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Instruments / Technical Area	Publication Details	Published
I11-High Resolution Powder Diffraction	Structural diversity and trends in properties of an array of hydrogen-rich ammonium metal borohydrides Jakob B. Grinderslev , Lars H. Jepsen , Young-su Lee , Kasper Moller , Young Whan Cho , Radovan Cerny , Torben Jensen Inorganic Chemistry DOI: 10.1021/acs.inorgchem.0c01797 Diamond Proposal Number(s): [12714, 14015] Show Abstract ▼ Abstract: Metal borohydrides are a fascinating and continuously expanding class of materials, showing promising applications within many different fields of research. This study presents 17 derivatives of the hydrogen-rich ammonium borohydride, NH4BH4, which all exhibit high gravimetric hydrogen densities (>9.2 wt % of H2). A detailed insight into the crystal structures combining X-ray diffraction and density functional theory calculations exposes an intriguing structural variety ranging from three-dimensional (3D) frameworks, 2D-layered, and 1D-chainlike structures to structures built from isolated complex anions, in all cases containing NH4+ countercations. Dihydrogen interactions between complex NH4+ and BH4– ions contribute to the structural diversity and flexibility, while inducing an inherent instability facilitating hydrogen release. The thermal stability of the ammonium metal borohydrides, as a function of a range of structural properties, is analyzed in detail. The Pauling electronegativity of the metal, the structural dimensionality, the dihydrogen bond length, the relative amount of NH4+ to BH4–, and the nearest coordination sphere of NH4+ are among the most important factors. Hydrogen release usually occurs in three steps, involving new intermediate compounds, observed as crystalline, polymeric, and amorphous materials. This research provides new opportunities for the design and tailoring of novel functional materials with interesting properties.	Aug 2020
I11-High Resolution Powder Diffraction	Ammonium–ammonia complexes, N2H7+, in ammonium closo-borate ammines: synthesis, structure, and properties Jakob B. Grinderslev , Young-su Lee , Mark Paskevicius , Kasper Moller , Yigang Yan , Young Whan Cho , Torben Jensen Inorganic Chemistry DOI: 10.1021/acs.inorgchem.0c01257 Diamond Proposal Number(s): [15781, 17433] Show Abstract ▼ Abstract: Metal closo-borates have recently received significant attention due to their potential applications as solid-state ionic conductors. Here, the synthesis, crystal structures, and properties of (NH4)2B10H10·xNH3 (x = 1/2, 1 (α and β)) and (NH4)2B12H12·xNH3 (x = 1 and 2) are reported. In situ synchrotron radiation powder X-ray diffraction allows for the investigation of structural changes as a function of temperature. The structures contain the complex cation N2H7+, which is rarely observed in solid materials, but can be important for proton conductivity. The structures are optimized by density functional theory (DFT) calculations to validate the structural models and provide detailed information about the hydrogen positions. Furthermore, the hydrogen dynamics of the complex cation N2H7+ are studied by molecular dynamics simulations, which reveals several events of a proton transfer within the N2H7+ units. The thermal properties are investigated by thermogravimetry and differential scanning calorimetry coupled with mass spectrometry, revealing that NH3 is released stepwise, which results in the formation of (NH4)2BnHn (n = 10 and 12) during heating. The proton conductivity of (NH4)2B12H12·xNH3 (x = 1 and 2) determined by electrochemical impedance spectroscopy is low but orders of magnitude higher than that of pristine (NH4)2B12H12. The thermal stability of the complex cation N2H7+ is high, up to 170 °C, which may provide new possible applications of these proton-rich materials.	Jul 2020
