Impedance of a rotating disc electrode with a reversible reaction

Abstract

This paper presents a model of electrode impedance for the case of a fast reversible reaction. The various contributions of the impedance were analysed with particular emphasis on the charge transfer resistance: this resistance was shown to be also dependent on mass transfer phenomena. For the case of significant mass transfer control, the diameter of the high-frequency loop increases with the absolute value of the overpotential. The various physicochemical parameters involved in the expression for impedance were determined through previous measurements. The impedance model was validated by experimental measurements carried out with the hexacyanoferrate (II)-(III) couple on a Pt RDE. List of symbolsD diffusion coefficient (m 2 s À1 ) E potential (V) F faradaic constant = 96 487 C mol À1 f F=ðRTÞ(V À1 ) i current density (A m À2 ) i 0 exchange current density (A m À2 ) I current (A) j imaginary number ( j 2 ¼ À1) m average of the relative deviation n constant phase element (CPE) parameter N number of frequencies in spectra Q specific generalised capacitance (X À1 s n cm À2 ) r specific resistance (X m 2 ) R gas constant (8.314 J K À1 mol À1 ) R resistance (X) R e cell resistance (X) s Laplace variable (s À1 ) t time (s) T temperature (K) x distance from the electrode surface (m) [X] concentration of species X (mol m À3 ) z specific impedance (X m À2 ) Z impedance (X) Z 0 real part of the impedance (X) Z 00 imaginary part of the impedance (X)Greek symbols a charge transfer coefficient d thickness of the diffusion layer (m) g electrode overpotential (V) q density of the solution (kg m À3 ) m kinematic viscosity of the solution (m 2 s À1 ) x signal pulsation (rad s À1 ) X angular velocity of the electrode (rad s À1 )

Nonlinear Frequency Response Analysis of the Ferrocyanide Oxidation Kinetics. Part II. Measurement Routine and Experimental Validation

“…The high-frequency loop, magnified in Figure b, is usually assigned to charge-transfer resistance and the low-frequency loop to mass transfer limitations . The presence of the high-frequency loop is not always reported in literature; for example, Boillot et al observed only a part of the high-frequency semicircle, probably because of relatively low higher frequency limit (10 kHz in comparison with 65 kHz in the present study). A well-developed high-frequency loop was also observed by Campbell and Peter, who applied large-amplitude input current around open circuit potential for the same reaction on Au.…”

Nanostructured Fe-N-C as Bifunctional Catalysts for Oxygen Reduction and Hydrogen Evolution

“…In the equivalent circuit (EC), R1 represents ohmic resistance, R2 represents charge transfer resistance, and Q2 represents a constant phase element related to double layer capacitance (Q2). According to this EC, charge transfer limits the reaction kinetics [65][66][67], while mass diffusion is limited to a finite and narrow layer. A short Warburg diffusion element (W) was added to model the low-frequency process related to diffusion phenomena.…”

Electrochemical corrosion behavior of Al7075 rotating disc electrode in neutral solution containing l-glutamine as a green inhibitor

“…The electroactive species simply diffuse through NDL to reach the surface of the electrode. In this case, the Nyquist plots have an asymmetrical shape called ''finite length diffusion'' [36,37]. Such an asymmetrical shape was also seen in the Nyquist plots obtained for corrosion of Al7075 in 3.5% NaCl solution at rotation speeds of higher than 500 rpm (Fig.…”

“…In some systems like RDE, there is a region close to the electrode surface in which mass transport occurs only by diffusion being called ''Nernst diffusion layer'' or NDL [36,37]. Outside the NDL region, the solution is homogeneous due to the stirring produced by the rotating electrode assembly.…”