Improved reversible dehydrogenation properties of Mg(BH4)2 catalyzed by dual-cation transition metal fluorides K2TiF6 and K2NbF7

Two dual-cation transition metal fluorides K 2 TiF 6 and K 2 NbF 7 are introduced into Mg(BH 4 ) 2 by ball-milling to catalyze the dehydrogenation of Mg(BH 4 ) 2 . According to the DSC and TPD results, the onset dehydrogenation temperature of Mg(BH 4 ) 2 doped with K 2 TiF 6 and K 2 NbF 7 are remarkably reduced to 105.4 and 118.0 °C, respectively. Meanwhile, both the K 2 TiF 6 and K 2 NbF 7 catalyzed systems can release more than 6.4 wt% H 2 under 280 °C, showing an improvement in dehydrogenation kinetics. In addition, the reversible capacity of the Mg(BH 4 ) 2 –3%K 2 TiF 6 system is 2.7 wt% at 280 °C in 250 min, which is enhanced comparing to that of pristine Mg(BH 4 ) 2 . X-ray diffraction, Fourier-transformed infrared and 11 B nuclear magnetic resonance investigations reveal that the K 2 TiF 6 actually acts as a catalytic precursor to react with Mg(BH 4 ) 2 , forming active hydrides of KBH 4 and TiH 2 , which further serve as catalyzing agents to facilitate the re-generation of Mg(BH 4 ) 2 from intermediates under moderate conditions.