Molecular Dynamics Investigation into the Hydrogen Adsorption Mechanism of the Magnesium-Based Material 2Mg–Fe Mixture

Abstract

Mg 2 FeH 6 , a potential hydrogen storage medium with the largest volumetric hydrogen capacity known, is mostly obtained by reacting the 2Mg−Fe mixture with hydrogen through mechanical alloying methods. However, these mechanical alloying methods for generating Mg 2 FeH 6 are inconvenient in operation, and the mechanism of formation of Mg 2 FeH 6 behind these methods is not clear so far. In this study, through molecular dynamics simulations, the microscopic process of the chemical reaction between the 2Mg−Fe mixture and hydrogen to produce Mg 2 FeH 6 was investigated to clarify the mechanism of hydrogen adsorption by the 2Mg−Fe mixture. By analyzing the changes in bond energy and potential energy of the system, as well as the atomic trajectory, the breaking and re-formation of chemical bonds are clarified, which indicates the microscopic mechanism of hydrogen adsorption by the 2Mg−Fe mixture. In addition, the influences of temperature and pressure on the hydrogen adsorption process of the 2Mg−Fe mixture were studied. It was shown that increasing the pressure has a positive effect on the hydrogen storage capacity of the 2Mg−Fe mixture, while increasing temperature beyond 300 °C has little effect. Especially, the mass hydrogen storage capacity of the 2Mg−Fe mixture at 10 MPa and 400 °C was found to reach its theoretical hydrogen storage capacity of 5.5 wt %.

Potential Benefits, Challenges and Perspectives of Various Methods and Materials Used for Hydrogen Storage

“…The production mechanism of Mg 2 FeH 6 , a magnesium-based hydride, is not yet very clear; however, it has the potential to be a hydrogen storage medium with a 5.5 wt % hydrogen absorption capacity. Using modeling techniques, Yu et al have recently investigated the process of hydrogen adsorption at different pressures and temperatures, as well as the chemical reaction leading to the creation of Mg 2 FeH 6 . 5.5 wt % hydrogen absorption can only be achieved under the specified circumstances of 400 °C and 10 MPa of pressure, according to the research.…”

“…Using modeling techniques, Yu et al have recently investigated the process of hydrogen adsorption at different pressures and temperatures, as well as the chemical reaction leading to the creation of Mg 2 FeH 6 . 238 3), where M stands for an early transition metal element including Ti or Sc, A is for an element from group 13 or 14, like Al or Si, and X is for either C or N or their combinations. In MAX phases, the M−X bond outlasts the M−A bond, which is composed of ternary transition metal nitrides or carbides.…”