HYDROGEN STORAGE CHARACTERISTICS AND CYCLING STABILITY OF NANOSTRUCTURED MgH2-Cr_2O_3 COMPOSITE

摘要

This paper presents investigations on the long-term cycling stability as well as thehydriding/dehydriding properties of nanostructured MgH2 with 0.2 mole% Cr2O3 catalystadditions synthesized by ball milling. The hydrogen charge and discharge stability of thenan°Composite hydride has been tested at 300°C for up to 1000 cycles. Between the firstand the 500th or 1000th cycle, an increase of hydrogen storage capacity by about 8% isobserved in dynamic and PCT measurements. This is attributed to structural relaxationsand crystallite growth. While absorption kinetics remain almost as fast as in the first cycle,the kinetics curves show a significant and systematic slow-down of the desorption rates byabout a factor of four. Evaluation of X-ray patterns before and after 1000 cycles revealscrystallite growth from initially 21 nm to 84 nm after 1000 cycles. This microstructuralcoarsening during cycling may explain the decreasing desorption rate of thenan°Crystalline magnesium based composite.