Comments on the Article 'An Electrochemical Impedance Measurement Technique Employing Fourier Transform' by J.-S. Yoo and S.-M. Park

摘要

In the recent article, Yoo and Park presented a new technique of impedance measurements using discrete time Fourier transform, DTFT, of the derivative of current, di/dt, after application of a small potential step. The authors measured the transient current up to (n_(0)+1)Δt, where n_(0)+1 is the number of points sampled and Δt is the sampling time. They assumed that for longer times, the current and its derivative are equal to zero. Then, they reconstructed the whole frequency spectrum, even for very low frequencies (assuming that i=0 for t>(n_(0)+1)Δt). The problem with this method is that in the measured current i(t) there is no information about lower frequencies, as i(t>(n_(0)+1)Δt)=0. The authors simply extrapolate the information obtained at short times (or high frequencies) to low frequencies. The statement that "our method would allow possible measurements of impedance data between the half of the highest frequency down to almost dc" by carrying out the experiments in a very short time period (n_(0)+1)Δt is not true.