I11-High Resolution Powder Diffraction	Synthesis, structure and NH3 sorption properties of mixed Mg1-xMnx(NH3)6Cl2 ammines Perizat Berdiyeva , Anastasiia Karabanova , Jakob B. Grinderslev , Rune E. Johnsen , Didier Blanchard , Bjørn C. Hauback , Stefano Deledda Energies 13 DOI: 10.3390/en13112746 Diamond Proposal Number(s): [21804] Open Access Show Abstract ▼ Abstract: This paper describes the synthesis, crystal structure, and NH3 sorption properties of Mg1-xMnx(NH3)6Cl2 (x = 0–1) mixed metal halide ammines, with reversible NH3 storage capacity in the temperature range 20–350 °C. The stoichiometry (x) dependent NH3 desorption temperatures were monitored using in situ synchrotron radiation powder X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry. The thermal analyses reveal that the NH3 release temperatures decrease in the mixed metal halide ammines in comparison to pure Mg(NH3)6Cl2, approaching the values of Mn(NH3)6Cl2. Desorption occurs in three steps of four, one and one NH3 moles, with the corresponding activation energies of 54.8 kJ⋅mol-1, 73.2 kJ⋅mol-1 and 91.0 kJ⋅mol-1 in Mg0.5Mn0.5(NH3)6Cl2, which is significantly lower than the NH3 release activation energies of Mg(NH3)6Cl2 (Ea = 60.8 kJ⋅mol-1, 74.8 kJ⋅mol-1 and 91.8 kJ⋅mol-1). This work shows that Mg1-xMnx(NH3)yCl2 (x = 0 to 1, y = 0 to 6) is stable within the investigated temperature range (20–350 °C) and also upon NH3 cycling.	May 2020
I11-High Resolution Powder Diffraction	Ammonia-assisted fast Li-ion conductivity in a new hemiammine lithium borohydride, LiBH 4 ·1/2NH 3 Yigang Yan , Jakob B. Grinderslev , Young-su Lee , Mathias Jorgensen , Young Whan Cho , Radovan Cerny , Torben Jensen Chemical Communications 56, 3971 - 3974 DOI: 10.1039/C9CC09990E Show Abstract ▼ Abstract: Hemiammine lithium borohydride, LiBH4·1/2NH3, is characterized and a new Li+ conductivity mechanism is identified. It exhibits a Li+ conductivity of 7 × 10−4 S cm−1 at 40 °C in the solid state and 3.0 × 10−2 S cm−1 at 55 °C after melting. The molten state of LiBH4·1/2NH3 has a high viscosity and can be mechanically stabilized in nano-composites with inert metal oxides and other hydrides making it a promising battery electrolyte.	Apr 2020
I11-High Resolution Powder Diffraction	The mechanism of Mg 2+ conduction in ammine magnesium borohydride promoted by a neutral molecule Yigang Yan , Wilke Dononelli , Mathias Jorgensen , Jakob B. Grinderslev , Young-su Lee , Young Whan Cho , Radovan Cerny , Bjørk Hammer , Torben R. Jensen Physical Chemistry Chemical Physics 66 DOI: 10.1039/D0CP00158A Show Abstract ▼ Abstract: Light weight and cheap electrolytes with fast multi-valent ion conductivity can pave the way for future high-energy density solid-state batteries, beyond the lithium-ion battery. Here we present the mechanism of Mg-ion conductivity of monoammine magnesium borohydride, Mg(BH4)2·NH3. Density functional theory calculations (DFT) reveal that the neutral molecule (NH3) in Mg(BH4)2·NH3 is exchanged between the lattice and interstitial Mg2+ facilitated by a highly flexible structure, mainly owing to a network of di-hydrogen bonds, N–Hδ+⋯−δH–B and the versatile coordination of the BH4− ligand. DFT shows that di-hydrogen bonds in inorganic matter and hydrogen bonds in bio-materials have similar bond strengths and bond lengths. As a result of the high structural flexibiliy, the Mg-ion conductivity is dramatically improved at moderate temperature, e.g. σ(Mg2+) = 3.3 × 10−4 S cm−1 at T = 80 °C for Mg(BH4)2·NH3, which is approximately 8 orders of magnitude higher than that of Mg(BH4)2. Our results may inspire a new approach for the design and discovery of unprecedented multivalent ion conductors.	Mar 2020
I11-High Resolution Powder Diffraction	Probing the local symmetry of Tb3+ in borohydrides using luminescence spectroscopy Julien Christmann , Asma Mansouri , Jakob B. Grinderslev , Torben Jensen , Hans Hagemann Journal Of Luminescence DOI: 10.1016/j.jlumin.2020.117065 Diamond Proposal Number(s): [15781] Show Abstract ▼ Abstract: Rare-earth borohydrides have recently attracted a strong interest as potential hydrogen storage materials. While the local structure of the BH4− ion can be probed using vibrational spectroscopy, the local structure of the rare-earth ion can be studied using luminescence spectroscopy. This is reported here for Tb(BH4)3 and its solvate with S(CH3)2. The spectra clearly show smaller CF splittings for the unsolvated compound. These experimental data are compared with recent DFT + U calculations of the energy levels and CF splittings for Tb(BH4)3 and show that these calculations significantly overestimate the experimental results.	Jan 2020
