Probing molecular dynamics of metal borohydrides on the surface of mesoporous scaffolds by multinuclear high resolution solid state NMR

Abstract

Understanding of surface interactions between borohydride molecules and the surfaces of porous supports have gained growing attention for successful development of nano-confinement engineering. By use of in␣situ variable temperature (VT) magic angle spinning (MAS) NMR, molecular mobility changes of LiBH_4 crystalline solid has been investigated in the presence of silica based and carbonaceous surfaces. Spin–spin J-coupling of ^(1)H–^(11)B in LiBH_4 was monitored in series of VT NMR spectra to probe translational mobility of LiBH_4 that appeared to be greatly enhanced upon surface contact. Such enhanced diffusivity was found to be effective in the formation of solid solution and co-confinement with other metal borohydrides. Co-confinement of LiBH_4–Ca(BH_4)_2 mixture was demonstrated at temperature as low as 100 °C, much lower than the reported bulk eutectic melting temperature. The discovery adds a novel property of LiBH_4 that has been proven to be highly versatile in many energy related applications.

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