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Crystal Structures and Energy Storage Properties of Ammine Sodium Decahydro-closo-decaboranes (Na2B10H10·nNH3, n = 1, 2)

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journal contribution
posted on 2019-08-13, 19:33 authored by Mathias Jørgensen, Bjarne R. S. Hansen, Young-Su Lee, Young Whan Cho, Torben R. Jensen
Metal closo-boranes show remarkable thermal and chemical stabilities, making them appealing candidates for a wide range of applications, such as electrolytes in electrochemical batteries and ammonia storage for indirect hydrogen storage. Furthermore, owing to the large size and nonspherical geometry of the anion (e.g., B10H102– or B12H122–), metal closo-boranes display a rich structural diversity and thermal polymorphism. Here, we present the synthesis, characterization, and structural determination of the ammoniated metal closo-boranes, Na2B10H10·nNH3 (n = 1, 2). The thermal decomposition of Na2B10H10·2NH3 was investigated with synchrotron radiation in situ powder X-ray diffraction and simultaneous thermogravimetric analysis, differential scanning calorimetry, and mass spectrometry, revealing a reversible ammonia storage capacity of 15 wt % below 150 °C. Additionally, ionic conductivities of 2.7 × 10–8 (RT) and 4.7 × 10–8 S/cm (30 °C) for Na2B10H10·2NH3 and Na2B10H10·NH3, respectively, were measured with electrochemical impedance spectroscopy. A lower Na+ conductivity compared to the parent compound, Na2B10H10, is explained by an anchoring effect of ammonia in the rigid framework of the B10H102–-anions.