Zebra-Striped Fibers in Relation to the H2 Sorption Properties for MgH2 Nanofibers Produced by a Vapor–Solid Process

Abstract

MgH2 is a promising candidate for solid-state H2 storage applications. To improve the H2 sorption kinetics, highly pure MgH2 nanofibers were synthesized by a vapor–solid process. The fibers showed improved sorption kinetics compared with bulk MgH2, which were investigated by a volumetric pressure–composition–temperature method. To choose a meaningful kinetic model that represented the physical reality and intrinsic kinetic parameters for the unique fiber structure, theoretical modeling of the sorption data and metallographic examinations of the in situ dehydrogenation process and partially hydrogenated samples were carried out. The Johnson–Mehl–Avrami (JMA) model, which is based on the theory of nucleation and growth transformation, was selected for the kinetic mechanism analysis of the hydrogenation/dehydrogenation of the fibers. The theoretical modeling by the JMA model indicated that the phase transformation of Mg to MgH2 (or of MgH2 to Mg) in the individual fibers proceeded one-dimensionally along the...