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 (HEB) with electron traps was designed and fabricated via a facile reduction method to improve the hydrogen storage properties of magnesium hydride (MgH 2 ). For dehydrogenation, the onset temperature of MgH 2 + 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) to (65.04 ± 2.81) kJ/mol. In addition, MgH 2 + 10wt% HEB could absorb hydrogen at 21.5°C, and 5.02wt% H 2 was charged in 50 min at 75°C. For reversible hydrogen storage capacity tests, the composite maintained a retention rate of 97% with 6.47wt% 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 MgH 2 . Driven by the cocktail effect as well as the orbital hybridization of metal borides, numerous active sites steadily enhanced the hydrogen storage reactions in MgH 2 .
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