Cathodic reduction of oxygen on copper and brass

Abstract

In this investigation, the electrochemical reduction of oxygen on copper and brass has been studied using the ring-disc electrode technique in solutions containing chloride, sulphate and nitrate anions and ammonium cation. The E—I curves obtained in the forward and reverse direction of polarization for copper and brass in NaCl, Na 2SO 4 and NH 4Cl solutions are similar in nature and show two waves. However in (NH 4) 2SO 4 and NH 4Cl solutions are similar in nature and show two waves. The rate of oxygen reduction is the highest in ammonium sulphate for both copper and brass whereas it is the lowest in NH 4Cl in the case of copper. In Na 2SO 4 and NaCl solutions, the rate of oxygen reduction is higher on copper than on brass. Apparent Tafel slopes for oxygen reduction obtained for copper and brass vary from 65 mV to 240 mV depending upon the medium. The two steps observed with copper disc electrode have been identified as due to the reduction of oxygen to hydrogen peroxide and reduction of H 2O 2 to OH − ion or water depending upon the pH of the solution. In acid chloride and sulphate media no H 2O 2 was detected, which suggests direct reduction to H 2O. The diagnostic plots of I d / I r υ s ω − 1 2 employed by Bockris et al indicate that in Na 2SO 4 the reduction of oxygen to H 2O 2 takes place in a parallel reaction whereas in (NH 4) 2SO 4 both direct reduction of O 2 to water (or OH − ion) and the reduction through intermediate H 2O 2 occur.