Abstract
The (de)hydrogenation properties of a TiFe intermetallic compound (IMC) alloy activated by cold rolling inside a glovebox at ambient temperature were investigated by kinetic measurements, x-ray powder diffraction (XRD), and transmission electron microscopy (TEM). Rate-limiting steps were identified by testing kinetic models on hydrogen absorption and desorption curves. To prevent surface poisoning during air exposure, the TiFe IMC was also cold rolled with polytetrafluoroethylene (PTFE) and ultra-high molecular weight polyethylene (UHMWPE). The addition of either PTFE or UHMWPE to nanostructured TiFe by cold rolling did not produce a polymer-metal composite with O2 poisoning resistance, regardless of the polymer-mixing way adopted. This occurred because large surfaces of the particles were not adequately coated with polymer. The results identify challenges to the TiFe IMC polymer-covered material that must be overcome before a methodology can significantly contribute to the formation of nanostructured TiFe-polymer composites with enhanced hydrogen storage properties. The diffusion-controlled reactions in the cold-rolled TiFe IMC without polymer were prevalent in all cases, as predicted by the Jander three-dimensional diffusion model. The main contribution of this work regards estimation of the amount of hydrogen released, which was 0.60% after 6 min and reproducible for the three subsequent cycles.
Highlights
The TiFe intermetallic compound (IMC) is a low-cost material of great interest to hydrogen storage in the solid-state due to its theoretical hydrogen storage capacity (1.9 wt.%) at ambient temperature
Scanning electron microscopy (SEM) analysis was carried out in the Philip XL-30 FEG microscope equipped with energy dispersive x-ray spectrometry (EDS) to evaluate the particle size, microstructure defects, and surface features of the particles and to understand the effectiveness of the polymer covering applied through the cold rolling route
The cold rolling process causes the x-ray powder diffraction (XRD) peaks to reduce in intensity with the disappearance of the two small peaks around 30 and 71°, which agrees with the larger amount of powder particles produced through
Summary
The TiFe intermetallic compound (IMC) is a low-cost material of great interest to hydrogen storage in the solid-state due to its theoretical hydrogen storage capacity (1.9 wt.%) at ambient temperature. The addition of specific polymers to hydride-forming metal powders has been the subject of some experimental studies that aimed to produce nanostructured metal‐polymer composite materials with the potential of simultaneously react with hydrogen and resist surface poisoning. This ensures good mechanical stability, high thermal conductivity, fast kinetics, reproducibility, and durability to these composites[36,37,38,39,40,41,42]. Recognizing the role of surface in the reactivity of metallic materials with hydrogen and the impurities present in the air, this investigation includes an analysis of the use of the cold rolling process to produce nanostructured TiFe with polymer covering in an attempt to improve its resistance to air
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