Resistance change of an evaporated platinum film working as cathode or anode in acid solutions—III. Mechanism of oxygen-electrode reaction elucidated from rates of adsorption and desorption of oxygen

Abstract

From measurements of resistance changes of an evaporated platinum film working as anode or cathode during galvanostatic polarization in 10 −3 N sulphuric acid solution, the following results were obtained. 1. (1) In the initial stage of anodic polarization (amount of anodic charge, q pr, <1–1·5 mC/cm 2), oxygen is stoichiometrically adsorbed as (OH). 2. (2) With increase of q pr above these values, molecular oxygen is generated through electrochemical desorption of atomic oxygen, with a rate proportional to the amount of atomic oxygen on the electrode and to the cd of anodic polarization. 3. (3) The electrochemical generation of molecular oxygen proceeds through two parallel paths, ie, through adsorbed species (the c 3 species) and without adsorption. 4. (4) The amount of the c 3 species accumulated decreases after the interruption of anodic current, controlled by the rate of diffusion at the initial stage, and controlled afterwards by the rate of desorption. The c 3 species is presumed to be physisorbed molecular oxygen. 5. (5) The current efficiencies of coulometry of spontaneously decreasing species are calculated and compared with observation; the results suggest that the rates of some decay reactions are diminished by the flow of the coulometric current. 6. (6) The processes and species characterizing each stage on the resistance/time or potential/time curves during galvanostatic polarization are interpreted in terms of chemical reactions and species.