Structure and electrochromic properties of polypyrrole films synthesized by AC electrochemical impedance spectroscopy under different amplitude

Alternating current (AC) electrochemical impedance spectroscopy (EIS) was employed to synthesize polypyrrole (PPy) electrochromic films on fluorine-doped tin oxide (FTO) transparent conductive glasses. When depositing the PPy films, a fixed initial voltage was 700mV and AC of different amplitudes was applied. The influence of AC voltage amplitude on the structure and electrochromic performance of PPy films was investigated. Scanning electron microscope (SEM) observation reveals that the PPy films prepared under AC are composed of uniform-distributed nanospheres when the AC amplitude is below 400mV, which is different from the submicron structure displayed by PPy films prepared under direct current (DC). This kind of nanospherical structure is helpful to ion transport, resulting in improved electrochromic properties of the PPy films prepared under AC compared with the PPy film prepared under DC. In particular, the PPy film prepared under 100mV amplitude AC shows ideal electrochromic properties, with an ion diffusion coefficient of 8.13 × 10−10 cm2·s-1, a coloring efficiency of 137.4 cm2·C-1, quick coloration and bleaching switching times of 5.0s and 6.5s, respectively, and retains 65.7% of its optical modulation after 100 cycles.