Structural and dynamic studies of Pr(11^{11}BH4_{4})3_{3}

Rare earth borohydrides RE (BH4)(3) are studied in the context of energy storage, lumines-cence and magnetic applications. We have investigated the structural behavior of pra-seodymium borohydride Pr ((BH4)-B-11)(3) containing B-11 isotope because of the previously reported negative thermal expansion. Differential scanning calorimetry (DSC), in-situ var-iable temperature synchrotron radiation powder X-ray diffraction (SR-PXD) and infrared studies reveal that Pr ((BH4)-B-11)(3) undergoes to a volume contraction during the phase tran-sition from alpha alpha-Pr ((BH4)-B-11)(3) to rhombohedral r-Pr ((BH4)-B-11)(3) phase upon heating to 493 K. Surprisingly, the phase transition persists upon cooling at room temperature. Vibrational analysis also shows that the stretching frequency of BH4-3; anion does not change upon heating which indicates that the B-H bond length remains constant during the structural phase transition from alpha-Pr ((BH4)-B-11)(3) to r-Pr ((BH4)-B-11)(3) phase. Additionally, the energy barrier of reorientation motion of the BH4- anion in the alpha-phase was estimated to be ca 23 kJ/mol by quasi-elastic neutron scattering (QENS) and Raman spectroscopy. (C) 2021 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC

Novel and Scalable Synthesis of BnHxz- Boron Clusters as Solid-State Electrolytes for Sodium Batteries and their Detailed Study for Hydrogen Storage Applications

All-solid-state batteries (ASSBs) promise higher power and energy density compared to batteries based on liquid electrolytes. Recently, a stable 3V ASSB based on the super ionic conductor (1mS cm-1 near room temperature) Na4(B12H12)(B10H10) has demonstrated excellent cycling stability. This electrolyte Na4(B12H12)(B10H10) can be obtained directly using the 5 steps, scalable and solution-based synthesis shown in scheme 1 (TEA = Et4N+). The use of the wet chemistry in the final step allows the solution processing of the solid electrolyte and to improve the contacts with the cathode material during assembly of the battery. This new synthesis is a cost efficient synthesis for the precursors Na2B10H10 and Na2B12H12 which are commercially very expensive. Two key parameters to tune the kinetics and selectivity of this solvolthermal synthesis of closo-hydroborates were identified: the choice of the counter cation, tetraethylammonium ((C2H5)4N+, TEA+) vs tetrabutylammonium (TBA+), and the solvent

An alternative approach to the synthesis of NaB₃H₈ and Na₂B₁₂H₁₂ for solid electrolyte applications

Alkaline or alkaline earth octahydrotriborate M(B3H8)x and dodecahydro-closo-dodecaborate MxB12H12 (M = Li, Na, Mg or Ca with x = 1 or 2) have recently attracted a lot of interest for hydrogen storage and solid electrolyte applications. Nevertheless, their syntheses are still a roadblock for large scale applications. In this paper we propose a novel approach for their syntheses starting from the cheapest borohydride NaBH4. The process involves first the solvothermal synthesis of tetrabutylammonium octahydrotriborate (C4H9)4NB3H8 (TBAB3H8) being the basis for the syntheses of the others boranes. Starting from TBAB3H8, we have synthesized pure and unsolvated NaB3H8 by salt metathesis reaction with sodium tetraphenylborate. Then, we have successfully obtained Na2B12H12 by solvothermal decomposition of NaB3H8. This approach has shown to be quantitative and reproducible, which could lead to the development of these boranes in real life applications

Experimental investigation of Mg(B₃H₈)₂ dimensionality, materials for energy storage applications

Mg(B3H8)2 is a crucial reaction intermediate in the thermal decomposition of the hydrogen storage material Mg(BH4)2 and is discussed as a potential solid-state Mg-ion conductor. We successfully synthesized unsolvated Mg(B3H8)2 and highlight that Mg(B3H8)2 exists mainly as a low-dimensional solid. In addition, the Mg2+ conductivity was evaluated to be 1.4.10−4 S cm−1 at 80 °C

