Synthesis and advanced dehydrogenation properties of niobium-based ammine borohydride

In this paper, niobium-based ammine borohydride has been synthesized via a simple ball milling of NbCl5·5NH3 and MBH4 (M = Li, Na) with a molar ratio of 1:5. Thermogravimetric analysis-mass spectrometry (TGA-MS) and temperature-programmed-desorption (TPD) results revealed that the dehydrogenation of NbCl5·5NH3/5LiBH4 and NbCl5·5NH3/5NaBH4 mixtures showed a two-step decomposition process with a total of 8.1 wt.% and 11.2 wt.% pure hydrogen evolution upon heating to 250 °C, respectively. Isothermal TPD results showed that over 6 wt.% and 10.4 wt.% pure hydrogen were liberated from NbCl5·5NH3/5NaBH4 within 60 min at 150 °C and 220 °C, respectively. Fourier transform infrared spectroscopy (FTIR) and isotope tagging measurements demonstrated that the dehydrogenation mechanism of niobium-based ammine borohydride is not only based on the combination reaction of BH and NH groups, but the BH⋯HB and NH⋯HN homo-polar interactions also contribute to the H2 formation.