Thermodynamic and Kinetic Destabilization of Mg Solid Solution Alloys with Nanosized grains for Hydrogen Storage

Solid solution magnesium-based alloys have garnered significant attention for hydrogen storage applications, yet their practical implementation has been constrained by their stable thermodynamic properties and sluggish kinetics. To resolve it, herein we report a novel nano-engineering approach to simultaneously enhance the kinetic and thermodynamic properties of Mg-based solid solution alloys. Using Mg(In) alloys as a model system, we demonstrate this positive size effect through a two-step fabrication process: first, Mg0.9In0.1 alloy was synthesized via ball-milling combined with absorption/desorption cycles. And subsequently the alloy was subjected to high-pressure milling upon 4 MPa H2 atmosphere with immiscible Mn at a controlled molar ratio, resulting in Mg(In) nanograins uniformly embedded within a Mn-composite matrix (denoted as (Mg0.9In0.1)xMn1-x). The novel (Mg0.9In0.1)0.25Mn0.75 nanocomposite with an average grain size of ~61 nm demonstrates superior hydrogen storage properties. Compared to pure MgH2, this material shows much lower onset and peak temperature for hydrogen release at ~120 and ~240 ℃, respectively. Moreover, their enhanced kinetic performance with much smaller activation energy of ~78.34 kJ/mol and better cycling stability with retention of 97% after 50th cycles are also obtained due to these Mg(In) nanograins with being kept well even upon multiple-cycling. This study highlights that the synergistic combination of solid solution formation and nanoscale engineering can effectively modify the thermodynamic and kinetic properties of magnesium-based hydrogen storage alloys, which offers a promising approach for developing high-performance magnesium alloy hydrogen storage materials.