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

Graphical abstract: In situ variable temperature multinuclear solid state NMR allows to probe surface wetting, diffusivity, and confinement of metal borohydrides into nanopores. - 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 LiBH₄ crystalline solid has been investigated in the presence of silica based and carbonaceous surfaces. Spin–spin J-coupling of ¹H–¹¹B in LiBH₄ was monitored in series of VT NMR spectra to probe translational mobility of LiBH₄ 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 LiBH₄–Ca(BH₄)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 LiBH₄ that has been proven to be highly versatile in many energy related applications