Dehydrogenation and reaction pathway of Perovskite-Type NH4Ca(BH4)3

Perovskite-type borohydride, NH4Ca(BH4)3, is considered as a promising hydrogen storage material due to its high gravimetric hydrogen capacity (15.7 wt%). In this work, the dehydrogenation performance and reaction pathway of NH4Ca(BH4)3 have been systematically investigated. It is found that the initial decomposition temperature is only 65 °C, suggesting a low thermodynamic stability of NH4Ca(BH4)3. The desorption kinetics conducted by differential scanning calorimetry (DSC) indicates that the activation energy of decomposition is about 226.1 kJ/mol. The dehydrogenation pathway of NH4Ca(BH4)3 characterized by fourier-transform infrared spectroscopy (FTIR) and solid-state nuclear magnetic resonance (NMR) shows a stepwise decomposition process, in which the initial dehydrogenation is due to destabilization of H+ in NH4 and H- in BH4 followed by the subsequent dehydrogenation steps arising from the decomposition of homologous NH3BH3 and the final decomposition of Ca(BH4)2 at a high temperature, respectively.