Direct Solution‐Based Synthesis of Na₄(B₁₂H₁₂)(B₁₀H₁₀) Solid Electrolyte

All‐solid‐state batteries (ASSBs) promise higher power and energy density than batteries based on liquid electrolytes. Recently, a stable 3 V ASSB based on the super ionic conductor (1 mS cm−1 near room temperature) Na4(B12H12)(B10H10) has demonstrated excellent cycling stability. This study concerns the development of a five‐step, scalable, and solution‐based synthesis of Na4(B12H12)(B10H10). The use of a wet chemistry approach allows solution processing with high throughput and addresses the main drawbacks for this technology, specifically, the limited electrode–electrolyte contact and high cost. Moreover, a cost‐efficient synthesis of the expensive precursors Na2B10H10 and Na2B12H12 is also achieved through the same process. The mechanism of the reactions is investigated and two key parameters to tune the kinetics and selectivity are highlighted: the choice of counter cation (tetraethylammonium) and solvent

Synthesis, Characterization, and Crystal Structures of Two New Manganese Aceto EMIM Ionic Compounds with Chains of Mn²⁺ Ions Coordinated Exclusively by Acetate

We synthesized and determined crystal structures of two manganese(II) aceto EMIM coordination compounds with simplified empirical formulas Mn4(OAc)10 [EMIM]2 and Mn4(OAc)10 [EMIM] 2 ·2H2O. Both compounds feature extended chains of Mn 2+ octahedrally coordinated exclusively by acetate anions, which has been observed for the first time. The EMIM moieties and water molecules participate in hydrogen bonding with acetate anions but do not directly interact with the metal cation. Both compounds have melting temperatures around 120°C and can be considered as (non-room-temperature) ionic liquids. The structural arrangement represented by the two title compounds is robust in terms of accommodating other types of cations and allows for tuning of physical properties of the ionic liquid by means of cation substitution. Thermal analysis results obtained using TGA−DSC and VT IR suggest melting phase transitions around 120°C, followed by structural rearrangement in the molten state taking place around 140−160°C. CompoundsI andII have a higher thermal stability range compared to [EMIM][OAc] ionic liquid, with an onset decomposition temperature above 260 °

Pressure-induced phase transitions in Na2B12H12, structural investigation on a candidate for solid-state electrolyte

closo-Borates, such as Na2B12H12, are an emerging class of ionic conductors that show promising chemical, electrochemical and mechanical properties as electrolytes in all-solid-state batteries. Motivated by theoretical predictions, high-pressure in situ powder X-ray diffraction on Na2B12H12 was performed and two high-pressure phases are discovered. The first phase transition occurs at 0.5 GPa and it is persistent to ambient pressure, whereas the second transition takes place between 5.7 and 8.1 GPa and it is fully reversible. The mechanisms of the transitions by means of group theoretical analysis are unveiled. The primary order parameters are identified and the stability at ambient pressure of the first polymorph is explained by density functional theory calculations. Finally, the parameters relevant to engineer and build an all-solid-state battery, namely, the bulk modulus and the coefficient of the thermal expansion are reported. The relatively low value of the bulk modulus for the first polymorph (14 GPa) indicates a soft material which allows accommodation of the volume change of the cathode during cycling

Study of the Temperature- and Pressure-Dependent Structural Properties of Alkali Hydrido closo-borate Compounds

In this work we report on the structural properties of alkali hydrido-closo-(car)borates, a promising class of solid-state electrolyte materials, using high-pressure and temperature dependent X-ray diffraction experiments combined with DFT calculations. The mechanical properties are determined from pressure dependent diffraction studies and DFT calculations; the shear moduli appear to be very low for all studied compounds revealing their high malleability (that can be beneficial for the manufacturing and stable cycling of all-solid-state batteries). The thermo-diffraction experiments also reveal a high coefficient of thermal expansion for these materials. We discover a pressure induced phase transition for K2B12H12 from Fm-3 to Pnnm symmetry around 2GPa. A temperature induced phase transition for Li2B10H10 was also observed for the first time by thermodiffraction and the crystal structure solved combining experimental data and DFT calculations. Interestingly, all phases of the studied compounds (including newly discovered high pressure and high temperature phases) may related via group-subgroup relationship, with the notable exception of the room temperature phase of Li2B10H10