Frequency Responses of Molar Electrochemical Peltier Heat and Entropy Changes Analyzed as Thermometric Transfer Functions

In honor of Prof. Dr. Fritz Scholz in his recent retirement. This work proposes a theoretical framework to obtain the frequency response of molar electrochemical Peltier heat and entropy changes induced by a modulated electrical signal. This is based on an internal energy balance developed for a working electrode thermistor in ac regime. Then, from an analysis that correlates the electrochemical impedance and the interfacial temperature variation, two new transfer functions that depend on the frequency ω , named as entropy changes Δ S ω , and molar electrochemical Peltier heat, Π ω are obtained. This strategy is tested in two electrochemical systems: the ferrocyanide/ferricyanide couple and the copper ions in an acid sulphate-chloride medium. Both systems are analyzed by dc thermometric measurements, electrochemical impedance spectroscopy and ac -thermometric experiments namely variation of interfacial temperature. As a result, Δ S ω and Π ω , are obtained and their values are correlated to the relaxation processes involved in the electrochemical reaction. Additionally, a brief discussion is included concerning the differences between the classical dc thermoelectrochemical methodology and the proposed approach here.