Article pubs.acs.org/JPCC
Kinetic Enhancement in the Sorption Properties by Forming Mg−x wt % ZrCrCu Composites Shivani Agarwal,*,‡ Ankur Jain,*,†,‡ Pragya Jain, Mukesh Jangir, and I. P. Jain Centre for Non-Conventional Energy Resources, University of Rajasthan, Jaipur - 302004, India
ABSTRACT: Composite formation with Zr-based Laves phase alloys, especially the ZrCr2 family, is an effective method to improve the hydriding properties of MgH2. The present paper describes a systematic study of the reaction pathway of Mg−x wt % ZrCrCu composites (x = 25, 50) in terms of their structural, morphological, and hydrogenation properties. XRD and SEM results show no interaction between Mg and the ZrCrCu alloy phase during composite preparation by high-energy ball-milling. However, hydriding/annealing cycles lead to the formation of the Mg2Cu phase at grain boundaries of the Mg−ZrCrCu matrix. This Mg2Cu phase does not interact with the hydrogen at the studied condition, but provides several diffusion paths and stable nucleation sites for the formation of MgH2, and thus enhances the sorption kinetics. Pressure composition temperature (PCT) analysis shows a reduction in desorption temperature down to 250 °C for these composites.
1. INTRODUCTION Magnesium as a hydrogen storage material has attracted attention due to its high hydrogen content (7.6 wt %), low cost, and easy availability.1 Despite its merits, Mg could not be used onboard due to its high stability and slow kinetics. The hydrogenation/dehydrogenation reaction for pure Mg occurs only at 350 °C.2 Several approaches have been adopted so far to improve the sorption characteristics, including thermodynamics and kinetics. Ball-milling/mechanical milling is the most popularly adopted method, which creates a fresh surface and structural defects in the material.3,4 The formed defects and grain boundaries allow easy diffusion of hydrogen from the surface to the bulk material.5 However, this method has limitations to achieve the nanocrystallite size that is required (
