Modification of activation and corrosion properties of LaNi4.5Co0.5 HSA by ball milling with Zn and preferential alkaline leaching

Abstract

LaNi4.5Co0.5 hydrogen storage alloy (HSA) was modified by 9.4 and 17.1 mass percent Zn additions and ball milling (BM). The amorphous powder was then subjected to alkaline leaching for selective dissolution of amphoteric Zn and thus surface activation. Long-lasting leaching (720 h) of powder in hot 0.5 M KOH solution allowed removal of 75–77% of Zn from the amorphous material. The modified materials revealed evidently faster (over 3 times) activation for hydrogen sorption both from the gaseous (H2) phase and in conditions of electrochemical cycling. Exchange current densities of H2O/H2 system stabilize after 30–40 cycles for untreated and leached materials on similar levels: 70 and 80 mA/g, respectively. Additionally, Zn-rich residues remaining within the powder particles after leaching play the role of an anodic protector which efficiently inhibits electrochemical corrosion degradation of the negative electrode material. As a result, the modified electrode materials do not display any capacity fade during 60 cycles at −0.5C/+0.5C charge/discharge rates.