Insights from impedance spectroscopy into the mechanism of thermal decomposition of M(NH2BH3), M = H, Li, Na, Li0.5Na0.5, hydrogen storesThis work celebrates the 220th birth anniversary of Michael Faraday.Electronic supplementary information (ESI) available: XRD patterns, FTIR and MAS 11B and 1H NMR spectra, and TGADSCEGA data. See DOI: 10.1039/c2cp23344d

We report the first solid-state impedance study of hydrogen-rich ammonia borane, AB, and its three alkali metal amidoborane derivatives. Temperature-dependent impedance spectra of solid M(NH 2 BH 3 ) salts are predominated by ionic conductivity, which at room temperature ranges from 5.5 S cm 1 (M = Li) to 2.23.0 mS cm 1 (Na, Na 0.5 Li 0.5 ), while the activation energy for conductivity is rather high (140158 kJ mol 1 ). Variation of conductivity with time can be used to extract information about the evolution of the system during thermal decomposition. By using a combination of impedance spectroscopy, thermogravimetric analysis, scanning calorimetry, evolved gas analysis, infrared absorption spectroscopy as well as 11 B and 1 H MAS NMR, we were able to reconfirm the complex pathway of thermal decomposition of amidoboranes postulated by two of us earlier ( J. Mater. Chem. 2009, 19 , 2043). Impedance spectroscopy study reveals electronic properties of alkali metal amidoboranes and transformation to ionically conducting phase preceding thermal decomposition.