REACTIVE DEPOSITION OF COBALT ELECTRODES - V MECHANISTIC STUDIES OF OXYGEN REDUCTION IN UNBUFFERED NEUTRAL SOLUTIONS SATURATED WITH OXYGEN

The mechanism and kinetics of oxygen reduction were studied with a rotating Pt ring-Ni disk electrode in unbuffered neutral solutions saturated with oxygen. It was found that oxygen reduction is a first-order reaction with respect to the oxygen concentration in unbuffered neutral solutions. The current ratio of the two-electron reaction is about 18.2% in KCl solution, as compared to 4.6% in K2SO4 solution and only 1.7% in CH3COOK. The presence of Cl- ions in the solution greatly promotes the two electron process, with the production of about 30.8% hydrogen peroxide. A mechanism involving a determining step of the first charge transfer under Langmuir adsorption conditions has been proposed for O2 reduction in chloride solutions. However, in CH3COOK, O2 is primarily reduced through a four-electron reaction, since little hydrogen peroxide has been detected. IN cobalt solutions, Co(OH)2 is formed at the electrode surface as the result of the preceding O2 reduction. It has been confirmed that the formation of the Co(OH)2 as well as its stability are directly related to the mechanism and kinetics of O2 reduction.