Complementary AC Voltammetry—A Method for Simultaneous Measurement of Faradaic and Nonfaradaic Currents in an Electrochemically Reversible System

Abstract

We report a technique named complementary alternating current voltammetry (CACV) to simultaneously measure faradaic and nonfaradaic currents in an electrochemical sensing apparatus using three sequential input potential waveforms: i) a triangular waveform as used in cyclic voltammetry (CV); ii) small signal sine modulated triangular waveform; and iii) small signal cosine modulated triangular waveform. The three output currents were post-processed to obtain the peak faradaic current ‘ $I_{Fp}$ ’ (sensitive to the concentration of the analyte) and nonfaradaic current ‘ $I_{NF}$ ’ (sensitive to the equivalent circuit parameters of the electrochemical cell). The proposed method has the advantage of producing a straight baseline $I_{NF}$ which is not easily possible in CV and measure $I_{Fp}$ without using a phase lock-in amplifier (commonly used in AC voltammetry). The proposed method was computationally investigated using finite difference time domain method and experimentally validated for a standard redox reaction of potassium ferricyanide using a homemade digital potentiostat. CACV showed the successful recovery of faradaic and nonfaradaic currents, even for the cases where CV analysis was not possible due to the low faradaic-to-nonfaradaic current ratio. Finally, we observed that there was change in the peak current with a change in concentration as well as temperature, whereas change in the baseline was only due to the change in temperature. We believe that this can be used for calibration of an electrochemical cell to sense analytes or to compensate for any change in currents in a fixed analyte concentration due to extraneous parameter changes.