <i>S</i>_BET = 2421 ± 189 m²/g, carbon aerogel scaffold, with an average pore size of 13 nm and pore volume of <i>V</i>_tot = 2.46 ± 0.46 mL/g, is investigated. Hydrogen desorption and absorption data were collected in the temperature range of RT to 500 °C (Δ<i>T</i>/Δ<i>t</i> = 5 °C/min) with the temperature then kept constant at 500 °C for 10 h at hydrogen pressures in the range of 1–8 and 134–144 bar, respectively. The difference in the maximum H₂ release rate temperature, <i>T</i>_max, between bulk and nanoconfined LiCa during the second cycle is Δ<i>T</i>_max ≈ 40 °C, which over five cycles becomes smaller, Δ<i>T</i>_max ≈ 10 °C. The high temperature, <i>T</i>_max ≈ 455 °C, explains the need for high temperatures for rehydrogenation in order to obtain sufficiently fast reaction kinetics. This work also reveals that nanoconfinement has little effect on the later cycles and that nanoconfinement of pure LiBH₄ has a strong effect in only the first cycle of H₂ release. The hydrogen storage capacity is stable for bulk and nanoconfined LiCa in the second to the fifth cycle, which contrasts to nanoconfined LiBH₄ where the H₂ storage capacity continuously decreases. Bulk and nanoconfined LiCa have hydrogen storage capacities of 5.4 and 3.7 wt % H₂ in the fifth H₂ release, which compare well with the calculated hydrogen contents of LiBH₄ only and in LiCa, which are 5.43 and 3.69 wt % H₂, respectively. Thus, decomposition products of Ca­(BH₄)₂ appear to facilitate the full reversibility of the LiBH₄, and this approach may lead to new hydrogen storage systems with stable energy storage capacity over multiple cycles of hydrogen release and uptake

Li₅(BH₄)₃NH: Lithium-Rich Mixed Anion Complex Hydride

The Li₅(BH₄)₃NH complex hydride, obtained by ball milling LiBH₄ and Li₂NH in various molar ratios, has been investigated. Using X-ray powder diffraction analysis the crystalline phase has been indexed with an orthorhombic unit cell with lattice parameters <i>a</i> = 10.2031(3), <i>b</i> = 11.5005(2), and <i>c</i> = 7.0474(2) Å at 77 °C. The crystal structure of Li₅(BH₄)₃NH has been solved in space group <i>Pnma</i>, and refined coupling density functional theory (DFT) and synchrotron radiation X-ray powder diffraction data have been obtained for a 3LiBH₄:2Li₂NH ball-milled and annealed sample. Solid-state nuclear magnetic resonance measurements confirmed the chemical shifts calculated by DFT from the solved structure. The DFT calculations confirmed the ionic character of this lithium-rich compound. Each Li⁺ cation is coordinated by three BH₄^– and one NH^2– anion in a tetrahedral configuration. The room-temperature ionic conductivity of the new orthorhombic compound is close to10^–6 S/cm at room temperature, with activation energy of 0.73 eV

Design of a Nanometric AlTi Additive for MgB₂‑Based Reactive Hydride Composites with Superior Kinetic Properties

Solid-state hydride compounds are a promising option for efficient and safe hydrogen-storage systems. Lithium reactive hydride composite system 2LiBH₄ + MgH₂/2LiH + MgB₂ (Li-RHC) has been widely investigated owing to its high theoretical hydrogen-storage capacity and low calculated reaction enthalpy (11.5 wt % H₂ and 45.9 kJ/mol H₂). In this paper, a thorough investigation into the effect of the formation of nano-TiAl alloys on the hydrogen-storage properties of Li-RHC is presented. The additive 3TiCl₃·AlCl₃ is used as the nanoparticle precursor. For the investigated temperatures and hydrogen pressures, the addition of ∼5 wt % 3TiCl₃·AlCl₃ leads to hydrogenation/dehydrogenation times of only 30 min and a reversible hydrogen-storage capacity of 9.5 wt %. The material containing 3TiCl₃·AlCl₃ possesses superior hydrogen-storage properties in terms of rates and a stable hydrogen capacity during several hydrogenation/dehydrogenation cycles. These enhancements are attributed to an in situ nanostructure and a hexagonal AlTi₃ phase observed by high-resolution transmission electron microscopy. This phase acts in a 2-fold manner, first promoting the nucleation of MgB₂ upon dehydrogenation and second suppressing the formation of Li₂B₁₂H₁₂ upon hydrogenation/dehydrogenation cycling