Evaluation of Reaction Property of Anodized Carbon Electrode by Electrochemical Impedance Spectroscopy

Anodic oxidation of carbon fabricated on an FTO-glass electrode was done to improve the electrochemical active area of the carbon electrode, which is anticipated for use as a platinum-free counter electrode of Dye-sensitized Solar Cells (DSCs). The electrochemical properties of the carbon electrode with various anodizing times were investigated using electrochemical impedance spectroscopy (EIS). The impedance spectra of the dummy cell, which was composed of the platinized FTO glass for the anode and the anodized carbon electrode for the cathode, were measured to evaluate the effects of the anodic oxidation time on the carbon electrode electrochemical properties. Results of the impedance spectra showed that the loop related to the carbon/FTO-glass in the middle frequency range was changed because of the carbon electrode anodizing time. The electric double layer capacitance of the carbon electrode (Cdl,c) was increased gradually during anodic oxidation for 2 min; then it decreased drastically. However, the charge transfer resistance of the carbon electrode (Rct,c) decreased until 2 min-anodic oxidation; then it increased again. The XPS analysis results showed that the O1s peak of the carbon electrode exhibited high intensity when the anodic oxidation times were 2 and 3 min. These results demonstrate that the oxygen function formed on the carbon electrode by anodic oxidation of the carbon electrode affected the reaction activity on the carbon electrode.