CO-Resistant Al-Doped AB₅-Type Hydrogen Storage Alloys

The safe and stable hydrogen storage is a key challenge in the development of hydrogen energy. AB₅-type solid hydrogen storage is considered as a promising method due to its excellent reversible absorption/desorption performance and cycling stability at room temperature. However, AB₅-type hydrogen storage alloys are susceptible to poisoning by highly toxic industrial gases, such as CO. In practical applications, impurity poisoning significantly reduces hydrogen absorption/desorption ability. Previously, it was believed that doping Al element could significantly reduce the strength of CO absorption to achieve CO-resistant performance. Actually, the first-principles calculations in this study reveal that Al doping does not significantly reduce CO absorption strength (−2.28 eV compared to −2.08 eV for LaNi₅). Instead, Al-doped LaNi₅ acts as a catalyst to promote the methanation reaction of CO at a high temperature of 125°C. The conversion pathway is CO → HCO → CH → CH₂ → CH₃ → CH₄, converting the highly toxic CO into the weakly toxic CH₄ and H₂O, with a capacity retention rate of 92% after 10 cycles. Furthermore, Al doping contributes to lowering the absorption plateau, thereby enhancing the alloy's competitiveness between H₂ and CO absorption (0.40 MPa compared to 1.63 MPa for LaNi₅). Thus, the exceptional CO tolerance of Al-doped AB₅ alloys is underpinned by the synergistic effect of CO methanation at elevated temperatures and reduced hydrogen platform pressure, providing a key mechanism for designing next-generation hydrogen storage materials that are resistant to industrial impurities.