A Study of Depletion Layer Effects on Equivalent Circuit Parameters Using an Electrochemical Quartz Crystal Impedance System

Abstract

An electrochemical quartz crystal impedance system (EQCIS) was used to investigate depletion layer effects on equivalent circuit parameters of piezoelectric quartz crystal resonance in electrochemical processes of CoSO4 aqueous solutions containing 0.4 mol/L ethylenediamine + 0.5 mol/L Na2SO4, 0.2 mol/L 1,10-phenanthroline + 0.5 mol/L Na2SO4 and K3Fe(CN)6, or K4Fe(CN)6 aqueous solutions containing 1.0 mol/L KCl in potential cycling experiments, respectively. The impedance data were analyzed according to Martin's model. For the former two systems, motional resistance R 1, series resonant frequency f s, and motional inductance L 1 changed reversibly with potential, and the observed values of ΔR 1, ΔL 1, and Δf s roughly satisfied equations reflecting liquid loading effects, suggesting that changes in these parameters might be mainly governed by local variations in solution density and viscosity near the electrode surface. For the latter two systems, reversible changes in R 1 with potential coincided well with the simulated results from variations in solution density and viscosity near the electrode surface; however, besides reversible changes of ΔL 1 and Δf s with potential, rising drifts of f s and decreasing drifts of L 1 were found at oxidation potentials. The drifts of f s and L 1 observed are believed to result from mass changes of the gold electrode, and cyanide and chloride corrosion of the gold electrode at oxidation potentials may play an important role for the drifting phenomena. It is concluded that quantitative analyses of ΔR 1, ΔL 1, and Δf s obtained from the EQCIS provide the possibility for differentiating the net depletion layer effect with the change in electrode mass, and the ΔR 1 response may be well used for evaluating local changes in liquid loading inside the depletion layer compared with responses of Δf s and ΔL 1.

A Comparative Study on the Viscoelasticity and Morphology of Polyaniline Films Galvanostatically Grown on Bare and 4-Aminothiophenol-Modified Gold Electrodes Using an Electrochemical Quartz Crystal Impedance System and SEM

“…R1, C0 and two parameters among L1, 1/C1 and f0. The G and B equations of the BVD model used for the fitting are given as follows:where ω = 2πf, U = ωL1 -1/(ωC1) = (1/C1)(ω/ω0 2 -1/ω), ω0 = 2πf0, and Y is the admittance of the PQC resonance.In addition, the following five characteristic frequencies of the PQC resonance and the half peak width of the conductance peak (∆fG1/2) were mentioned and used previously: [7][8][9][10][11] (2) The equivalent-circuit parameters of the 9-MHz piezoelectric quartz crystal (PQC) resonance were measured in situ during the galvanostatic polymerization of aniline on 4-aminothiophenol(4-ATP)-modified and bare Au electrodes for ca. 2000 s, respectively.…”

“…1 Compared with the conventional EQCM that generally records the oscillation frequency shift of a piezoelectric quartz crystal (PQC), the electrochemical quartz crystal impedance system (EQCIS) allows a simultaneous and rapid measurement of electroacoustic impedance (or admittance) data of the PQC resonance during electrochemical perturbations, and can thus provide direct insight into the foreign film rigidity through analyzing multidimensional piezoelectric information that characterize the PQC resonance very completely. [2][3][4][5][6][7][8][9][10][11] The PQC impedance has been analyzed based on a Butterworth-Van Dyke (BVD) equivalent electrical circuit composed of a motional arm and a static arm in parallel. [1][2][3][4][5][6][7][8][9][10][11][12][13] The motional arm contains three equivalent circuit elements in series: the motional resistance (R1), the motional inductance (L1) and the motional capacitance (C1), while the static arm contains only the static capacitance (C0), and each equivalent circuit parameter has its distinct physical meaning.…”

“…[2][3][4][5][6][7][8][9][10][11] The PQC impedance has been analyzed based on a Butterworth-Van Dyke (BVD) equivalent electrical circuit composed of a motional arm and a static arm in parallel. [1][2][3][4][5][6][7][8][9][10][11][12][13] The motional arm contains three equivalent circuit elements in series: the motional resistance (R1), the motional inductance (L1) and the motional capacitance (C1), while the static arm contains only the static capacitance (C0), and each equivalent circuit parameter has its distinct physical meaning. [1][2][3][4][5][6][7][8][9][10][11][12][13] The equivalent circuit parameters can be obtained by the simultaneous fitting of the experimental data of the conductance (G) and susceptance (B) of the PQC resonance to the BVD model.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] The equivalent circuit parameters can be obtained by the simultaneous fitting of the experimental data of the conductance (G) and susceptance (B) of the PQC resonance to the BVD model. [7][8][9][10][11] Four independent parameters are obviously required as estimation parameters during the fitting: e.g. R1, C0 and two parameters among L1, 1/C1 and f0.…”

“…In addition, the following five characteristic frequencies of the PQC resonance and the half peak width of the conductance peak (∆fG1/2) were mentioned and used previously: [7][8][9][10][11] (2) (3) s 2 = (2 f s ) 2 ω π…”