Key Takeaways & Executive Findings
- •• CH4 poisons TiFe0.9 alloy via physical coverage without chemical reaction, while CO and CO2 block active sites for H2 dissociation and absorption. • O2 reacts with the alloy surface to form a passivating layer that prevents hydrogen uptake, highlighting the need for surface protection. • DFT calculations reveal adsorption energy relationships that explain the experimental poisoning mechanisms, providing a predictive tool for alloy design. • The findings guide the development of Ti-based high-entropy alloys with enhanced resistance to impurity gas poisoning for practical hydrogen storage.
Abstract
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 TiFe0.9 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.
1. Introduction
As a clean, efficient, and sustainable energy carrier, hydrogen could replace fossil fuels in the future. However, safe and efficient hydrogen storage technology is crucial [1–6]. TiFe alloys, typical representatives AB-type hydrogen-storage alloys [7–11], have received extensive attention owing to their low cost and outstanding characteristics, including their theoretical hydrogen storage capacity (1.86wt%), reversible hydrogen absorption and desorption process. TiFe alloys meet the requirements of industrial applications, giving them certain advantages in industrial production [12–16].
However, TiFe alloys usually require more than ten cycles of high-temperature activation to carry out normal hydrogen absorption/dehydrogenation processes. The requirement for high-temperature activation has hindered the practical application of TiFe alloys in hydrogen storage. Fortunately, Dematteis et al. [17] showed that activation at room temperature can be achieved by changing the composition of TiFe alloys. The TiFe0.9 alloy can be activated at room temperature and moderate hydrogen pressure compared to the poor activation kinetics of equimolar TiFe alloy. Therefore, we selected the TiFe0.9 alloy for the study on the premise of not changing the alloying elements based on previous literature.
However, the TiFe alloy still faces some urgent problems in practical applications, among which the poisoning problem caused by impurity gases is particularly prominent [18–19]. In actual hydrogen production and application processes, hydrogen often inevitably contains a small amount of impurity gases, such as CO, CO2, O2, and H2S [20]. Even trace amounts of impurity gases can significantly degrade the hydrogen-storage performance of TiFe alloy by reacting with its surface to form various compounds (oxides, hydroxides, and carbonyls) [21–22]. This not only reduces the hydrogen adsorption capacity of the material but also adversely affects the hydrogen adsorption/desorption kinetics, ultimately shortening the cycle life of the material [23–27]. In addition, these impurities have the potential to deactivate the surface centers responsible for H2 dissociation, thereby delaying a process that constitutes a rate-limiting step in hydrogen absorption [28–30].
Therefore, in-depth research on the poisoning mechanism of impurity gases on TiFe alloys is of great significance. From a theoretical perspective, by revealing the poisoning mechanism, we can gain a deeper understanding of the nature of the interaction between the TiFe alloy and impurity gases, providing a theoretical basis for further optimizing the structure and performance of the alloy. Extensive efforts have been devoted to investigating the poisoning effects of ZrCo [22], Mg-based alloys [31], and LaNi5 [32], whereas studies on the poisoning resistance of Ti-based hydrogen storage alloys remain relatively scarce. The AB-type TiFe alloy is cost-effective but requires stringent activation conditions and exhibits sensitivity to impurities. Notably, TiFe alloys exposed to air are readily deactivated at room temperature owing to the lack of a protective surface barrier that can hinder detrimental oxidation processes [26,33]. However, most prior studies on TiFe hydrogen storage alloys involved pre-exposure solely to air, followed by
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Hangyan Shi, Yingxian Zhang, Zhenglong Li, Fan Gao, Xinqiang Wang, Yaxiong Yang, Yanxia Liu, Xuezhang Xiao, Fang Fang, Wen-Gang Cui (2025). Unraveling the poisoning mechanism of impurity gases on TiFe hydrogen storage alloys. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-025-3138-2
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Frequently Asked Questions
What are the main impurity gases that poison TiFe hydrogen storage alloys?
The main impurity gases are O2, CO, CO2, and CH4, which are commonly present in hydrogen streams and can significantly degrade the hydrogen storage performance of TiFe alloys.
How does CH4 poison TiFe alloys?
CH4 does not react chemically with the alloy but acts through physical coverage, blocking the surface and reducing hydrogen absorption capacity.
What is the poisoning mechanism of CO and CO2 on TiFe alloys?
CO and CO2 occupy the active sites for H2 dissociation and absorption, thereby impeding the hydrogen uptake process.
How does O2 affect TiFe alloys?
O2 reacts directly with the alloy surface to form a passivating oxide layer that prevents hydrogen absorption, leading to deactivation.
What is the significance of this study for hydrogen storage technology?
Understanding the poisoning mechanisms is crucial for designing Ti-based high-entropy alloys with enhanced resistance to impurity gases, thereby improving the practical applicability of TiFe alloys in hydrogen storage.
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