The Impact of Sinusoidal Amplitude on Visualising Thermodynamic Dispersion in Fourier Transformed AC Voltammetry

Abstract

Mathematical models of voltammetric experiments commonly contain a singular point value for the reversible potential, whereas experimental data for surface-confined redox-active species is often interpreted to contain thermodynamic dispersion, meaning the population of molecules on the electrode possess a distribution of reversible potential values. Large amplitude ramped Fourier Transformed Alternating Current Voltammetry (FTacV), a technique in which a sinusoidal potential-time oscillation is overlaid onto a linear potential-time ramp, is known to provide access to higher order harmonic components that are largely devoid of non-Faradaic current. Initially, a theoretical study reveals that the use of very large amplitude sinusoidal oscillations reduces the apparent effects of thermodynamic dispersion; conversely, frequency can be varied to change the sensitivity of the measurement to kinetic dispersion. Subsequently, FTacV measurements are used to probe a highly thermodynamically dispersed surface-confined ferrocene derivative attached to a glassy carbon electrode, with amplitudes ranging from 25 to 300 mV and low frequency, which minimises the impact of kinetic dispersion. The results from the experimental study validate the theoretical predictions, demonstrating that we can vary the amplitude in FTacV experiments to tune in and out of thermodynamic dispersion.