Hydrogen sorption by magnesium hydride (MgH2) is a promising method for hydrogen storage, however, the sorption/desorption kinetics require improvement. Catalysts such as transition metals and their alloys are widely used to accelerate these processes. High-entropy alloys (HEAs), consisting of several elements in equimolar or close to them concentrations, have unique properties, including high catalytic activity due to the cocktail effect and high defect density.
In this study, the catalytic activity of Al–Cu–Fe–Ni–Cr HES nanoparticles in the process of hydrogen sorption in MgH2 was investigated. HES nanoparticles were obtained by mechanical alloying followed by annealing. The structural and morphological characteristics of the nanoparticles were studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM).
Magnesium hydride (MgH2) is considered as a promising hydrogen storage material due to its availability and favorable characteristics, including high storage capacity and cost-effectiveness under mild operating conditions. However, despite these advantages, MgH2 has suboptimal thermodynamics and kinetics, which complicates its practical application. This paper investigates the improvement of hydrogen storage performance of MgH2 using catalysts based on high-entropy Al–Cu–Fe–Ni–Cr (HEA) alloy obtained by mechanical alloying.
It has been experimentally established that the addition of 5 wt.% HEA Al–Cu–Fe–Ni–Cr to MgH2 leads to a significant decrease in the initial desorption temperature from 425 °C to 180 °C. In addition, the catalyst demonstrates accelerated kinetics: hydrogen absorption reaches 7.3 wt.% in 3 minutes at 320 °C and a hydrogen pressure of 15 atm, and desorption is∼5 wt.% in 6 minutes at 320 °C. The data obtained indicate a significantly lower desorption temperature compared to other known catalysts. Over 25 cycles of MgH2, with the Al–Cu–Fe–Ni–Cr catalyst, HEA exhibits outstanding cyclic stability with minimal fluctuations (∼0.05 wt.%). Based on the detailed characterization of the materials, an effective catalytic mechanism for HEA is proposed taking into account the obtained results.
Addition of Al–Cu–Fe–Ni–Cr HES nanoparticles to MgH2 significantly improves the kinetics of hydrogen sorption/desorption. Temperature-programmed desorption (TPD) studies have shown a decrease in the temperature of hydrogen desorption from MgH2 containing HES nanoparticles. The improvement in kinetics is due to the catalytic effect of HES nanoparticles, which promote the dissociation of hydrogen molecules and facilitate the diffusion of hydrogen atoms in MgH2. The high catalytic activity of Al–Cu–Fe–Ni–Cr HES is due to the presence of multiple active centers on the surface of the nanoparticles and the synergistic effect of several elements.
Author: Yogesh Kumar Yadav, Mohammad Abu Shaz, Thakur Prasad Yadav
Institute:
Department of Physics, Institute of Sciences, Banaras University, Varanasi, 221005, Uttar Pradesh, India
Department of Physics, Faculty of Science, Allahabad University, Prayagraj 211002, Uttar Pradesh, India