EIS is also an efficient tool for studying the interface properties of surface modified electrodes. The curve of the EIS includes a semicircle portion and a linear portion. The semicircle portion at higher frequencies represents the electron-transfer limited process
with the linear portion at lower frequencies corresponding to the diffusion process. The impedance spectra of the bare GCE (curve 1) and OMC/GCE (curve 2) are shown in Fig. 2B. The Randles circuit (Fig. 2B inset a) was chosen to fit the impedance data obtained (where Rs represents the Warburg impedance, W, the diffusion impedance, Cdl, the interfacial capacitance). The electron transfer resistance (Rct) at the electrode surface is equal to the semicircle diameter of EIS and can be used to describe the interface properties
of the electrode. And the Rct can be estimated to be 25 X, 519 X at the OMC/GCE and GCE, respectively, indicating the low electron transfer resistance and fast electron-transfer at OMC/GCE (the amplification at higher frequencies was displayed in Fig. 2B inset b).