A phenomenological model for macroscopic deactivation of surface processes

There is a wide class of electrochemical systems which present a sudden transition from a high to a low reaction rate region in function of an external parameter. This sudden transition is accompanied by the growth of a surface structure responsible for deactivation of the process. Analysing a simple phenomenological model of a generic surface process shows that the growth of this deactivating structure implies a hysteresis according a forward and reverse scan in the external control parameter. Application to water electrolysis, metal passivation and ethylene oxidation on Rh/TiO2/YSZ under open-circuit and under electrochemical promotion is discussed.