On some dynamic peculiarities of the charge transfer with adsorption and attractive interactions

Abstract

Complex electrode reactions with adsorption of intermediate product and with attractive interactions accounted for by Frumkin adsorption isotherm may show up a variety of unusual steady states (ss) characterized by ss adsorption isotherms. Under symmetry of kinetic equations the single peculiarity to be expected in electrochemical adsorption and desorption reactions is hysteresis responsible for current discontinuities in potential sweep experiments and similar discontinuity of immittance data recorded for potential or frequency sweeps. For asymmetry of partial reactions, as for charge transfer coefficients different then 0.5 or unequal charge numbers in partial reactions, the steady-state isotherms get unusual forms described in the chemical dynamics literature as “mushrooms” or “isolas”, this last term referring to disjoined branches of the ss isotherm. In potential scan experiments, these isotherms present double hystereses and irreversible switches between steady states’ branches at high and at low surface coverage.