Scanning electrochemical microscopy. 45. Study of the kinetics of oxygen reduction on platinum with potential programming of the tip

Scanning electrochemical microscopy (SECM) was used to study the kinetics of oxygen reduction on platinum in alkaline media. Oxygen was generated at a gold tip by oxidation of OH- and reduced at a Pt substrate. The formation of anodic film on the surface of the gold tip caused instability in tip behavior. This problem was overcome by applying a potential program at the tip to obtain the stable steady state tip current that is important for quantitative SECM analysis. The Tafel slope (125 mV, corresponding to a transfer coefficient, alpha, of 0.47) and the rate constant for oxygen reduction obtained by fitting the approach curves (2 x 10(-3) cm s(-1) at the open circuit potential) agree with previous results obtained by the rotating ring disk electrode technique and other electrochemical methods.