Capacitance dispersion in EIS measurements of halides adsorption on Au(2 1 0)

Electrochemical interfaces that display dispersive characteristics do not present the purely capacitive behaviour predicted by the theory of ideally polarised interfaces. For interfaces involving solid electrodes, capacitance dispersion phenomena in the double layer (dl) region are usually attributed to the structural characteristics of the electrode surface as well as to the interfacial region. This paper presents a study of the dispersive characteristics, in the double layer potential region, of interfaces constituted by Au(2 1 0) electrodes and KF, KCl, KBr and KI aqueous solutions. The study was realised by using electrochemical impedance spectroscopy (EIS), with the utilisation of a constant phase element (CPE) to provide an electrical analogue model of the interface. The fitting results are compared with capacitance curves obtained by chronocoulometry, in order to analyse the relationship between the CPE and the interfacial capacitance. For all the systems analysed, evidence for the occurrence of dispersive phenomena in the potential regions associated with phase transition processes (e.g. adsorption and superficial species rearrangement) is observed. On the other hand, in the potential regions where such phenomena do not occur, the interface presents almost pure capacitive behaviour. These observations provide evidence of the strong contribution of the solution properties to the capacitance dispersion.