Structural and spectroscopic characterization of potassium fluoroborohydrides

Mechanochemical reactions between KBH4 and KBF4 result in the formation of potassium fluoroborohydrides K(BHxF4−x) (x = 0–4), as determined by 11B and 19F solid state NMR. The materials maintain the cubic KBH4 structure. Thermogravimetric (TG) data for a ball-milled sample with KBH4:KBF4 = 3:1 are consistent with only desorption of hydrogen

Structural and spectroscopic characterization of potassium fluoroborohydrides

-Mechanochemical reactions between KBH4 and KBF4 result in the formation of potassium fluoroborohydrides K(BHxF4−x) (x = 0–4), as determined by 11B and 19F solid state NMR. The materials maintain the cubic KBH4 structure. Thermogravimetric (TG) data for a ball-milled sample with KBH4:KBF4 = 3:1 are consistent with only desorption of hydrogen

Enhanced Hydrogen Uptake/Release in 2LiH–MgB2 Composite with Titanium Additives

The influence of different titanium additives on hydrogen sorption in LiH–MgB2 system has been investigated. For all the composites LiH–MgB2–X (X = TiF4, TiO2, TiN, and TiC), prepared by ball milling in molar ratios 2:1:0.1, five hydrogen uptake/release cycles were performed. In-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and attenuated total reflection infrared spectroscopy (ATR-IR) have been used to characterize crystal phases developed during the hydrogen absorption-desorption cycles. All the composites with the titanium additives displayed an improvement of reaction kinetics, especially during hydrogen desorption. The LiH–MgB2–TiO2 system reached a storage of about 7.6 wt % H2 in ~ 1.8 hours for absorption and ~ 2.7 hours for desorption. Using in-situ SR-PXD measurements, magnesium was detected as an intermediate phase during hydrogen desorption for all composites. In the composite with TiF4 addition the formation of new phases (TiB2 and LiF) were observed. Characteristic diffraction peaks of TiO2, TiN and TiC additives were always present during hydrogen absorption-desorption. For all as-milled composites, ATR-IR spectra did not show any signals for borohydrides, while for all hydrogenated composites B–H stretching (2450– 2150 cm-1) and B–H bending (1350–1000 cm-1) bands were exactly the same as for commercial LiBH4.JRC.F.2-Cleaner energ

Nanoconfined 2LiBH(4)-MgH2 Prepared by Direct Melt Infiltration into Nanoporous Materials

Nanoconfined 2LiBH(4)-MgH2 is prepared by direct melt infiltration of bulk 2LiBH(4)-MgH2 into an inert nanoporous resorcinol-formaldehyde carbon aerogel scaffold material. Scanning electron microscopy (SEM) micrographs and energy dispersive X-ray spectroscopy (EDS) mapping reveal homogeneous dispersion of Mg (from MgH2) and B (from LiBH4) inside the carbon aerogel scaffold. Moreover, nanoconfinement of LiBH4 in the carbon aerogel scaffold is confirmed by differential scanning calorimetry (DSC). The hydrogen desorption kinetics of the nanoconfined 2LiBH(4)-MgH2 is significantly improved as compared to bulk 2LiBH(4)-MgH2. For instance, the nanoconfined 2LiBH(4)-MgH2 releases 90% of the total hydrogen storage capacity within 90 mm, whereas the bulk material releases only 34% (at T = 425 degrees C and p(H-2) = 3.4 bar). A reversible gravimetric hydrogen storage capacity of 10.8 wt % H-2, calculated with respect to the metal hydride content, is preserved over four hydrogen release and uptake cycles

Combined X-ray and Raman Studies on the Effect of Cobalt Additives on the Decomposition of Magnesium Borohydride

Magnesium borohydride (Mg(BH4)2) is one of the most promising hydrogen storage materials. Its kinetics of hydrogen desorption, reversibility, and complex reaction pathways during decomposition and rehydrogenation, however, present a challenge, which has been often addressed by using transition metal compounds as additives. In this work the decomposition of Mg(BH4)2 ball-milled with CoCl2 and CoF2 additives, was studied by means of a combination of several in-situ techniques. Synchrotron X-ray diffraction and Raman spectroscopy were used to follow the phase transitions and decomposition of Mg(BH4)2. By comparison with pure milled Mg(BH4)2, the temperature for the \u3b3 \u2192 \u3b5 phase transition in the samples with CoF2 or CoCl2 additives was reduced by 10\u201345 \ub0C. In-situ Raman measurements showed the formation of a decomposition phase with vibrations at 2513, 2411 and 766 cm 121 in the sample with CoF2. Simultaneous X-ray absorption measurements at the Co K-edge revealed that the additives chemically transformed to other species. CoF2 slowly reacted upon heating till ~290 \ub0C, whereas CoCl2 transformed drastically at ~180 \ub0C

Characterization of metal hydrides by in-situ XRD

In-situ synchrotron radiation powder X-ray diffraction (SR-PXD) technique is a powerful tool to gain a deeper understanding of reaction mechanisms in crystalline materials. In this paper, the implementation of a new in-situ SR-PXD cell for solid–gas reactions is described in detail. The cell allows performing measurements in a range of pressure which goes from light vacuum (10−2 bar) up to 200 bar and temperatures from room temperature up to 550 °C. The high precision, with which pressure and temperature are measured, enables to estimate the thermodynamic properties of the observed changes in the crystal structure and phase transformations

Femtosecond Laser-Induced Periodic Surface Structures on 2D Ti-Fe Multilayer Condensates

2D Ti-Fe multilayer preparation has been attracting increased interest due to its ability to form intermetallic compounds between metallic titanium and metallic iron thin layers. In particular, the TiFe compound can absorb hydrogen gas at room temperature. We applied femtosecond laser pulses to heat Ti-Fe multilayer structures to promote the appearance of intermetallic compounds and generate surface nanostructuring. The surface pattern, known as Laser Induced Periodic Surface Structures (LIPSS), can accelerate the kinetics of chemical interaction between solid TiFe and gaseous hydrogen. The formation of LIPSS on Ti-Fe multilayered thin films were investigated using of scanning electron microscopy, photo-electron spectroscopy and X-ray diffraction. To explore the thermal response of the multiple layered structure and the mechanisms leading to surface patterning after irradiating the compound with single laser pulses, theoretical simulations were conducted to interpret the experimental observations