LaNi5-based AB5 type alloy has high tolerance to CO2 poisoning for hydrogen purification and storage from 20 to 25% CO2 mixed gas. To elucidate the CO2 poisoning factors of AB5 type alloys, which are LaNi5, CaNi5, LaCo5, and MmNi4.025Co0.4Mn0.275Al0.3 (Mm-Ni), the dependence of the constituent elements has been investigated on hydrogenation degradation by CO2 poisoning. The tendency of CO2 poisoning magnitude is CaNi5 < LaNi5 << Mm-Ni < LaCo5, which was evaluated by the hydrogenation rate and capacity under CO2 partial pressure and after CO2 exposure. The Ni element of B site in CaNi5 and LaNi5 is an important role to maintain higher tolerance of CO2 poisoning compared to Co element in LaCo5. Moreover, the element of A site effects on CO2 poisoning magnitude in AB5 type alloy. The experimental tendency of CO2 poisoning magnitude is consistent with the theoretical CO2 adsorption energy on the (101¯0) surface plane of -1.39, -2.05, and -2.68 eV for CaNi5, LaNi5, and LaCo5, respectively. CO2 adsorbs on B site with electron charge transfer from AB5 alloys to carbon. Not only Ni element in B site but also Ca element in A site decreases the energy of CO2 adsorption on B site in AB5 type alloys.
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