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Density functional theory calculations have been performed on a range of magnesium and magnesium hydride nanoclusters to examine the 1 bar desorption temperatures. The vibrational entropies and enthalpies are calculated for each cluster, within the harmonic approximation, which permits calculation of the desorption Gibbs free energy of reaction. For the bulk system, good agreement is found with experiment for the desorption temperature and a range of structural and electronic properties. For the nanoparticulate systems, we report binding energies, along with desorption reaction entropies and enthalpies. The finite-temperature effects on the vibrational energies of all system sizes are examined, and the findings suggest that the harmonic approximation is too restricted to account for the experimentally observed reductions in the nanoparticulate reaction enthalpies.

Li-ion batteries have held the dominant position in battery research for the last 30+ years. However, due to inadequate resources and the cost of necessary elements (e.g., lithium ore) in...

Metal dodecaborate salts have been identified as a new class of ion conductors that are highly tunable. A [B−H] unit within the dodecaborate anion can be replaced with a Pb atom to create a dipole and anisotropy within the anion to tune the crystal structure of alkali metal salts, enhancing ion conductivity for solid-state electrolyte (SSE) applications in batteries. Li 2 B 11 H 11 Pb•xH 2 O shows superionic conductivity up to ∼7 mS cm −1 at 120 °C, proving it comparable to state-of-the-art LiCB 11 H 12 at these temperatures. Dehydration of the Li salt occurs above 120 °C, causing changes in the crystal structure and a decrease in the ion conductivity. Na 2 B 11 H 11 Pb•xH 2 O shows modest ion conductivity (0.01 mS cm −1 at 170 °C), whereas the potassium salt shows conductivities below 1 × 10 −5 mS cm −1 . The B 11 H 11 Pb 2− analogues are proposed to be inferior ion conductors to the CB 11 H 12 − varieties due to the divalent B 11 H 11 Pb 2− anion causing stronger bonding between the cation and anion, possibly higher energy required to move from position to position within the crystal structure. Despite this, the insertion of a lead atom into the dodecaborate cage shows promise in allowing high ion conductivity in the solid state.

Thermodynamics of Hydrogen Desorption from NaMgH 3 and Its Application as a Solar Heat Storage Medium. -NaMgH3 is synthesized by cryomilling (77 K) of NaH and MgH2 followed by annealing at 300°C under 50 bar H2. Its thermodynamic properties and hysteresis are determined by kinetic desorption measurements for each data point of the pressure-composition isotherms. Both the decomposition enthalpy and entropy are lower than previously reported. Complete hydrogen desorption to metallic Na and Mg results in macroscopic segregation that kinetically hinders rehydrogenation to NaMgH3. Provided decomposition to Na metal is avoided, NaMgH3 is a potential solar heat storage material. -(SHEPPARD*, D. A.; PASKEVICIUS, M.; BUCKLEY, C. E.; Chem.