Significant improvement of electrochemical hydrogenation, corrosion protection and thermal stability of LaNi4·6Zn0.4-xLix (x ≤ 0.2) solid solution phases due to Li-doping

Abstract

The electrochemical hydrogenation, structure and thermal stability of LaNi4·6Zn0.4-xLix (x ≤ 0.2) intermetallic compounds have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) with WDS/EDX, differential scanning calorimetry (DSC) and electrochemical techniques: potentiodynamic polarization, charge/discharge, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS). The synthesized LaNi4·6Zn0.4-xLix intermetallics are solid solutions on the basis LaNi5 compound with hexagonal CaCu5 structure type. Precise structural studies by single crystal methods revealed that with the increase of lithium content in the phase, the hexagonal unit cell is transformed into a new orthorhombic structure (Cmmm, a = 5.0068 (10), b = 8.6719 (17) Å, c = 3.9952 (8) Å). The LaNi4·6Zn0.4-xLix intermetallics effectively passivate in 6 M KOH over a wide potential range. The presence of lithium in the solid solution phase improves corrosion resistance of LaNi4·6Zn0.4-xLix intermetallics compared to the reference compound (LaNi5). The electrochemical measurements show that LaNi4·6Zn0.4-xLix intermetallic compounds absorb hydrogen, and the highest effectiveness of hydrogen absorption shows LaNi4·6Zn0·2Li0.2 compound with orthorhombic structure. The DSC/TG results indicate greater thermal stability of compounds doped by Zn (LaNi4·6Zn0.4) and Zn/Li (LaNi4·6Zn0·2Li0.2) in compare to LaNi5.