Characterization of ac Voltammetric Reaction−Diffusion Dynamics:  From Patterns to Physical Parameters

Despite the widespread use of electrochemical sensing techniques, the determination of the physical parameters from the current response of rapid voltammetric measurements has been difficult for two reasons: large capacitance contributions overwhelm the current response of transient measurements and the reaction dynamics are inherently nonlinear and nonstationary. In this work, we present a signal processing methodology that in combination with a large-amplitude/high-frequency voltage waveform method, ac voltammetry, is able to determine the underlying physical parameters in heterogeneous electrochemical reaction−diffusion processes. Through a large number of numerical calculations, we explore the effect of kinetic, thermodynamic, and mass transport parameters on two components of the current response, the even and the odd. We study the even component directly whereas for the odd component, which is considerably influenced by capacitance, we use the Hilbert transform, which is suitable for the analysis of nonstationary and nonlinear data sets, to minimize the capacitance contribution. The theoretical analysis is applied to measurements of well-characterized electrochemical reactions, Ru(NH3)6 2+/3+ and Fe(CN)6 4-/3-, using two different electrode materials, glassy carbon and platinum, and the physical parameters deduced are in excellent agreement with published results.