Unraveling the poisoning mechanism of impurity gases on TiFe hydrogen storage alloys

TiFe alloys are AB-based hydrogen storage materials with unique characteristics and a wide range of applications. However, the presence of impurity gases (such as O₂, CO, CO₂, and CH₄) has a considerable impact on the hydrogen storage capacity and kinetics of TiFe alloys, drastically limiting their practical application in hydrogen storage. Consequently, in this study, we investigated the hydrogen absorption kinetics and cycling performance of the TiFe_0.9 alloy in the presence of common impurity gases (including CH₄, CO, CO₂, and O₂) and determined the corresponding poisoning mechanisms. Specifically, we found that CH₄ did not react with the alloy but acted through physical coverage. In contrast, CO and CO₂ occupy the active sites for H₂, significantly impeding the dissociation and absorption of H₂. In addition, O₂ reacts directly with the alloy to form a passivating layer that prevents hydrogen absorption. These findings were further corroborated by in situ Fourier transform infrared spectrometry (FTIR) and density functional theory (DFT). The relationship between the adsorption energies of the impurity gases and hydrogen obtained through DFT calculations complements the experimental results. Understanding these poisoning behaviors is crucial for designing Ti-based high-entropy hydrogen storage alloy alloys with enhanced resistance to poisoning.