Mechanochemical synthesis of hydrogen-storage materials based on aluminum, magnesium and their compounds

Over the last few decades, interest in hydrogen-storage materials as an alternative high-efficiency and safe, green energy carriers is steadily increasing. Among numerous hydrides scrutinized for the purpose over the past 10-15 years, aluminum- and magnesium-based systems attract continued attention, mainly because of their high gravimetric capacity and low cost. However, difficulties associated with facile synthesis and hence the reversibility, relatively high desorption temperatures, and sluggish kinetics in many of these systems are still of great concern and hold them back from broad, large-scale applications, e.g. in automotive industry. Our research was devoted to studies of mechanochemical activation and synthesis of nanostructured hydride systems of aluminum and magnesium by solid-state mechanical milling techniques. The structural and desorption properties of milled powders were examined by powder X-ray diffraction (XRD), solid-state nuclear magnetic resonance (NMR) spectroscopy and desorption analysis in a Sieverts-type apparatus. The primary focus of this study was to investigate a number of aluminum-based hydride systems to develop advanced synthesis procedures for AlH3 (alane) using solvent-free solid-state mechanical milling under moderate hydrogen pressures at room temperature. The findings reported in this dissertation, may provide the much needed basic scientific insight necessary for the development of an approach for direct mechanochemical hydrogenation of metallic aluminum which still remains elusive despite numerous efforts worldwide. Here, we have demonstrated a mechanochemical approach for synthesis of alane via metathesis reactions between hydride sources and aluminum halides. Reaction pathways and parameters controlling the reactions were investigated. Additionally, the possibility of mechanochemical hydrogenation of magnesium boride (MgB2) was also studied

A Benign Synthesis of Alane by the Composition-Controlled Mechanochemical Reaction of Sodium Hydride and Aluminum Chloride

Solid-state mechanochemical synthesis of alane (AlH3) starting from sodium hydride (NaH) and aluminum chloride (AlCl3) has been achieved at room temperature. The transformation pathway of this solid-state reaction was controlled by a step-wise addition of AlCl3 to the initial reaction mixture that contained sodium hydride in excess of stoichiometric amount. As in the case of previously investigated LiH-AlCl3 system, complete selectivity was achieved whereby formation of unwanted elemental aluminum was fully suppressed, and AlH3 was obtained in quantitative yield. Reaction progress during each step was investigated by means of solid-state NMR and powder X-ray diffraction, which revealed that the overall reaction proceeds through a series of intermediate alanates that may be partially chlorinated. The NaH-AlCl3 system present some subtle differences compared to LiH-AlCl3 system particularly with respect to optimal concentrations needed during one of the reaction stages. Based on the results we postulate that high local concentrations of NaH may stabilize chlorine-containing derivatives and prevent decomposition into elemental aluminum with hydrogen evolution. Complete conversion with quantitative yield of alane was confirmed both by SSNMR and hydrogen desorption analysis

Luminescence properties of mechanochemically synthesized lanthanide containing MIL-78 MOFs

Three metal–organic framework (MOF) compounds, Ln0.5Gd0.5{C6H3(COO)3}; Ln = Eu, Tb, and Dy with a MIL-78 structure, have been synthesized by a solvent-free mechanochemical method from stoichiometric mixtures of benzene 1,3,5-tricarboxylic acid, C6H3(COOH)3, also known as trimesic acid, and the respective lanthanide carbonates, Ln2(CO3)3·xH2O, Ln = Eu, Gd, Tb and Dy. MIL-78 (Ln0.5Gd0.5) shows the characteristic red, green, and yellow luminescence of Eu3+, Tb3+, and Dy3+, respectively. Efficient intramolecular energy transfer from the ligand triplet state to the excited states of Ln3+ ions can be observed. The lifetimes and quantum yields of these compounds are studied and discussed in detail. Among the three compounds, the Tb3+ containing compound shows the longest lifetime and highest quantum yield due to a smaller contribution from non-radiative decay pathways and better matching of the lowest triplet energy level of the benzenetricarboxylate ligand and the resonance level of Tb3+

