FeCoNiCrMo high entropy alloy nanosheets catalyzed magnesium hydride for solid-state hydrogen storage

The catalytic effect of FeCoNiCrMo high entropy alloy nanosheets on the hydrogen storage performance of magnesium hydride (MgH₂) was investigated for the first time in this paper. Experimental results demonstrated that 9wt% FeCoNiCrMo doped MgH₂ started to de-hydrogenate at 200°C and discharged up to 5.89wt% hydrogen within 60 min at 325°C. The fully dehydrogenated composite could absorb 3.23wt% hydrogen in 50 min at a temperature as low as 100°C. The calculated de/hydrogenation activation energy values decreased by 44.21%/55.22% compared with MgH₂, respectively. Moreover, the composite’s hydrogen capacity dropped only 0.28wt% after 20 cycles, demonstrating remarkable cycling stability. The microstructure analysis verified that the five elements, Fe, Co, Ni, Cr, and Mo, remained stable in the form of high entropy alloy during the cycling process, and synergistically serving as a catalytic union to boost the de/hydrogenation reactions of MgH₂. Besides, the FeCoNiCrMo nanosheets had close contact with MgH₂, providing numerous non-homogeneous activation sites and diffusion channels for the rapid transfer of hydrogen, thus obtaining a superior catalytic effect.