Microstructure and Hydrogen Storage Performance of Ball-Milled MgH2 Catalyzed by FeTi

Abstract

A high-energy ball-milling method was applied for different milling times (1 h, 3 h, and 10 h) to synthetize nanocrystalline MgH2 powder samples catalyzed by Fe2Ti. Morphology and microstructure of the powders were characterized by scanning electron microscopy and X-ray diffraction. The recorded diffraction profiles were evaluated by the convolutional multiple whole profile fitting algorithm, in order to determine microstructural parameters of the composites, such as average crystallite size and average dislocation density. Differential scanning calorimetry was performed to investigate the dehydrogenation characteristics of the alloys. It was obtained that there exists an optimal milling time (3 h) when desorption occurs at the lowest temperature. X-ray diffraction of partially dehydrided states confirmed a two-step H-release, including the subsequent desorption of γ-MgH2 and α-MgH2. The effect of milling time on the H-sorption performance was investigated in a Sievert-type apparatus. The best overall hydrogenation performance was obtained for the composite milled for 3 h.

Time-Dependent Multi-Particle Model Describing the Hydrogen Absorption of Nanocrystalline Magnesium Powders: A Case Study

“…The hydrogen kinetic measurement of the nanocrystalline MgH 2 powder was carried out in a home-made Sieverts' type equipment [64]. Isothermal dehydrogenation (10 kPa) and hydrogenation (1 MPa) experiments were obtained at 573 K. Partially absorbed states were achieved during the second hydrogenation cycle, when the absorption was interrupted at different hydrogen content, i.e., when 15%, 50%, and 90% of the Mg→MgH 2 reaction was completed.…”

“…where m is the Avrami-exponent and refers to the dimensionality of the growth process and c is a temperature dependent constant determining the rate of the process. JMA kinetics are usually valid for the desorption of catalyzed MgH 2 processed for prolonged HEBM time [54,62,64].…”

Synergetic Effect of FeTi in Enhancing the Hydrogen-Storage Kinetics of Nanocrystalline MgH2

“…As a continuation of the work described in [52], an increased amount of activated Fe-Ti powder (40 wt.%, 50 wt.% and 60 wt.%) was ball-milled with MgH 2 in the present study in order to induce a synergetic effect between the catalyst and the hydride on their overall hydrogenation kinetics. The work also demonstrates in detail the effect of the catalyst amount on the microstructure, morphology and hydrogenation/dehydrogenation performance of MgH 2 .…”

“…The hydrogen absorption capacity of the activated powders decreased with increasing FeTi content [51]. When activated Fe 2 Ti intermetallic powder was mixed with MgH 2 and subjected to HEBM, it was found that at the lowest temperature, coupled with a 6.9 wt.% H-storage capacity, there exists an optimal milling time (3 h) for desorption to occur [52]. Reasonable room temperature kinetics could be achieved in the Mg-TiFe 0.92 Mn 0.08 system if the transition metal additives reached at least 50 wt.%.…”

“…Fe-Ti compounds or solid solutions have gained noticeable attention as nanocrystalline Mg-FeTi composites are reported to have an outstanding hydrogenation performance [48][49][50][51][52][53][54][55]. For example, the kinetics of the MgH 2 -35 wt.% FeTi 1.2 composite at elevated temperatures is appropriately fast, and their longer ball-milling time promotes an increase in the H-sorption rate [49].…”