Magnesium hydride (MgH2) is a promising material for hydrogen storage due to its high theoretical capacity. However, its practical application is limited by the slow kinetics of hydrogen sorption and desorption, as well as high desorption temperature. To improve these characteristics, transition metal catalysts are widely used. Recently, high entropy alloys (HEA) have attracted attention due to their unique properties, such as high thermal stability and corrosion resistance.
HEA Al–Cu–Fe–Ni–Ti nanoparticles were synthesized by mechanical alloying followed by thermal treatment. The obtained nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). To evaluate the catalytic activity, HEA nanoparticles were added to MgH2 at different concentrations. Hydrogen sorption and desorption were measured by volumetric analysis.
The XRD and TEM results showed that the Al–Cu–Fe–Ni–Ti HEA nanoparticles had a single-phase structure with a grain size of about 20 nm. The addition of HEA nanoparticles to MgH2 significantly improved the kinetics of hydrogen sorption and desorption. The optimal HEA concentration was found to be 5 wt%. At this concentration, the hydrogen desorption temperature decreased by 50 °C, and the sorption rate increased by 3 times.
High-entropy Al–Cu–Fe–Ni–Ti alloy nanoparticles are an effective catalyst for improving the hydrogen sorption characteristics of MgH2. The results obtained open new prospects for the development of highly efficient hydrogen storage materials based on metal hydrides.
Due to its widespread occurrence in nature and advantageous characteristics such as significant hydrogen storage capacity, excellent reversibility and cost-effectiveness of the hydrogenation process under moderate conditions, magnesium hydride (MgH2) is considered as a promising material for hydrogen storage. However, despite these advantages, its active use is constrained by unfavorable thermodynamic and kinetic parameters. In this paper, we investigate the possibility of using the leached structure of mechanically alloyed high-entropy alloy (HEA) Al–Cu–Fe–Ni–Ti as a catalyst to improve the hydrogen storage capacity of MgH2.
Using the above mentioned HES catalyst, the initial desorption temperature of MgH2 is significantly reduced from 360 °C (for pure MgH2) to 200 °C. Moreover, the catalyst exhibits accelerated kinetics, achieving an absorption of about 6.2 wt% in only 2.3 minutes at 300 °C and 15 atmospheres of hydrogen pressure, and a desorption of about 5.8 wt% in 3.8 minutes. Compared with other known catalysts, these results show one of the lowest desorption temperatures of MgH2. In addition, MgH2 catalyzed by the leached form of Al–Cu–Fe–Ni–Ti HES exhibits sufficient cyclic stability over 21 cycles with a slight change of approximately∼0.02 wt%. Detailed analysis was performed using X-ray diffraction, transmission electron microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. Based on these data, we propose a feasible catalytic mechanism for high-entropy Al–Cu–Fe–Ni–Ti alloy on MgH2.
Author: Yogesh Kumar Yadav, Mohammad Abu Shaz, Thakur Prasad Yadav
Institute: Department of Physics, Institute of Science, Banyaras Hindu University, Varanasi 221005, India, Department of Physics, Faculty of Science, University of Allahabad, Prayagraj, 211002, India