Amorphous scaly high-entropy borides with electron traps for efficient catalysis in solid-state hydrogen storage

Owing to the orbital hybridization between the transition metal and the B element and the electron-trapping effect of the B element, transition metal borides are considered very promising materials for energy catalysis. In this work, an amorphous scaly high-entropy boride with electron traps was designed and fabricated via a facile reduction method to improve the hydrogen storage properties of magnesium hydride (MgH2). For dehydrogenation, the onset temperature of MgH2 + 10wt% HEB was dropped to 187.4 C, besides, the composite exhibited superior isothermal kinetics and the activation energy of the composite was reduced from 212.78 ± 3.93 kJ/mol to 65.04 ± 2.81 kJ/mol. In addition, MgH2 + 10wt% HEB could absorb hydrogen at 21.5 ℃, and 5.02 wt% H2 was charged in 50 min at 75 ℃. For reversible hydrogen storage capacity tests, the composite maintained a retention rate of 97% with 6.47 wt% hydrogen capacity after 30 cycles. Combining microstructure evidence with hydrogen storage performance, the catalytic mechanism was proposed. During ball milling, scaly high-entropy borides riveted a large number of heterogeneous active sites on the surface of MgH2. Driven by the cocktail effect as well as the orbital hybridization of metal borides, numerous active sites steadily enhanced the hydrogen storage reactions in MgH2.