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

LaNi5-based AB(5) 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 AB(5) type alloys, which are LaNi5, CaNi5, LaCo5, 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 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 AB(5) type alloy. The experimental tendency of CO2 poisoning magnitude is consistent with the theoretical CO2 adsorption energy on the (1010) 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 AB(5) 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 AB(5) type alloys. (C) 2015 Elsevier B.V. All rights reserved.