New synthetic procedure for NaNH2(BH3)2 and evaluation of its hydrogen storage properties

Tremendous efforts have been devoted to the synthesis of new light element hydrides for hydrogen storage. Ammonia borane (AB) is a promising candidate possessing high hydrogen capacity and low dehydrogenation temperature. The step-wise dehydrogenation and release of by-products, however, are obstacles to its practical application. Chemical modifications of AB to synthesize new compounds or its derivatives are of practical and fundamental importance. Here we report an improved synthesis of sodium aminodiborane (NaNH2(BH3)2, NaABB), a derivative of ammonia borane. This procedure leads to high purity NaABB by reacting NaNH2 and 2 eq. AB. The dehydrogenation properties have been investigated by means of temperature programmed desorption-mass spectrometry, volumetric release, nuclear magnetic resonance, Fourier transform infrared spectroscopy, and X-ray diffraction. In a closed vessel, NaABB can release ~2 eq. H2 when heated at 271 °C, forming solid products of NaBH4 and highly condensed polyborazylene.