A Comprehensive Voltammetric Characterisation of ECE Processes

Abstract

Using a diffusive-kinetic steady state theoretical treatment, a very simple analytical solution is deduced for the response of ECE-type processes at (hemi)spherical microelectrodes in normal pulse (NPV), derivative (DV) and steady-state voltammetries as well as in chronoamperometry. The more complex rigorous and kinetic steady state solutions for macroelectrodes (linear diffusion) are also presented for comparison.The above analytical expressions enable the very easy investigation of the influence of the chemical reaction and the difference between the formal potentials. The appearance of one or two separate signals as well as the value of the apparent number of electrons transferred are not only dependent on the relative formal potentials of the two redox couples but also on the kinetics and thermodynamics of the chemical reaction, the electrode size and the duration of the potential steps. These influences are thoroughly studied in NPV and DV and compared with the response in cyclic voltammetry (CV) under transient and stationary conditions. Procedures for the identification of the reaction mechanism and the characterization of the homogeneous chemical reaction are also discussed. The conditions where the impact of cross redox reactions (disproportionation-comproportionation) on the voltammetric response is relevant are established considering any chemical kinetics and electrode size.