Dehydriding reaction kinetic mechanism of MgH2-Nb2O5 by Chou model
(1. Shanghai Key Laboratory of Modern Metallurgy and Materials Processing, Shanghai University, Shanghai 200072, China;2. School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China)
Abstract: Chou model was used to investigate the dehydriding reaction kinetic mechanism of MgH2-Nb2O5 hydrogen storage materials at 573 K. A new conception, “characteristic absorption/desorption time (tc)” was introduced to characterize the reaction rate. The fitting results show that for the hydrogen desorbing mechanism, the surface penetration is the rate-controlling step. The mechanism remains the same even when the original particle size of Nb2O5 is before ball milling (BM) or when the BM time changes. And tc indicates that the desorption rate of MgH2-Nb2O5 will be faster than that of MgH2-Nb2O5 by BM. The dehydriding reaction rate of MgH2-Nb2O5 (micro particle) BMed for 50 h is 4.76 times faster than that of the MgH2-Nb2O5 (micro particle) BMed for 0.25 h, while the dehydriding reaction rate of MgH2-Nb2O5 (nano particle) BMed for 50 h is only 1.18 times as that of the MgH2-Nb2O5 (nano particle) BMed for 0.25 h. The dehydriding reaction rate of the BMed MgH2-Nb2O5 (nano particle) is 1-9 times faster than that of the BMed MgH2-Nb2O5 (micro particle).
Key words: MgH2 composite; Chou model; hydrogen desorbing mechanism