Synthesis Mechanism of Alkali Borohydrides by Heterolytic Diborane Splitting

Similar to alane in alanates, borane species are assumed to be the mass transport intermediate in the hydrogen storage reaction MH + B + 3/2H2 ⇔ MBH4 with M = Li and Na. One possible substep of this reaction is the interaction of diborane with the alkali hydride. In this paper, we unravel the synthesis mechanism of alkali borohydrides by solid−gas reaction of alkali hydrides and diborane gas by H/D isotope labeling of the reaction educts (e.g., LiD + B2H6). The labeling enables us to trace the hydrogen/deuterium atoms in the borohydride product by Raman scattering and in the gas by infrared spectrometry measurements. We conclude that, during the LiBH4 synthesis from LiH, the entire BH4− unit is transferred from the diborane to the Li+ cation. This provides clear evidence for the heterolytic splitting of diborane on alkali hydrides and implies exchange of BH4− with H− ions of the underlying hydride. The detection of Li−H bonds at the surface of newly formed LiBH4 confirms the importance of H− defects for the synthesis of borohydrides

Supercritical N₂ Processing as a Route to the Clean Dehydrogenation of Porous Mg(BH₄)₂

Compounds of interest for chemical hydrogen storage at near ambient conditions are specifically tailored to be relatively unstable and thereby desorb H2 upon heating. Their decomposition must be performed in the absence of impurities to achieve clean dehydrogenation products, which is particularly challenging for an emerging class of microporous complex hydride materials, such as γ-phase Mg­(BH4)2, which exhibits high surface area and readily adsorbs (sometimes undesired) molecular species. We present a novel strategy toward the purification of γ-Mg­(BH4)2 using supercritical nitrogen drying techniques, (1) showing that clean hydrogen can be released from Mg­(BH4)2 under mild conditions and (2) clarifying the origin of diborane among the decomposition products of stable borohydrides, a topic of critical importance for the reversibility and practical applicability of this class of hydrogen storage compounds. This technique is also widely applicable in the pursuit of the high-purity synthesis of other porous, reactive compounds, an exciting future class of advanced functional materials

Single-Component and Binary CO₂ and H₂O Adsorption of Amine-Functionalized Cellulose

A fundamental analysis of single-component and binary CO₂ and H₂O adsorption of amine-functionalized nanofibrillated cellulose is carried out in the temperature range of 283–353 K and at CO₂ partial pressures in the range of 0.02–105 kPa, where the ultralow partial pressure range is relevant for the direct capture of CO₂ from atmospheric air. Single-component CO₂ and H₂O adsorption experimental data are fitted to the Toth and Guggenheim–Anderson–de Boer models, respectively. Corresponding heats of adsorption, derived from explicit solutions of the van’t Hoff equation, are −50 kJ/mol CO₂ and −48.8 kJ/mol H₂O. Binary CO₂/H₂O adsorption measurements for humid air reveal that the presence of H₂O at 2.55 kPa enhances CO₂ adsorption, while the presence of CO₂ at 0.045 kPa does not influence H₂O adsorption. The energy demand of the temperature-vacuum-swing adsorption/desorption cycle for delivering pure CO₂ from air increases significantly with H₂O adsorption and indicates the need to reduce the hygroscopicity of the adsorbent

High Influence of Potassium Bromide on Thermal Decomposition of Ammonia Borane^†

The present paper presents a thorough experimental investigation of mechanistic pathways of thermal decomposition of ammonia borane (AB) and its mixture with KBr. A comparative detection and temperature-dependent <i>in situ</i> monitoring of the decomposition products was done by use of temperature-dependent infrared (IR) spectroscopy of both solid (in transmission through KBr pellets and ATR mode) and gaseous products, thermogravimetry (TG) and evolved gas analysis mass spectroscopy (EGA–MS). This enables discrimination of the processes occurring in the bulk from those in the near-surface level. For the first time, a high influence of the KBr matrix on AB decomposition was found and thoroughly investigated. Although KBr does not change the chemical and physical identity of AB at ambient conditions, it dramatically affects its thermal decomposition pathway. It is found that the presence of KBr not only favors the production of diammoniate of diborane in the induction phase, but also enables an efficient catalysis of AB decomposition by NH₄⁺ ions, present at the KBr–AB interface, which leads to suppression of emission of unwanted gaseous side products other than NH₃. IR spectroscopy was also used to shed a light on the molecular background of the frequently observed, but never investigated increase of the mass of decomposition products

Influence of Molybdenum Oxide Interface Solvent Sensitivity on Charge Trapping in Bilayer Cyanine Solar Cells

