Analysis of Passivation and Corrosion Processes of Modified LaNi₅ Alloy-Based Hydride Electrodes

Studies were conducted on the effect of the partial substitution of nickel in an LaNi₅ alloy with germanium (5% by weight) or magnesium (3.3% by weight), in addition to surface modification using phosphomolybdic heteropolyacid (MPA) on the course of corrosion and passivation processes of hydrogen electrodes in a highly alkaline environment. The investigations were carried out by means of electrochemical impedance spectroscopy (EIS) and the potentiodynamic methods to analyse changes in the electrochemical parameters as a function of exposure time. The surface topography of the electrodes and chemical composition were investigated utilising a KEYENCE VHX-7000 digital microscope (Osaka, Japan) and a scanning electron microscope (SEM) equipped with an energy-dispersive spectroscopy EDS X-ray microanalysis attachment. The novelty of this work lies in the systematic, time-dependent comparison of the effects of bulk and surface modifications on the evolution of corrosion-passivation mechanisms of electrodes based on the LaNi₅ alloy. It has been shown that the Mg and Ge additives improve corrosion resistance in the initial stage of exposure but lead to destabilisation of the passive layer during prolonged electrolyte interaction. A different effect was observed for the MPA-modified electrodes, in which a stable protective layer forms, limiting corrosion while maintaining favourable hydrogen desorption kinetics. The obtained results indicate the key role of exposure time (>140 h) in shaping the corrosion mechanisms and emphasise the need for simultaneous optimisation of the alloy composition and surface properties in the design of durable hydrogen electrodes.