An Alternative Method to Calculate the Harmonic Components from Electrochemical Frequency Modulation Data Using Polynomial Fitting

The Electrochemical Frequency Modulation (EFM) technique applies a potential signal consisting of two sinusoids of the same amplitude and different frequencies to a corroding system. The analysis of the nonlinear components at harmonic and intermodulation frequencies of the system's response can give information about the corrosion behavior, such as Tafel slopes and corrosion current. These components are usually computed using the Fast Fourier Transform (FFT) algorithm on the current response. This work proposes an alternative method for computing the harmonic components from EFM data. The proposed method uses a polynomial fitting for modeling the current response of the electrochemical system in order to calculate the harmonic components analytically. The method was evaluated by processing theoretical data based on the Butler-Volmer equation. Results indicate that a polynomial fitting of fifth order can give a good approximation of the Tafel constants and corrosion current. Additionally, the method was tested on experimental data from a three-electrode system consisting of an AISI 316L working electrode, platinum counter electrode and Saturated Calomel Electrode (SCE) as the reference electrode in a 1 molL-1 NaCl solution. Results suggest that using polynomial fit could reduce estimation error.