Oxygen reduction on Cu–Zn alloys

Abstract

The reduction of oxygen on brass type Cu77Zn21Al2 in contact with 0.1 mol L-1 borax at pH 9.2 with and without chlorides was investigated and compared with the results on spectroscopic Cu. The surface film was characterized in situ by means of reflectance spectroscopy and by electrochemical impedance in the potential range negative to the open circuit potential. The main parameters associated to the kinetics of the oxygen reduction reaction were analyzed with a rotating disc electrode. The results show that within the potentials studied, a porous film was formed on brass while no significant spectral features were observed, except at -1.2 V where zinc oxo-hydroxides grow in chloride-free solutions and dissolve when chlorides are present in the system. The number of electrons exchanged for brass was close to 4 in both solutions, showing that oxygen is predominantly reduced to hydroxyl ions, with a reaction order equal to one. The residual presence of oxides on the surface results in Koutecky-Levich plots with slopes dependent on the applied potential and interfere with the calculation of the Tafel slope.