Bilayer organic solar cells based on trimethine cyanine donor and C₆₀ acceptor materials have been fabricated by coating the trimethine dye from solution on molybdenum oxide (MoO₃) anode buffer layer. The choice of deposition solvent drastically influences device performance, with 2,2,3,3-tetrafluoro-1-propanol (TFP) reducing the fill factor and power conversion efficiency of the device by 36 and 21%, respectively, as compared to chlorobenzene. In the case of TFP, extraction of photogenerated charge carriers by linearly increasing voltage (photo-CELIV) and capacitance–voltage analysis revealed the formation of a hole trapping zone at the molybdenum oxide interface which is also responsible for the S-shape current–voltage curve under white light irradiation. The transient charge extraction signal originating from trapped holes at the MoO₃ interface could be clearly distinguished from the one relating to hole mobility in cyanine films using photo-CELIV measurements with varying delay times

Synthesis and Electronic Structure of Mid-Infrared Absorbing Cu₃SbSe₄ and Cu_<i>x</i>SbSe₄ Nanocrystals

Aliovalent I–V–VI semiconductor nanocrystals are promising candidates for thermoelectric and optoelectronic applications. Famatinite Cu3SbSe4 stands out due to its high absorption coefficient and narrow band gap in the mid-infrared spectral range. This paper combines experiment and theory to investigate the synthesis and electronic structure of colloidal CuxSbSe4 nanocrystals. We achieve predictive composition control of size-uniform CuxSbSe4 (x = 1.9–3.4) nanocrystals. Density functional theory (DFT)-parametrized tight-binding simulations on nanocrystals show that the more the Cu-vacancies, the wider the band gap of CuxSbSe4 nanocrystals, a trend which we also confirm experimentally via FTIR spectroscopy. We show that SbCu antisite defects can create mid-gap states, which may give rise to sub-bandgap absorption. This work provides a detailed study of CuxSbSe4 nanocrystals and highlights the potential opportunities as well as challenges for their application in infrared devices

Complex Hydrides with (BH₄)⁻ and (NH₂)⁻ Anions as New Lithium Fast-Ion Conductors

Complex Hydrides with (BH4)− and (NH2)− Anions as New Lithium Fast-Ion Conductor

Photochemical Creation of Covalent Organic 2D Monolayer Objects in Defined Shapes <i>via</i> a Lithographic 2D Polymerization

In this work we prepare Langmuir–Blodgett monolayers with a trifunctional amphiphilic anthraphane monomer. Upon spreading at the air/water interface, the monomers self-assemble into 1 nm-thin monolayer islands, which are highly fluorescent and can be visualized by the naked eye upon excitation. In situ fluorescence spectroscopy indicates that in the monolayers, all the anthracene units of the monomers are stacked face-to-face forming excimer pairs, whereas at the edges of the monolayers, free anthracenes are present acting as edge groups. Irradiation of the monolayer triggers [4 + 4]-cycloadditions among the excimer pairs, effectively resulting in a two-dimensional (2D) polymerization. The polymerization reaction also completely quenches the fluorescence, allowing to draw patterns on the monomer monolayers. More interestingly, after transferring the monomer monolayer on a solid substrate, by employing masks or the laser of a confocal scanning microscope, it is possible to arbitrarily select the parts of the monolayer that one wants to polymerize. The unpolymerized regions can then be washed away from the substrate, leaving 2D macromolecular monolayer objects of the desired shape. This photolithographic process employs 2D polymerizations and affords 1 nm-thin coatings

Diyne-Functionalized Fullerene Self-Assembly for Thin Film Solid-State Polymerization

C₆₀ fullerene derivatives bearing aliphatic chains can self-assemble into versatile supramolecular structures. Cross-linking of such self-assembled morphologies is an attractive approach to enhance the structural stability of these self-organized structures. We describe the synthesis of a C₆₀ functionalized with a single alkyl chain bearing a diacetylene moiety. In a thin film, the molecule self-assembles into lamellar arrays. The character of the side chain attached to the fullerene is key to the observed packing ability. The stabilization proceeds through solid-state polymerization of the diacetylene moieties. By blending the fullerene derivative with a cyanine dye, various nanostructured fullerene morphologies are obtained that can be selectively stabilized by thermal polymerization. These films can serve as basis for nanostructured fullerene scaffolds that can find applications in optics and electronics

Correction to Photochemical Creation of Covalent Organic 2D Monolayer Objects in Defined Shapes <i>via</i> a Lithographic 2D Polymerization

Correction to Photochemical Creation of Covalent Organic 2D Monolayer Objects in Defined Shapes via a Lithographic 2D Polymerizatio