Diffusion conductivity of electrode processes under conditions of natural convection

The diffusion conduction sigma = di/deta (where i is the current and eta is the overvoltage) in reversible system [Fe(CN)(6)](3-/4-) is measured by the electrochemical impedance method under isothermal and nonisothermal conditions of natural convection. Platinum disk electrodes 3 min and 20 mum in diameter are used. For a macroelectrode under isothermal conditions, c; passes through a maximum near equilibrium and tends to zero at eta --> 0. Under nonisothermal conditions and for a microelectrode under isothermal conditions, sigma achieves a maximum near equilibrium. These data correlate with the eta dependence of the diffusion layer thickness and quantitatively agree with theory.