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BH4− self-diffusion in liquid LiBH4.

The journal of physical chemistry. A (2010-09-03)
Pascal Martelli, Arndt Remhof, Andreas Borgschulte, Philippe Mauron, Dirk Wallacher, Ewout Kemner, Margarita Russina, Flavio Pendolino, Andreas Züttel
ABSTRACT

The hydrogen dynamics in solid and in liquid LiBH4 was studied by means of incoherent quasielastic neutron scattering. Rotational jump diffusion of the BH4- subunits on the picosecond scale was observed in solid LiBH4. The characteristic time constant is significantly shortened when the system transforms from the low-temperature phase to the high-temperature phase at 383 K. In the molten phase of LiBH4 above 553 K, translational diffusion of the BH4- units is found. The measured diffusion coefficients are in the 10(-5)cm2/s range at temperatures around 700 K, which is in the same order of magnitude as the self-diffusion of liquid lithium or the diffusion of ions in molten alkali halides. The temperature dependence of the diffusion coefficient shows an Arrhenius behavior, with an activation energy of Ea = 88 meV and a prefactor of D0 = 3.1 × 10(-4)cm2/s.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Lithium borohydride, ≥95.0%
Sigma-Aldrich
Lithium borohydride, ≥90%
Sigma-Aldrich
Lithium borohydride, hydrogen-storage grade, ≥90%
Sigma-Aldrich
Lithium borohydride solution, 2.0 M in THF
Sigma-Aldrich
Lithium borohydride solution, 0.5 M in diethyl ether