Abstract

In the present work we report the desorption pathway of the 2NaBH₄ + MgH₂ system. Ex-situ X-ray powder diffraction (XRPD) and solid state magic angle spinning (MAS) nuclear magnetic resonance (NMR) measurements have been performed on samples heat treated up to 450 °C for different times. Ex-situ X-ray powder diffraction experiments conducted on fully desorbed samples allowed us to identify nanocrystalline MgB₂ and metallic Na as dehydrogenation products. ¹¹B and ²³Na NMR analyses have been also carried out in order to evaluate the structural evolution of decomposed materials. Our measurements show that the local structure of MgB₂ is influenced by replacement of Mg with Na atoms in the Mg sites. Moreover, amorphous Na₂[B₁₂H₁₂] was detected in the partially desorbed sample and in the final products of the decomposition reaction. The presence of the [B₁₂H₁₂]^2– anion was confirmed by both direct comparison with the ¹¹B{¹H} NMR spectrum of pure Na₂[B₁₂H₁₂] and dynamic cross-polarization experiments.

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