Fully Reversible De/hydriding of Mg Base Solid Solutions with Reduced Reaction Enthalpy and Enhanced Kinetics

Abstract

This paper presents a new approach to tune the de/hydriding thermodynamic properties of Mg via forming reversible Mg base solid solutions in the Mg−In and Mg−In−Al systems by mechanical milling. The effect of solubility of In and Al on the reversible formation of solid solution structure and hydrogen storage properties were investigated. It is found that although the solute atoms unavoidably are rejected upon hydriding, the hydrogenated products of MgH 2 and intermediate MgIn compound could fully transform back to solid solution after dehydrogenation. In the hydriding of Mg(In, Al) ternary solid solution, Al would get dissolved into MgIn compound rather than forming free Al like the Mg(Al) binary solid solution. Therefore, the presence of In improves the dehydriding reversibility of Mg(Al) solid solution, and the reversible Al concentration could be increased up to the 8 at. %, which is just the solubility limit of Al in Mg by mechanical milling. The reversible phase transformation is responsible for the reduction in the desorption enthalpy of MgH 2 , being 12 kJ/(mol•H 2 ) reduction for the alloy Mg 0.9 In 0.1 relative to the desorption enthalpy of pure MgH 2 . Further, the hydrogen sorption kinetics of Mg(In) solid solutions are enhanced. Comparatively, both the thermodynamic destabilizing effect and the kinetic enhancing effect due to the Al dissolving are inferior to those due to the In dissolving. This work demonstrates a feasible way to improve the thermodynamics and kinetics of Mg base hydrogen storage alloys through traditional metallurgical method.

Enhanced joint catalysis of YH2/Y2O3 on dehydrogenation of MgH2

“…The fitting results show that all g values at different temperatures are close to 3, suggesting that the dehydrogenation of the MgH 2 -YH 2 composite follows three dimensional growth model. The E a for dehydrogenation is determined to be 139 kJ/mol, lower than the value $160 kJ/mol for pure MgH 2 [19]. The determined E a for hydrogen desorption is rather close to that (137 kJ/mol) for 20 h-milled Mg + 10 wt.%Y composite reported in Ref.…”

Recent advances on the thermal destabilization of Mg-based hydrogen storage materials

“…Compared with the binary Mg (Al) solid solution, the Mg (In, Al) ternary solid solution presented improved dehydriding reversibility and a substantial decrease in DH because Al was dissolved in the b phase. 45 With respect to the Mg-In-Y ternary system, the reversible dissolving of Y in Mg was realized by the decomposition of the In 3 Y phase in dehydriding, but the reversible solubility of Y is rather low due to the formation of YH 2 . The Mg 90 In 5 Y 5 solid solution exhibited a decreased reaction enthalpy of 62.9 kJ (mol À1 H 2 ), which was reduced by 5 kJ (mol À1 H 2 ) and 12 kJ (mol À1 H 2 ) compared to that of the Mg 95 In 5 binary solid solution and pure Mg, respectively.…”

Mechanism of Thermodynamic Destabilization and Fast Desorption Kinetics in a Mechanically Alloyed MgH2–In Composite

“…12-0697) are drastically broadened due to its nearly amorphous nanoscale structure. 16 25 The formation of MgIn phase was not detected by the selected area electron diffraction (SAED) analysis; this is probably due to its minor quantity. The HRTEM images (Figure 2d,e), fast Fourier 3a).…”