) 7.5 Compound Institute of Nuclear Technology and Radiation Protection, NCSR "Demokritos

Abstract The present research work is focused on the effect of activation procedure on the hydrogen absorption-desorption properties of new rare earth -transition metal compound based on Sm(Co 0.6 Fe 0.2 Zr 0.16 B 0.04 ) 7.5 composition. Crystal structure and composition is always connected to the maximum capacity of the intermetallic hydrides. For composite materials the thermodynamic properties of hydrogenation -dehydrogenation procedure are mostly explained through microstructuremicrochemistry characteristics. Efficient hydrogen storage is direct connected to the desorbed hydrogen amount. The as hydrogenated material Sm(Co 0.6 Fe 0.2 Zr 0.16 B 0.04 ) 7.5 seems to have in the desorption a pressure plateau below the atmospheric pressure at room temperature while the absorbed hydrogen almost remains in the material having capacity of ~0.8 wt. % at 0.1 MPa -30°C. After the proper activation procedure, the hydrogenated material desorbs very high amount of hydrogen ~1.9 wt. % at 0.1 MPa -100°C. Subsequently, the treatment of the composite materials before hydrogenation-dehydrogenation procedures could play a crucial role on the efficiency