Surprising cocktail effect in high entropy alloys on catalyzing magnesium hydride for solid-state hydrogen storage

Abstract

Magnesium hydride (MgH2) attracts wide interests as a promising hydrogen energy carrier, but its commercial application is hampered by the high operating temperatures and slow dehydrogenation kinetics. Herein, CrMnFeCoNi and CrFeCoNi high-entropy alloys (HEAs) were adopted to boost the hydrogen storage performance of MgH2. It was demonstrated that the morphology of catalysts and addition of Mn had a great impact on the performance of HEAs catalysts. In particular, the Mn containing HEAs nanosheets presented the best performance. The MgH2-CrMnFeCoNi composite could release 6.5 wt% H2 in 10 min at 300 °C and started to absorb H2 at 40 °C. Moreover, kinetic analysis revealed that the rate control model in dehydrogenation process of HEA-4 modified MgH2 changed from permeation model of MgH2 to diffusion. In addition, 97% hydrogen storage volume could be maintained after 20 cycles at 300 °C, showing a good cycling performance. Microstructure analysis showed that the CrMnFeCoNi nanosheets were uniform dispersed over the surface of MgH2, bringing numerous heterogeneous activation sites to speed up the dispersal of hydrogen. Besides, the cocktail effect of HEAs exerted synergic action between Cr, Mn, Fe, Co and Ni elements to improve the overall catalytic efficiency. Therefore, the de/rehydrogeantion performance of the MgH2-CrMnFeCoNi composite was surprisingly accelerated.