Noise spectra of K⁺ and NH₄⁺ ions at over-limiting current in an electrochemical system with a cation exchange membrane

The present work investigates the effect of the counter ion nature on the noise of the over-limiting current (Iov). Moreover, the electrochemical methods, current voltage curve (I–V) and the chronopotentiometry (V–t) measurements are applied. The over-limiting current is always accompanied by a neat electrical noise. It is a well accepted experimental phenomenon. The study of this noise may contribute to a better understanding of the Iov and the feasibility of electrodialysis operation at this current in terms of energy consumption. The electrical noise depends directly on the counter ion nature. The power spectral density of the membrane's potential fluctuation was obtained via Fourier analysis of the time series recorded during the transport of counter ions (K⁺ and NH₄⁺). The spectra are evaluated above the limiting current indicating the differences between the K⁺ and the NH₄⁺. It is found that the cation NH₄⁺ presents a singular behaviour and the noise is minimal.