Cathodic behavior of pure Al in sulfate media
Résumé
The cathodic behavior of Al in 0.5 M Na2SO4 solution was studied by electrochemical methods. It was shown that the reduction of Fe(CN)63- was difficult when an oxide layer was formed on the electrode surface during 1 h immersion in 0.5 M Na2SO4 solution due to the poor ionic and electronic conductivities of Al hydroxides. This reaction required a high cathodic overpotential on Al surface pre-treated at –2 V/SCE Al and was kinetically more difficult in comparison to platinum. Rotating disk electrode measurements showed that oxygen reduction reaction (ORR) was controlled by kinetics on both Al pre-treated at –2 V/SCE and oxidized Al cathodic dissolution was controlled by the supply of OH– ions through H2 evolution and by ORR on both oxidized Al electrode and the Al surface pre-treated at –2 V/SCE. Polarization curves obtained at different pH values showed that no dissolution behavior was observed at pH 5, whereas in neutral and alkaline solutions, OH– ions production induced chemical dissolution of the hydroxide layer. In O2 supersaturated solution, it was shown that ORR kinetics were slightly favored.