Harmonic distortion at the electrode/electrolyte interface: A physical interpretation of Schwan's empirical model

This paper concerns the modelling and interpretation of the non-linear harmonic behaviour of biomedical electrode/electrolyte interfaces. For the first time a physical interpretation of the published work on this phenomenon by Schwan and his colleagues (1999) is given. Higher order harmonics were calculated based on the assumption that the non-linearity of the interfacial impedance is dominated at low frequencies by the faradaic charge transfer resistance which shunts the relatively linear non-faradaic double layer capacitance. The dependence of harmonic components on the applied signal amplitude was compared between (i) a model based on the Butler-Volmer equation and (ii) Schwan's experimental and empirical results. A good agreement was found, between the theoretical model and Schwan's empirical observations.