Mechanochemical recovery of Co and Li from LCO cathode of lithium-ion battery

Increasing demand for lithium-ion batteries (LIBs) that serve as power source for diverse electronic devices, electrical propulsion systems and other applications, calls for economical and environmentally benign recycling of spent LIBs and recovery of critical elements such as Co and Li from rapidly growing volumes of battery wastes. The presented study explores mechanochemical extraction of Co and Li from lithium cobaltate (LiCoO2), which serves as cathode material in commercial LIBs. Our investigation reveals that solvent-free mechanochemical processing can successfully convert pure, reagent grade LiCoO2 into metallic Co and Li-derivatives that are suitable for the further recovery of Li. We also show that the proposed approach can be successfully applied to reclaiming these critical elements from commercial LIBs. Due to its magnetic nature, metallic Co is easy to separate from non-magnetic components of mechanochemically generated powder mixtures using an appropriate magnetic separation technique, while Li can be reclaimed as Li2CO3 after an additional liquid-phase processing. The recovery rates achieved during our experiments with pure LiCoO2 are ∼90% for Co and ∼70% for Li

Depolymerization of polystyrene under ambient conditions

Depolymerization of the addition polymer polystyrene to monomeric styrene is facilitated by mechanochemical processing at room temperature under ambient atmosphere. The reaction occurs in metal-based milling media in concert with scission of macromolecular chains that generates carbon-centered free-radicals detectable by EPR spectroscopy, even though the processing is performed in air.This article is published as Balema, Viktor P., Ihor Z. Hlova, Scott L. Carnahan, Mastooreh Seyedi, Oleksandr Dolotko, Aaron J. Rossini, and Igor Luzinov. "Depolymerization of polystyrene under ambient conditions." New Journal of Chemistry 45, no. 6 (2021): 2935-2938. DOI: 10.1039/D0NJ05984F. Copyright 2021 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique. Posted with permission

Unusual first-order magnetic phase transition and large magnetocaloric effect in Nd2In

A large magnetocaloric effect with its maximum near the boiling point of natural gas occurs in a rare-earth intermetallic compound Nd2In. While behaviors of physical properties indicate that paramagnetic-ferromagnetic transformation supporting the large magnetocaloric effect is first order in nature, temperature-dependent crys-tallographic study reveals no changes in lattice symmetry and lack of discontinuities either in phase volume or lattice parameters. The borderline first-order nature of phase transformation in Nd2In is markedly different from conventional first-order magnetic transitions occurring in other members of the family - isostructural Pr2In and nonisostructural Eu2In.This article is published as Biswas, Anis, Rajiv K. Chouhan, Alex Thayer, Yaroslav Mudryk, Ihor Z. Hlova, Oleksandr Dolotko, and Vitalij K. Pecharsky. "Unusual first-order magnetic phase transition and large magnetocaloric effect in Nd 2 In." Physical Review Materials 6, no. 11 (2022): 114406. DOI: 10.1103/PhysRevMaterials.6.114406. Copyright 2022 American Physical Society. Posted with permission. DOE Contract Number(s): AC02-07CH1135

Solid-State NMR Study of Li-Assisted Dehydrogenation of Ammonia Borane

The mechanism of thermochemical dehydrogenation of the 1:3 mixture of Li₃AlH₆ and NH₃BH₃ (AB) has been studied by the extensive use of solid-state NMR spectroscopy and theoretical calculations. The activation energy for the dehydrogenation is estimated to be 110 kJ mol^–1, which is lower than for pristine AB (184 kJ mol^–1). The major hydrogen release from the mixture occurs at 60 and 72 °C, which compares favorably with pristine AB and related hydrogen storage materials, such as lithium amidoborane (LiNH₂BH₃, LiAB). The NMR studies suggest that Li₃AlH₆ improves the dehydrogenation kinetics of AB by forming an intermediate compound (LiAB)_<i>x</i>(AB)_1–<i>x</i>. A part of AB in the mixture transforms into LiAB to form this intermediate, which accelerates the subsequent formation of branched polyaminoborane species and further release of hydrogen. The detailed reaction mechanism, in particular the role of lithium, revealed in the present study highlights new opportunities for using ammonia borane and its derivatives as hydrogen storage materials

Unprecedented generation of 3D heterostructures by mechanochemical disassembly and re-ordering of incommensurate metal chalcogenides

3D heterostructures offer properties that are inaccessible in bulk single-phase solids, but synthetic approaches are limited. The authors use mechanochemical reshuffling of binary precursors and subsequent annealing to design structurally aligned misfit heterostructures with well-defined atomic arrangements