Authors: R. Torres, A. Arnau, H. Perrot, J. García, C. Gabrielli

Journal: Electronics Letters, Vol 42, N. 22, pp 1272-1273 (2006)

 

Requirements for frequency–voltage conversion in alternating current (AC) electrogravimetry are introduced. A new frequency–voltage conversion system based on a double tuning analogue–digital phaselocked loop is proposed. The reported results prove its reliability for AC electrogravimetry measurements.

Introduction: AC electrogravimetry is based on an electrochemical quartz crystal microbalance (EQCM) used in dynamic regime. In EQCM one of the deposited gold electrodes of the quartz crystal resonator can be coated with an electroactive polymer film and can be used as the working electrode (WE) following a classical electrochemical configuration. The frequency shift of the quartz crystal microbalance (QCM) allows obtaining of the mass response associated with the charge transfer, which occurs at polymer=electrolyte interface. AC electrogravimetry was proposed to characterise and separately identify ions and solvent motion at the film=electrolyte interface. In this technique the mass response to a small potential perturbation is analysed in the frequency domain thanks to a fast QCM used in dynamic regime; for that, a continuous voltage with a superimposed small potential sinusoidal perturbation is applied between the reference electrode and the WE of the electrochemical cell. Thus, the so-called electrogravimetric transfer function (EGTF), defined as the ratio (Dm=DE) between the amplitude of induced mass change (Dm) and the perturbation amplitude (DE), can be plotted in a complex plane for the entire range of perturbation frequencies. The various species involved are characterised by a loop in the complex plane and can be separately identified when the loops do not overlap.