Chronoammetry and Chronopotentiometry on Electrodes with a Microrough Surface: Theoretical Consideration

Abstract

The problem of transient two-dimensional diffusion to a microrough electrode under galvano- and potentiostatic polarization conditions is solved. The effect of the scale and morphology of roughness, as well as the diffusivity on the time dependences of I current and η overpotential is analyzed. Both of them are found to be practically independent of the type of the roughness, while its degree (the microroughness factor f _r ) decisively affects the shape of the current- and overpotential-decay curves. At a relatively short polarization when the diffusion front profile repeats the electrode surface relief, the parameters of transient electrochemical methods (the I current in the potentiostatic measurements and the τ^1/2 rooted transient time in the galvanostatic ones) linearly depend on the microroughness factor. Upon a relatively long polarization when the diffusion front is noticeably distant from the surface and almost planar, the current and overpotential values fit in with classical equations of chronoammetry and chronopotentiometry, being independent of f _r . At a thickness of the diffusion layer comparable to the height of surface irregularities, the current (as well as the rooted transient time) ratio of the microrough to perfectly smooth electrode surface looses its linear dependence on the surface parameters. The time location of this range is chiefly determined by the diffusivity and the mean distance between the microscopic surface irregularities.