Dual-cation K2TaF7 catalyst improves high-capacity hydrogen storage behavior of MgH2

Abstract

MgH2 has been extensively regarded as a low-cost hydrogen storage material with high gravimetric hydrogen capacity of approximately 7.6 wt%. However, the hydrogen release and absorption kinetics in MgH2 still needs further improving. For the first time, the catalytic impacts of a new dual-cation metal fluoride K2TaF7 upon the hydrogen storage characteristics of MgH2 have been investigated in this work. With only 1 wt% K2TaF7 dopant, the initial dehydrogenation temperature of MgH2 was lowered by about 130 °C, releasing more than 7.3 wt% hydrogen totally. The desorption activation energy of MgH2 + 1 wt% K2TaF7 composite was decreased to 107.2 ± 1.2 kJ mol−1. Besides, at 190 °C, the dehydrogenated MgH2 + 1 wt% K2TaF7 sample could absorb 6.56 wt% H2, while pristine MgH2 re-absorbed only 3.45 wt% H2. Further studies revealed that K2TaF7 could react with MgH2 during dehydrogenation and produce symbiotic hydrides KMgH3 and TaH0.8, which could play the role of hydrogen pumps during hydrogen release and uptake. The cooperative catalysis between the hydrogen pump effect and the active interface in the multi-hydride area significantly enhanced the reversible hydrogen storage in the MgH2+1 wt% K2TaF7 composite. This study provides new thinking for novel catalysts to elevate the hydrogen storage performance of MgH2.