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.