Electrode reaction at Pt, O2(g)/stabilized zirconia interfaces. Part II: Electrochemical measurements and analysis

Abstract In order to make clear the reaction kinetics at the Pt, O 2 (g)/stabilized zirconia electrodes, measurements were made on the dc electrode conductivity, σ E , between 370 and 800°C and anodic and cathodic polarization at 700°C in the P O 2 range of 10 −4 −1 atm. Above 600°C, the log σ E versus log P O 2 plot showed maximum. Below 500°C, σ E was essentially constant irrespective of P O 2 . At 700°C, when the P O 2 was high, the limiting current appeared for anodic polarization. In the lower P O 2 , the limiting current was observed at the cathodic polarization. The results were analyzed based on the reaction model proposed in Part I of the present paper. Above 600°C, the diffusion of adsorbed oxygen atoms on the Pt surface was confirmed to be the rate determining step. The activation energy of the surface diffusion of O ad atoms on Pt was found to be 41 ± 2.5 Kcal/mol, and the heat of adsorption of O ad on Pt was 53 ± 4 Kcal/mol. Below 500°C, the reaction rate was determined by the dissociative adsorption of oxygen molecules on the Pt surface near the Pt/zirconia boundary. The activation energy of this reaction was about 37 ± 4 Kcal/mol.