Effect of CO2 on hydrogen absorption in Ti-Zr-Mn-Cr based AB2 type alloys

The effect of CO2 on hydrogen absorption has been investigated for AB2 type alloys of Ti0.515Zr0.485Mn1.2Cr0.8 (Ti-Zr-Mn-Cr) and Ti0.515Zr0.485Mn1.2Cr0.8M0.1 (Ti-Zr-Mn-Cr-M, M = Fe, Co, or Ni) in order to develop metal hydrides for a hydrogen purification and storage system. A magnitude of CO2 poisoning tolerance was evaluated by comparing hydrogen absorption properties before and after CO2 exposure. As the results, an order of CO2 tolerance was Ti-Zr-Mn-Cr-Ni < Ti-Zr-Mn-Cr < Ti-Zr-Mn-CrCo < Ti-Zr-Mn-Cr-Fe. It suggests that the AB(2) alloys have dependence of additive 3d-transition elements on CO2 tolerance. Ti-Zr-Mn-Cr-Fe has the highest CO2 tolerance among them. The additive of Fe and Co improves tolerance of CO2 poisoning for hydrogen absorption properties. On the other hand, Ni element in AB(2) alloy decreases CO2 tolerance. The estimated enthalpy change between CO2 and the alloys surface was comparable to the formation of metal oxide. And the CO2-exposed AB(2) alloys after reacting with hydrogen desorbed methane gas. Therefore, CO2 would dissociate to CO and O on the surface of alloys, and then oxygen atom reacts with the alloys. (C) 2017 Elsevier B. V. All rights reserved.