Hydrogen diffusivity, kinetics of H2O/H2 charge transfer and corrosion properties of LaNi5-powder, composite electrodes in 6 M KOH solution

Meticulous analysis of galvanostatic charge/discharge dependencies of the LaNi5-based, powder composite electrode, in terms of determination of characteristic kinetic parameters of hydrogen storage electrode materials working in concentrated alkaline solution has been carried out. A special attention has been paid to the precise determination of charge and discharge times. The cathodic curves reveal their stepwise nature which allows to receive information of hydride material corrosion phenomena and determine the real time of atomic hydrogen absorption. The graphical way of determining of reduction times, based on differential cathodic curves is proposed. The knowledge of hydrogen absorption and desorption times allows to determine hydrogen diffusivity within the tested material with acceptable accuracy. The effect of external pressure (0.5-4 bar) on hydrogen absorption ability of LaNi5-based material is also discussed. The exchange current density of H2O/H-2 system distinctly increases with external pressure, at the same time, kind of gas atmosphere (Ar or H-2) scarcely affects the exchange current on the LaNi5 electrode. The hydrogen capacity increases when the charge/discharge rate decreases. The reduction times of oxide phases formed during electrode discharge can be a measure of material corrosion rate. It is shown that the rate of LaNi5 corrosion process strongly increases with the electrode cycling.