Square-wave voltammetric evaluation of electrochemical constants: Comparative study with other techniques

Abstract

Square-wave voltammetry was employed for evaluation of electrochemical rate constants for soluble hexacyanoferrate ions as well as for iron hexacyanoferrate (Prussian blue) and nickel hexacyanoferrate immobilized on carbon electrodes. Modelling of square-wave response of immobilized species with assumption of Nernstian behavior, the dimensionless net current peak splitting occurs. The peak value decreases with the rise of square-wave amplitude Esw and splits around the common value of 50 mV. For a quasireversible behavior, the dimensionless net peak current has an extremum depending on both frequency and Esw. At 40 mV, the frequency in the extremum almost coincides with the surface electrochemical rate constant ksur. For practical confirmation, the Prussian blue film was studied at different frequencies (Esw = 50 mV). At lower values, the reaction is relatively fast and net peak current splitting occurs. At higher values, the net response reaches its maximum allowing to evaluate the surface electrochemical rate constant. A comparative investigations of electrode kinetics (for both surface and heterogeneous electrochemical constant) by different electrochemical methods proved the advantages of square-wave pulse technique. In contrast to cyclic voltammetry and electrochemical impedance spectroscopy, the square-wave voltammetry has lower variation of estimated parameters, relatively simple calculations, uncomplicated simulation of different mechanisms.