Nanobubbles (NBs) are nanoscopic gaseous domains than can exist on solid surfaces or in bulk liquids. They have attracted substantial attention due to their long-time (meta)stability and a high potential for real-world applications. Using an approach not previously investigated, we exploit surface-electrostatic NB formation and stabilization via application of external electric fields in gas-liquid systems, with the marked result of massively increased gas uptake into the liquid in NB form. The de facto gas solubility enhancement (over many months) ranges from 2.5-fold for oxygen to 30-fold for methane vis-à-vis respective Henry’s law values for gas solubility; the more hydrophobic the gas, the more spectacular the increase. Molecular dynamics simulations reveal that the origin of NBs’ movement lies in dielectrophoresis, while substantial NB stabilization arises from a surface-polarization interaction.
Monoclinic α-Nb2O5 was chemically lithiated by reaction with n-butyllithium, mimicking the product of electrochemical discharge of a niobium oxide cathode vs. a Li anode. The compound was investigated by neutron powder diffraction (D2B equipment at ILL, France) and its structure was Rietveld refined in space group P2 to wRp = 0.045, locating the Li atoms inserted in the α-Nb2O5 framework. The ensuing chemical formula is Li12/7Nb2O5. Some Li atoms are more strongly bonded (five coordinated O atoms), some are less strongly bonded (coordination number = 4). Starting from the experimental structure, first-principles periodic DFT calculations based on the hybrid B3LYP functional were performed. The electrochemical voltage of Li insertion was computed to be 1.67 V, fully consistent with the experimental 1.60 V plateau vs. capacity. The analysis of the electron band structure shows that lithiation changes the insulating oxide into a semi-metal; some of the extra electrons inserted with lithium become spin-polarized and give the material weak ferromagnetic properties.
Joint decomposition of hydrides may be energetically favored, if stable mixed compounds are formed. This 'hydride destabilization' improves the energetics of H2 release from hydrogen storage materials. The sequence of dehydrogenation reactions of the 2LiBH4-Mg2FeH6 composite was studied by PCI (Pressure-Composition-Isotherm) and TPD (Temperature-Programmed-Desorption) techniques in a Sievert apparatus. Produced phases were identified by ex-situ X-ray diffraction and FTIR spectroscopy. Three distinct plateaus are detected on each isotherm: A, B, and C on decreasing pressure. The A reaction, involving formation of FeB, MgH2 and LiH, occurs at higher pressure/lower temperature than dehydrogenation of either pure hydrides; these are then effectively destabilized thermodynamically. The B process is plain decomposition of MgH2, and in C the magnesium produced reacts with LiBH4 left forming MgB2 and LiH. The B+C sequence is fully reversible, and it corresponds to twostep dehydrogenation of the LiBH4/MgH2 system. Reaction enthalpies and entropies were obtained through van't Hoff plots of all processes, thus providing a full thermodynamic characterization of the system.
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