Extraction of RMS roughness of Pt, Au and graphene electrodes using electrochemical impedance spectroscopy

Abstract

The impedance method is developed for the in-situ determination of electroactive RMS roughness of the electrode for different electrochemical systems. Three electrochemical systems are analyzed to show the wider applicability of this method, viz., (i) rough gold electrode in RTIL medium containing ferrocene, (ii) rough platinum electrode in a mixture of glycerol and water containing potassium ferro/ferricyanide, (iii) drop casted rGO/glassy carbon electrode in aqueous sodium nitrate containing potassium ferro/ferricyanide. The electrochemical impedance spectroscopy (EIS) under reversible electron transfer condition on a rough electrode has an intermediate frequency domain with an anomalous Warburg response. When the diffusion length (\(\sqrt{D/\omega }\)) becomes equal to the RMS roughness at a characteristic frequency (\(\omega _M\)) which is manifested in experimental EIS data as a maximum point in phase angle, where D is the diffusion coefficient of an electroactive species. The frequency range: (\(\omega _M/50 \le \omega \le 5 \,\omega _M\)) represents the anomalously enhanced diffusion which is caused by the trapping of diffusing electroactive molecules in rugged landscape. Additional advantage of this method is explored for determination of unknown diffusion coefficient through equation: \(\sqrt{D_1/\omega _{M1}}=\sqrt{D_2/\omega _{M2}}\), using same electrode in two different media with diffusion coefficient \(D_1\) and \(D_2\). Finally, experimental results shows the resilience of this novel in-situ EIS method for the determination of h and D in different media.