Enhanced hydrogen storage performance of magnesium hydride catalyzed by medium-entropy alloy CrCoNi nanosheets.

The sluggish de/hydrogenation kinetics and stable thermodynamics of magnesium hydride (MgH 2) are unfavorable for its large-scale application. Herein, the medium-entropy alloy CrCoNi nanosheets were synthesized and remarkably enhanced the low-temperature hydrogen storage performance of MgH 2. Surprisingly, the initial dehydrogenation temperature of 9 wt% CrCoNi modified MgH 2 was greatly reduced from 325 °C to 195 °C, a drop of 130 °C compared to non-additive MgH 2. Also, the MgH 2 –CrCoNi composite released 4.84 wt% hydrogen at 300 °C even in 5 min and absorbed 3.19 wt% hydrogen at 100 °C within 30 min (3.2 MPa). The calculated de/rehydrogenation activation energy were reduced by 45 and 55 kJ mol−1, respectively. Further cyclic kinetics investigation indicates that the 9 wt%-CrCoNi doped MgH 2 still presented good stability after 20 cycles, losing only 0.36 wt% hydrogen capacity. The XRD pattern validated that CrCoNi remained stable during the cyclic reaction process. Besides, the uniformly distributed CrCoNi nanosheets were in tight contact with the MgH 2 surface, providing abundant catalytic active sites and low-energy barrier diffusion channels. Under synergistic catalysis, the H atoms are rapidly absorbed and released across the Mg/MgH 2 interface, resulting in excellent kinetic properties. Briefly, this paper provides new references and inspirations to design efficient polymetallic catalysts for hydrogen storage materials. • CrCoNi nanosheets were prepared via a facile wet chemical ball milling method. • The de/hydrogenation performance of 9 wt% CrCoNi modified MgH 2 was greatly enhanced. • The synergistic effect of Cr, Co and Ni elements played a key role in the catalysis on MgH 2. [ABSTRACT FROM AUTHOR]