Size and stress dependent hydrogen desorption in metastable Mg hydride films

Abstract Mg is a promising light-weight material that has superior hydrogen storage capacity. However H 2 storage in Mg typically requires high temperature, ∼500–600 K. Furthermore it has been shown that there is a peculiar film thickness effect on H 2 sorption in Mg films, that is thinner Mg films desorb H 2 at higher temperature [1] . In this study we show that the morphology of DC magnetron sputtered Mg thin films on rigid SiO 2 substrate varied from a continuous dense morphology to porous columnar structure when they grew thicker. Sputtered Mg films absorbed H 2 at 373 K and evolved into a metastable orthorhombic Mg hydride phase. Thermal desorption spectroscopy studies show that thinner dense MgH 2 films desorb H 2 at lower temperature than thicker porous MgH 2 films. Meanwhile MgH 2 pillars with greater porosity have degraded hydrogen sorption performance contradictory to general wisdom. The influences of stress on formation of metastable MgH 2 phase and consequent reduction of H 2 sorption temperature are discussed.