Al–Cu–Fe–Ni–Ti high entropy alloy nanoparticles as new catalyst for hydrogen sorption in MgH2

Abstract

The earth's abundance of magnesium hydride (MgH<inf>2</inf>), along with its favorable qualities like high capacity, excellent reversibility, and cost-effectiveness under mild hydrogenation conditions, make it a potential material for hydrogen storage. Its practical applicability is limited by unfavorable thermodynamics and kinetics, despite these advantages. In this work, we investigate the use of a leached form of the mechanically alloyed high entropy alloy (HEA) Al–Cu–Fe–Ni–Ti as a catalyst to improve the hydrogen storage capabilities of MgH<inf>2</inf>. The onset desorption temperature of MgH<inf>2</inf> is significantly reduced from 360 °C (for as-received MgH<inf>2</inf>) to 200 °C when catalyzed by the previously stated HEA catalyst. In addition, the catalyst exhibits enhanced kinetics, as it can absorb around 6.2 wt. % in just 2.3 min. at 300 °C and 15 atm of hydrogen pressure, and desorb approximately 5.8 wt. % in 3.8 min. When compared to other known catalysts, these results show some of the lowest desorption temperatures for MgH<inf>2</inf>. Furthermore, MgH<inf>2</inf> catalyzed by the leached form of Al–Cu–Fe–Ni–Ti HEA exhibits good cyclic stability for up to 21 cycles, with just a small variation of about ∼0.02 wt. %. A thorough analysis using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy have been carried out. We suggest a workable catalytic mechanism for the high entropy alloy Al–Cu–Fe–Ni–Ti on MgH<inf>2</inf> based on these findings. © 2024 Hydrogen Energy Publications LLC