Ohmic drop effects in square-wave voltammetry

Abstract

The ohmic drop effects in square-wave voltammetry (SWV) are studied theoretically. Three different electrode mechanisms are considered: (i) simple redox reaction of a dissolved redox couple, (ii) redox reaction with adsorption of the reactant and (iii) surface redox reaction of a strongly immobilized redox couple. The ohmic drop effect is represented through the complex dimensionless resistance parameter defined as ρ=(nF)2S(cOx)0(Df)1/2RΩ(RT)−1 for (i) and (ii) and ρs=(nF)2SΓ0RΩf(RT)−1 for (iii). The relationships between the properties of the SWV response and the resistance parameters are investigated thoroughly. An attempt is made to establish criteria for distinguishing the kinetic from the ohmic drop phenomena. The influence of the ohmic drop on the quasi-reversible maximum in the case of adsorption-complicated redox reactions (ii) and (iii) is analyzed. The error that can be involved in the estimation of the standard rate constant using the quasi-reversible maximum in the presence of ohmic drop is evaluated in the case of the surface redox reaction (iii).