LIMITING DIFFUSION CURRENTS UNDER CONDITIONS OF LOCAL HEATING OF ELECTRODE

For a reversible [Fe(CN)(6)](-3/-4) system, limiting anodic and cathod ic currents are measured at a platinum electrode under conditions of i ts heating with red light. With increasing temperature Delta T of the electrode relative to the bulk solution, the anodic current increases monotonically, and the cathodic current passes through a minimum. This may be explained by an increase in the solution density in the vicini ty of the electrode for the cathodic current and by its decrease for t he anodic current under the conditions of natural convection. Stable a uto-oscillations of the current are found near the cathodic current mi nimum. Thermal impedance of the system is calculated by the Fourier tr ansformation of nonsteady-state limiting currents. From the analysis o f frequency spectrum of thermal impedance, thickness and relaxation ti me of near-surface layer are estimated, and from the steady-state meas urements, a concentration dependence of solution density in the electr ode vicinity was determined.