Key Takeaways & Executive Findings
- •• • In pure hydrogen, the alloy retains 72.64% capacity after 10 cycles, recovering to 98.27% after 473 K dehydrogenation; after 22 cycles, capacity loss is recoverable, demonstrating inherent cyclability. • • After 10 poisoning cycles, H2S and CO reduce capacity retention to 3.56% and 2.71%, respectively; after 20 cycles, values are 3.68% and 1.73%, indicating severe poisoning with CO being more potent. • • Regeneration at 473 K restores capacity to 40.35% for H2S-poisoned alloy versus 98.27% for CO-poisoned alloy, proving H2S poisoning is largely irreversible while CO is reversible. • • XPS analysis confirms H2S forms CaS and CaSO4 on the surface (irreversible chemical adsorption), whereas CO adsorbs reversibly without new compounds, guiding alloy design to reduce Ca content for enhanced H2S tolerance.
Abstract
The high cost of high-purity hydrogen necessitates the utilization of low-cost industrial by-product hydrogen as an alternative gas source to reduce hydrogen storage costs. Industrial by-product hydrogen typically contains impurities such as H2S and CO, yet the poisoning mechanisms of these gases on superlattice hydrogen storage alloys during hydrogen absorption/desorption remain poorly understood. This study systematically investigates the poisoning effects and regeneration behavior of La0.65Mg1.32Ca1.03Ni9Y0.17 superlattice hydrogen storage alloy in atmospheres containing 10^-3 H2S and CO. The experimental protocol comprised 10 poisoning cycles followed by 1 regeneration, repeated to total 20 poisoning cycles and 2 pure hydrogen regenerations. Results show that in pure hydrogen, the alloy's hydrogen storage capacity gradually decreases after 22 cycles but is effectively restored after dehydrogenation at 473 K. In the presence of impurity gases, the hydrogen storage capacity retention rates after 10 poisoning cycles with H2S and CO are 3.56% and 2.71%, respectively; after 20 cycles, these decrease to 3.68% and 1.73%, respectively. After dehydrogenation at 473 K, retention rates recover to 40.35% and 98.27%, respectively. This indicates that poisoning severity follows the order CO > H2S, while regeneration difficulty follows H2S > CO. X-ray diffraction analysis reveals that after poisoning, the main phase transforms from AB3 to AB3H, but reverts to AB3 after high-temperature dehydrogenation. X-ray photoelectron spectroscopy shows that after H2S poisoning, CaS and CaSO4 form on the alloy surface, indicating irreversible chemical adsorption. In contrast, after CO poisoning, no new substances are detected, indicating reversible adsorption. This study clarifies the differentiated poisoning mechanisms of impurity gases and provides theoretical support for the application of rare-earth superlattice hydrogen storage alloys in complex atmospheres.
1. Introduction
The commercialization of hydrogen energy is hindered by the high cost of high-purity hydrogen, which is typically produced via energy-intensive processes. Industrial by-product hydrogen, such as that from chlor-alkali or petrochemical industries, offers a low-cost alternative but contains trace impurities like H2S and CO that can poison hydrogen storage alloys. Rare-earth superlattice hydrogen storage alloys, such as La-Mg-Ni-based systems, are promising for solid-state hydrogen storage due to their high capacity and moderate operating conditions. However, their susceptibility to impurity poisoning has limited their deployment in real-world applications where gas purity is not guaranteed.
Previous studies have focused on the poisoning effects of individual impurities on conventional AB5 or AB2 alloys, but systematic investigations on superlattice alloys and the underlying mechanisms are scarce. This study addresses this gap by evaluating the anti-poisoning performance of a novel La0.65Mg1.32Ca1.03Ni9Y0.17 alloy under controlled H2S and CO exposures, employing a cyclic poisoning-regeneration protocol. By correlating capacity retention with structural and surface chemical analyses, the work delineates the distinct poisoning mechanisms—irreversible sulfide formation for H2S versus reversible adsorption for CO—and proposes compositional adjustments to mitigate poisoning. These findings provide critical insights for designing robust hydrogen storage materials for industrial hydrogen streams.
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Tianmeng HE, Yajie ZHANG, Xiaoyi XUE, He ZHANG, Shubin ZHANG, Jinpeng WANG, Hao WANG, Yanrong LIU (2026). Study on Anti-poisoning Property and Mechanism of Rare Earth Superlattice Hydrogen Storage Alloys. The Chinese Journal of Process Engineering. https://doi.org/10.12034/j.issn.1009-606X.225264
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Frequently Asked Questions
What is the quantitative impact of H2S and CO impurities on the hydrogen storage capacity of the La0.65Mg1.32Ca1.03Ni9Y0.17 alloy after 20 poisoning cycles?
After 20 poisoning cycles, the capacity retention rates are 3.68% for H2S and 1.73% for CO, indicating that CO causes more severe capacity loss than H2S under identical conditions.
How effective is high-temperature dehydrogenation at 473 K in regenerating the alloy after poisoning by H2S and CO?
After 473 K dehydrogenation, the capacity retention recovers to 40.35% for H2S-poisoned alloy and 98.27% for CO-poisoned alloy, demonstrating that CO poisoning is largely reversible while H2S poisoning is not.
What are the underlying mechanisms for the different poisoning behaviors of H2S and CO on the alloy surface?
XPS analysis reveals that H2S reacts with Ca to form CaS and CaSO4, which are irreversible chemical compounds, whereas CO does not form new surface species, indicating reversible physical/chemical adsorption.
How does the alloy's crystal structure change upon poisoning and after regeneration?
XRD shows that the initial AB3 phase transforms to AB3H after poisoning, but reverts to the AB3 main phase after high-temperature dehydrogenation, indicating structural reversibility.
What design strategy is suggested to improve the alloy's resistance to H2S poisoning?
Given that H2S preferentially reacts with Ca, reducing the Ca content in the alloy while preserving the AB5/A2B4 superlattice structure could mitigate irreversible sulfide formation and maintain high hydrogen storage capacity.
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