Hydrogen desorption studies of the Mg24Y5–H system: Formation of Mg tubes, kinetics and cycling effects

The current study focuses on the hydrogen desorption properties of hydrogenated Mg24Y5. Recently, we have reported the formation of unidirectional MgH2 structures by hydrogen absorption and induced disproportionation of Mg24Y5. During hydrogen desorption, a complex voiding phenomenon produces Mg tubes and carved particles with nano-sized walls. The selected area electron diffraction patterns demonstrate that the Mg tubes are single crystals. A harmonized picture of the unidirectional growth based on different Mg vapor models is proposed. The kinetic properties of hydrogen desorption are improved as compared with commercial MgH2. Hydrogenation/dehydrogenation cycling lowers the thermal stability of the hydrogen desorption at the expense of the total desorbed hydrogen capacity. Both whiskers and microparticles are depleted into clusters of nanoparticles after extensive cycling.