Abstract
Corrosion of pristine AB5-type metal alloy LaMm-Ni4.1Al0.3Mn0.4Co0.45 in the aqueous solutions of alkali metal hydroxides of diverse composition and concentration was tested. Correlation was observed between the alloy corrosion intensity in various hydroxide solutions, and its electrochemical capacity in these electrolytes. Mm(OH)3, CoO(OH), and nickel metal aggregates were detected among the products of selective oxidation of the alloy. High intensity corrosion of the alloy was observed in RbOH and CsOH solutions leading to formation of ternary oxides at the surface of the alloy. Presence of rubidium and cesium ions in the electrolyte were found to create an additional driving force for lanthanides (La and Ce) to leave the lattice of the alloy, thus, enhancing its corrosion. Corrosion, together with mechanical degradation, were found to be the main reasons of deactivation of LaMm-Ni4.1Al0.3Mn0.4Co0.45 alloy upon elongated electrochemical treatment.
Highlights
Nickel-metal hydride batteries (Ni-MH) are still one of the most popular electrochemical power sources
Mechanical degradation of the active material, LaNi5 -type hydrogen storage alloy, occurs due to the tension appearing in the lattice between charged and discharged regions, which have different molar volumes due to the insertion of hydrogen into the alloy, where the molar volume of hydrogenated LaNi5 alloy is up to 24% larger than the molar volume of dehydrogenated material [7]
In this paper we present a study on corrosion and degradation of an AB5 -type alloy occurring in contact with various alkali metal hydroxide solutions
Summary
Nickel-metal hydride batteries (Ni-MH) are still one of the most popular electrochemical power sources. The Ni-MH batteries, due to their high reliability and safety level, serve as a stationary uninterruptible power supply for various applications [5]. Nowadays, they are usually used to power high current demanding mobile devices, like digital cameras, flashlights, or electric vehicles, filling the gap between the heavy lead-acid batteries (starting batteries for combustion engines) and the light lithium-ion batteries (present in mobile electronic devices). One of the most challenging features of the Ni-MH batteries is the loss of their overall capacity in a function of charging-discharging cycles being observed due to degradation and deactivation of anodic material over time [6]. Mechanical degradation of the active material, LaNi5 -type hydrogen storage alloy, occurs due to the tension appearing in the lattice between charged and discharged regions, which have different molar volumes due to the insertion of hydrogen into the alloy, where the molar volume of hydrogenated LaNi5 alloy is up to 24% larger than the molar volume of dehydrogenated material [7]
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