Abstract
Many industrial applications require hydrogen purification, and metal hydrides can serve this purpose. In this study, the effects of gaseous impurities like CO2, CH4, and O2 on the hydrogen cycling behavior of commercial Ti-Fe-Mn were carefully studied. Impurities of O2 and CO2 considerably lower the hydrogen storage capacity of the materials, whereas CH4 has a lesser effect. According to the results of the microstructural characterization, upon hydrogen cycling, a shell of oxides and carbonates forms at the Ti-Fe-Mn particles surface, acting as a barrier for the hydrogen diffusion but at the same time preventing the further interaction of the alloy core with the gaseous impurities. The first-principles calculations based on density functional theory reveal that Fe-Ti-Ti threefold, Ti-Ti bridge, Mn-Ti-Ti threefold, and Fe-Ti-Ti threefold are the favored sites for the adsorption of CO2, CH4, H and O, respectively. Remarkably, the samples can be regenerated at 90°C, a temperature so moderate that it is ideal for the practical use of the Ti-Fe-Mn hydrogen storage system.
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