I11-High Resolution Powder Diffraction	Potassium octahydridotriborate: diverse polymorphism in a potential hydrogen storage material and potassium ion conductor Jakob B. Grinderslev , Kasper Moller , Yigang Yan , Xi-meng Chen , Yongtao Li , Hai-wen Li , Wei Zhou , Jørgen Skibsted , Xuenian Chen , Torben Jensen Dalton Transactions 46 DOI: 10.1039/C9DT00742C Diamond Proposal Number(s): [17433] Show Abstract ▼ Abstract: Octahydridoborate, i.e. [B3H8]− containing compounds, have recently attracted interest for hydrogen storage. In the present study, the structural, hydrogen storage, and ion conductivity properties of KB3H8 have been systematically investigated. Two distinct polymorphic transitions are identified for KB3H8 from a monoclinic (α) to an orthorhombic (α′) structure at 15 °C via a second-order transition and eventually to a cubic (β) structure at 30 °C by a first-order transition. The β-polymorph of KB3H8 displays a high degree of disorder of the [B3H8]− anion, which facilitates increased cation mobility, reaching a K+ conductivity of ∼10−7 S cm−1 above 100 °C. β-KB3H8 starts to release hydrogen at ∼160 °C, simultaneously with the release of B5H9 and trace amounts of B2H6. KBH4 and K3(BH4)(B12H12) are identified as crystalline decomposition products above 200 °C, and the formation of a KBH4 deficient structure of K3−x(BH4)1−x(B12H12) is observed at elevated temperature. The hydrogen-uptake properties of a KB3H8–2KH composite have been examined under 380 bar H2, resulting in the formation of KBH4 at T ≥ 150 °C along with higher metal hydridoborates, i.e. K2B9H9, K2B10H10, and K2B12H12.	May 2019
I11-High Resolution Powder Diffraction	Trends in synthesis, crystal structure, and thermal and magnetic properties of rare-earth metal borohydrides Jakob B. Grinderslev , Kasper Moller , Martin Bremholm , Torben Jensen Inorganic Chemistry DOI: 10.1021/acs.inorgchem.8b03258 Diamond Proposal Number(s): [15781] Show Abstract ▼ Abstract: Synthesis, crystal structures, and thermal and magnetic properties of the complete series of halide-free rare-earth (RE) metal borohydrides are presented. A new synthesis method provides high yield and high purity products. Fifteen new metal borohydride structures are reported. The trends in crystal structures, thermal behavior, and magnetic properties for the entire series of RE(BH4)x are compared and discussed. The RE(BH4)x possess a very rich crystal chemistry, dependent on the oxidation state and the ionic size of the rare-earth ion. Due to the lanthanide contraction, there is a significant decrease in the volume of the RE3+-ion with increasing atomic number, which correlates linearly with the unit cell volume of the α- and β-RE(BH4)3 polymorphs and the solvated complexes α-RE(BH4)3·S(CH3)2. The thermal analysis reveals a one-step decomposition pathway in the temperature range from 247 to 277 °C for all RE(BH4)3 except Lu(BH4)3, which follows a three-step decomposition pathway. In contrast, the RE(BH4)2 decompose at higher temperatures in the range 306 to 390 °C due to lower charge density on the rare-earth ion. The RE(BH4)3 show increasing stability with increasing Pauling electronegativity, which contradicts other main group and transition metal borohydrides. The majority of the compounds follow Curie–Weiss paramagnetic behavior down to 3 K with weak antiferromagnetic interactions and magnetic moments in accord with those of isolated 4f ions. Some of the RE(BH4)x display varying degrees of temperature-dependent magnetic moments due to low-lying excited stated induced by crystal field effects. Additionally, a weak antiferromagnetic ordering is observed in Gd(BH4)3, indicating superexchange through a borohydride group.	Apr 2019
I11-High Resolution Powder Diffraction	A NaAlH 4 -Ca(BH 4 ) 2 composite system for hydrogen storage Kasper T. Moller , Jakob B. Grinderslev , Torben R. Jensen Journal Of Alloys And Compounds DOI: 10.1016/j.jallcom.2017.05.264 Diamond Proposal Number(s): [12714] Show Abstract ▼ Abstract: Mechanochemical treatment (ball-milling) of NaAlH4-Ca(BH4)2 mixtures leads to partial formation of NaBH4 and Ca(AlH4)2 by a metathesis reaction. The reaction proceeds to different extents depending on the applied ball-milling times, which is confirmed by powder X-ray diffraction and infrared spectroscopy. Additionally, an in-situ synchrotron radiation powder X-ray diffraction study reveals that the metathesis reaction continues due to thermal treatment while the data also supports a two-step decomposition of the formed Ca(AlH4)2. Finally, the reactive hydride composite system was investigated by mass spectrometry and Sieverts' measurement, which reveal release of ∼6 wt% H2 at T < 375 °C.	May 2017

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