Dependence of constituent elements of AB5 type metal hydrides on hydrogenation degradation by CO2 poisoning

Abstract LaNi 5 -based AB 5 type alloy has high tolerance to CO 2 poisoning for hydrogen purification and storage from 20 to 25% CO 2 mixed gas. To elucidate the CO 2 poisoning factors of AB 5 type alloys, which are LaNi 5 , CaNi 5 , LaCo 5 , and MmNi 4.025 Co 0.4 Mn 0.275 Al 0.3 (Mm-Ni), the dependence of the constituent elements has been investigated on hydrogenation degradation by CO 2 poisoning. The tendency of CO 2 poisoning magnitude is CaNi 5 5 5 , which was evaluated by the hydrogenation rate and capacity under CO 2 partial pressure and after CO 2 exposure. The Ni element of B site in CaNi 5 and LaNi 5 is an important role to maintain higher tolerance of CO 2 poisoning compared to Co element in LaCo 5 . Moreover, the element of A site effects on CO 2 poisoning magnitude in AB 5 type alloy. The experimental tendency of CO 2 poisoning magnitude is consistent with the theoretical CO 2 adsorption energy on the ( 10 1 ¯ 0 ) surface plane of −1.39, −2.05, and −2.68 eV for CaNi 5 , LaNi 5 , and LaCo 5 , respectively. CO 2 adsorbs on B site with electron charge transfer from AB 5 alloys to carbon. Not only Ni element in B site but also Ca element in A site decreases the energy of CO 2 adsorption on B site in AB 5 type alloys.