Destabilizing the Dehydrogenation Thermodynamics of Magnesium Hydride by Utilizing the Immiscibility of Mn with Mg

Hydrogen storage is a key technology for the advancement of hydrogen and fuel cell power technologies in stationary and portable applications. MgH2, an example of a high-capacity hydrogen storage material, has two major material challenges for practical applications: slow hydrogen desorption kinetics and high hydrogen desorption temperature. Numerous studies have reported enhancements in kinetics but only a few in thermodynamics. Here, we present a simple but effective way to improve upon both the kinetic and thermodynamic aspects of desorption by utilizing the immiscibility of Mn, a non-hydrogen absorbing metal, with Mg. Mg0.25Mn0.75, prepared through ball milling MgH2 and Mn powders, is a nanocomposite where the nanometer-sized MgH2 domains are randomly embedded in a Mn matrix. This sample readily and reversibly absorbs and desorbs deuterium even at a temperature of 200 °C without the addition of any catalysts. This is nearly 180 °C lower than the typical operating temperature of conventional bulk Mg. F...