Insights into thermodynamic destabilization in Mg-In-D hydrogen storage system: A combined synchrotron X-ray and neutron diffraction study

Abstract

In this study, ultrafine Mg(In) solid-solution particles were successfully prepared through an arc plasma method and their deuterium uptake/release performances were systematically estimated with respect to the identically processed pure Mg particles. Thermodynamic destabilization and kinetic enhancement of Mg-In-D system were achieved simultaneously with lower deuterium ab/desorption enthalpies and decreased desorption temperatures. For the first time, an in-situ synchrotron X-ray diffraction (ISXRD) coupled with neutron powder diffraction (NPD) technique and density functional theory (DFT) calculations clearly substantiated that an indium diffusion-dominated phase transition is the driving force for the evolution from mixture of MgD2 and Mg-In intermetallic to Mg-based solid solution during the deuterium release (DR). The ISXRD results clarified the real-time phase transition from MgIn to Mg3In at 515 K and the interreaction of MgD2 and Mg3In at 640 K, by which the matrix could be destabilized to trigger an indium-diffusion governed DR reaction in deuteride. Moreover, with the aid of NPD experiment, the microstructure evolution of Mg-In-D system demonstrated the continuous diffusion of indium into Mg/MgD2 upon desorption. The solubilized indium in MgD2 effectively reduced the D-migration energy barrier and stabilized the lattice structure to restrain the constriction of Mg-D bonds, through which the noticeable improvement on both thermodynamic and kinetic performances of the Mg-In system was achieved. The combination of synchrotron X-ray and neutron diffraction offers a high-efficiency strategy to fathom the hydrogen discharging mechanism from the viewpoint of real-time phase transitions and crystalline structure evolutions.