Frequency dependence of the phenomenological parameters describing adsorption processes in supercapacitors

It is shown that the frequency dependence of the phenomenological parameters entering Langmuir kinetic equation describing the surface adsorption could be related to a random distribution of relaxation times. A theoretical model based on a generalization of Langmuir isotherm, taking into account a homogeneous distribution of relaxation times is proposed for supercapacitor modeling. Its theoretical predictions agree well with experimental data derived by the analysis of Lissajous figures describing the response of an electrochemical cell excited with a well defined frequency. According to our data, the effective desorption time is a rapidly decreasing function of the frequency of the applied signal, whereas the effective adsorption coefficient is an increasing function of it. The effective relaxation time is independent of the ionic concentration, whereas the effective adsorption coefficient strongly depends on this quantity. A large increase in the adsorption coefficient is reported, for the electrochemical cells with high surface area of the electrodes. •Evidence of frequency dependence of the parameters entering Langmuir kinetic equation describing surface adsorption.•The desorption time is a decreasing function of the frequency, the adsorption coefficient is an increasing function of it.•Generalization of the theory for linear systems, with a response function given by a distribution of relaxation times.•Modeling the supercapacitor response to an harmonic excitation of small amplitude, where the electrodes are blocking.