Hydrogen desorption in nanocrystalline MgH2 thin films at room temperature

Hydrogen desorption process of Pd-capped magnesium hydride thin films of different thicknesses was investigated. Decomposition of magnesium hydride into magnesium under air exposure is observed in all investigated films. During decomposition no novel crystalline phases are detected. Desorption process was qualitatively analysed and it was concluded that is thermodynamically driven controlled by a nucleation and growth or by an interphase controlled mechanism. Moreover, H-kinetics investigation of desorption process was carried out by thermal desorption spectroscopy. Decomposition of MgH2 films occurs at Td∼148°C and the process seems to be controlled by a bidimensional interphase mechanism with an activation energy of 135±20kJ/molH2. No significant influence of thickness and crystallite size on desorption temperature is observed and obtained activation energy is similar to that of milled bulk magnesium.