A new strategy for remarkably improving anti-disproportionation performance and cycling stabilities of ZrCo-based hydrogen isotope storage alloys by Cu substitution and controlling cutoff desorption pressure

ZrCo1-xCux (x = 0-0.3) alloys for hydrogen isotope storage were prepared via induction levitation melting. The effects of partial substitution of Cu for Co on the microstructure, hydrogen storage properties including hydriding-dehydriding kinetics, thermodynamic characteristics, cycling stability and related mechanism have been systematically investigated. It is found that all synthesized alloy ingots consist of ZrCo main phase, the grain size is further refined but the segregation of Cu element at grain boundary is more serious with the increase of Cu content. The pressure-composition isotherms for dehydrogenation show that both ZrCoH3 and ZrCo0.9Cu0.1H3 hydrides undergo one-step desorption, while ZrCo0.8Cu0.2H3 and ZrCo0.7Cu0.3H3 hydrides experience two-step desorption since a new middle hydride phase of ZrCoH0.8 with CrB-type orthorhombic structure is discovered during their dehydrogenation. This result is proposed to be linked with the changed electronic structure and lattice distortion induced by Cu substitution. To compare their dehydriding kinetics, the apparent activation energies for hydrogen desorption of different hydride phases in the alloys are also calculated systematically, and the value of E-a for hydrogen desorption of ZrCoH3 phase is decreased from 118.02 kJ/mol to 95.90 kJ/mol, 77.98 kJ/mol and 78.65 kJ/mol, respectively. Prominent cycling stabilities of the Cu-substituted alloys are obtained and follow the trend: ZrCo0.8Cu0.2 > ZrCo0.7Cu0.3 > ZrCo0.9Cu0.1 > ZrCo. Specifically, the optimum cycling stable capacity of ZrCo-based alloy is increased from 0.4 wt % to 1.21 wt %. Furthermore, the ZrCo0.8Cu0.2 alloy exhibits further enhanced cycling stability during the cycle by controlling cutoff desorption pressure at 0.253 bar, where only the first-step dehydrogenation happens. Therefore, a new strategy for improving anti-disproportionation performance of ZrCo-based alloys by controlling cutoff desorption pressure is also proposed, which is in favor of the enhanced cycling stability and further application of Cu-substituted ZrCo-based alloys for hydrogen isotope storage and delivery in the International Thermonuclear Experimental Reactor (ITER). (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.