The effect of the addition of small quantities of gallium to high-purity aluminium (99.999 wt%) on its electrochemical behaviour at high cathodic potentials (up to -2.0 V versus SCE), has been investigated using the potentiostatic pulse method. After cathodic polarization, anodic current was traced versus time to determine the quantity of charge necessary for oxidation of substances formed. Anodic current responses to the return to the E (OCP) were also recorded in the period of 1 s. Time responses of the cathodic and anodic currents were analyzed. The cyclic voltammetry method was used to determine the hydration potential. The range of low and high cathodic potentials (LCP, HCP) was defined for all the samples. It has been established that the oxide film retains its properties in the LCP range, while in the HCP range cathodic breakdown and hydration of the oxide take place. Electrochemical methods complemented the SEM and EDAX analysis before and after the cathode pulse of -1.9 V versus SCE.