Frequency dependence of the phenomenological parameters describing adsorption processes in supercapacitors

It is shown that the frequency dependence of the phenomenological parameters entering Langmuirkinetic equation describing the surface adsorption could be related to a random distribution of relaxationtimes. A theoretical model based on a generalization of Langmuir isotherm, taking into account a ho-mogeneous distribution of relaxation times is proposed for supercapacitor modeling. Its theoreticalpredictions agree well with experimental data derived by the analysis of Lissajousfigures describing theresponse of an electrochemical cell excited with a well defined frequency. According to our data, theeffective desorption time is a rapidly decreasing function of the frequency of the applied signal, whereasthe effective adsorption coefficient is an increasing function of it. The effective relaxation time is inde-pendent of the ionic concentration, whereas the effective adsorption coefficient strongly depends on thisquantity. A large increase in the adsorption coefficient is reported, for the electrochemical cells with highsurface area of the electrodes.