Fluoride substitution in LiBH₄ is studied by investigation of LiBH₄-LiBF₄ mixtures (9:1 and 3:1). Decomposition was followed by in-situ synchrotron radiation X-ray diffraction (in-situ SR-PXD), thermogravimetric analysis and differential scanning calorimetry with gas analysis (TGA/DSC-MS) and in-situ infrared spectroscopy (in-situ FTIR). Upon heating, fluoride substituted LiBH₄ forms (LiBH_4-xF_x) and decomposition occurs, releasing diborane and solid decomposition products. The decomposition temperature is reduced more than fourfold relative to the individual constituents, with decomposition commencing at T / °C = 80 °C. The degree of fluoride substitution is quantified by sequential Rietveld refinement and shows a selective manner of substitution. In-situ FTIR experiments reveal formation of bands originating from LiBH_4-xF_x. Formation of LiF and observation of diborane release implies that the decomposing materials have a composition that facilitates formation of diborane and LiF, i.e. LiBH_4-xF_x (LiBH₃F). An alternative approach for fluoride substitution was performed, by addition of Et₃N∙3HF to LiBH₄, yielding extremely unstable products. Spontaneous decomposition indicates fluoride substitution to have occurred. From our point of view, this is the most significant destabilization effect seen for borohydride materials so far.

Hydrogen production from waste feedstocks using supercritical water gasification (SCWG) is a promising approach towards cleaner fuel production and a solution for hard to treat wastes. In this study, the catalytic co-gasification of starch and catechol as models of carbohydrates and phenol compounds was investigated in a batch reactor at 28 MPa, 400–500 °C, from 10 to 30 min. The effects of reaction conditions, and the addition of calcium oxide (CaO) as a carbon dioxide (CO₂) sorbent and TiO₂ as catalyst on the gas yields and product distribution were investigated. Employing TiO₂ as a catalyst alone had no significant effect on the H₂ yield but when combined with CaO increased the hydrogen yield by 35% and promoted higher total organic carbon (TOC) reduction efficiencies. The process liquid effluent was characterized using GC–MS, with the results showing that the major non-polar components were phenol, substituted phenols, and cresols. An overall reaction scheme is provided.

A new potassium scandium borohydride, KSc(BH₄)₄, is presented and characterized by a combination of in situ synchrotron radiation powder X-ray diffraction, thermal analysis, and vibrational and NMR spectroscopy. The title compound, KSc(BH₄)₄, forms at ambient conditions in ball milled mixtures of potassium borohydride and ScCl₃ together with a new ternary chloride K₃ScCl₆, which is also structurally characterized. This indicates that the formation of KSc(BH₄)₄ differs from a simple metathesis reaction, and the highest scandium borohydride yield (~31 mol %) can be obtained with a reactant ratio KBH₄:ScCl₃ of 2:1. KSc(BH₄)₄ crystallizes in the orthorhombic crystal system, a = 11.856(5), b = 7.800(3), c = 10.126(6) Ã…, V = 936.4(8) Ã…³ at RT, with the space group symmetry Pnma. KSc(BH₄)₄ has a BaSO₄ type structure where the BH₄ tetrahedra take the oxygen positions. Regarding the packing of cations, K⁺, and complex anions, [Sc(BH₄)₄]^−, the structure of KSc(BH₄)₄ can be seen as a distorted variant of orthorhombic neptunium, Np, metal. Thermal expansion of KSc(BH₄)₄ in the temperature range RT to 405 K is anisotropic, and the lattice parameter b shows strong nonlinearity upon approaching the melting temperature. The vibrational and NMR spectra are consistent with the structural model, and previous investigations of the related compounds ASc(BH₄)₄ with A = Li, Na. KSc(BH₄)₄ is stable from RT up to ~405 K, where the compound melts and then releases hydrogen in two rapid steps approximately at 460−500 K and 510−590 K. The hydrogen release involves the formation of KBH₄, which reacts with K₃ScCl₆ and forms a solid solution, K(BH₄)_1−xCl_x. The ternary potassium scandium chloride K₃ScCl₆ observed in all samples has a monoclinic structure at room temperature, P2₁/a, a = 12.729(3), b = 7.367(2), c = 12.825(3) Ã…, β = 109.22(2)°, V = 1135.6(4) Ã…³, which is isostructural to K₃MoCl₆. The monoclinic polymorph transforms to cubic at 635 K, a = 10.694 Ã… (based on diffraction data measured at 769 K), which is isostructural to the high temperature phase of K₃YCl₆.

The decomposition pathway in LiBH₄−MgH₂ reactive hydride composites was investigated systematically as a function of pressure and temperature. Individual decomposition of MgH2 and LiBH4 is observed at higher temperatures and low pressures (T ≥ 450 °C and p(H₂) ≤ 3 bar), whereas simultaneous desorption of H₂ from LiBH₄ and formation of MgB₂ was observed at 400 °C and a hydrogen backpressure of p(H₂) = 5 bar. The simultaneous desorption of H₂ from LiBH₄ and MgH₂ without intermediate formation of metallic Mg could not be observed. In situ X-ray diffraction (XRD) and infrared (IR) spectroscopy reveal the present crystalline and amorphous phases.

A new alkaline transition-metal borohydride, NaSc(BH₄)₄, is presented. The compound has been studied using a combination of in situ synchrotron radiation powder X-ray diffraction, thermal analysis, and vibrational and NMR spectroscopy. NaSc(BH₄)₄ forms at ambient conditions in ball-milled mixtures of sodium borohydride and ScCl₃. A new ternary chloride Na₃ScCl₆ (P2₁/n, a = 6.7375(3) Ã…, b = 7.1567(3) Ã…, c = 9.9316(5) Ã…, β = 90.491(3)°, V = 478.87(4) Ã…³), isostructural to Na₃TiCl₆, was identified as an additional phase in all samples. This indicates that the formation of NaSc(BH₄)₄ differs from a simple metathesis reaction, and the highest scandium borohydride yield (22 wt %) was obtained with a reactant ratio of ScCl₃/NaBH₄ of 1:2. NaSc(BH₄)₄ crystallizes in the orthorhombic crystal system with the space group symmetry Cmcm (a = 8.170(2) Ã…, b = 11.875(3) Ã…, c = 9.018(2) Ã…, V = 874.9(3) Ã…³). The structure of NaSc(BH₄)₄ consists of isolated homoleptic scandium tetraborohydride anions, [Sc(BH₄)₄]^–, located inside slightly distorted trigonal Na₆ prisms (each second prism is empty, triangular angles of 55.5 and 69.1°). The experimental results show that each Sc³⁺ is tetrahedrally surrounded by four BH₄ tetrahedra with a 12-fold coordination of H to Sc, while Na⁺ is surrounded by six BH₄ tetrahedra in a quite regular octahedral coordination with a (6 + 12)-fold coordination of H to Na. The packing of Na⁺ cations and [Sc(BH₄)₄]^– anions in NaSc(BH₄)₄ is a deformation variant of the hexagonal NiAs structure type. NaSc(BH₄)₄ is stable from RT up to ∼410 K, where the compound melts and then releases hydrogen in two rapidly occurring steps between 440 and 490 K and 495 and 540 K. Thermal expansion of NaSc(BH₄)₄ between RT and 408 K is anisotropic, and lattice parameter b shows strong anomaly close to the melting temperature.