The theory of adsorption pseudocapacity behavior is developed for a sequence of electrochemical reactions involving an ion discharge step which produces an adsorbed radical, followed by an "ion–atom" recombination reaction with or without desorption of the product of this step. The adsorption pseudocapacity behavior is deduced analytically particularly for the steady-state case and distinguished from the results obtained for assumed quasi-equilibrium in the ion discharge step when the succeeding step is rate-controlling. The effect of variation of the relative values of the rate constants of the discharge and of succeeding steps is investigated. It is shown that the capacity-potential behavior is sensitively dependent on the ratio of these rate constants, particularly for the case of adsorption isotherms involving a large value for the "heterogeneity parameter", r, defining the variation of energy of adsorption of the intermediates with coverage. Under the latter conditions, limiting coverages of the electrode by the adsorbed species are reached with increasing potential, depending on the relative values of the rate constants and the value of r.
Photocatalytic oxidation of ethanol using ultrasonic modified TiO2; an in-situ diffuse reflectance infrared spectroscopy study