A Study on an Electrochromic Device based on Viologen and Prussian Blue

• Main Authors: Chiao-Fen Lin, 林巧芬
• Other Authors: Kuo-Chuan Ho
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/56210141974992265391

碩士 === 國立臺灣大學 === 化學工程學研究所 === 91 === In this study, a new electrochromic system was developed. A hybrid type complementary electrochromic device (ECD) based on heptyl viologen (HV) solution and Prussian blue (PB) thin film exhibits blue-to-colorless electrochromism. The HV-PB electrochromic device is designated as HPECD. The main motivation of this research is to develop a complementary ECD possessing a high contrast, good cycling stability, and suitable for real application. The electrochemical and optical properties of the electrochromic materials were analyzed by cyclic voltammetry, potential step, and chronopotentiometry methods, in conjunction with in situ UV-VIS spectrophotometry. The obtained properties were used to find the proper operating conditions for the assembled HPECD. The HPECD was also studied by the same techniques mentioned above to evaluate its performance. This work begins with the determination of the solvent by studying the cycling stability of PB in different organic solvents. Propylene carbonate (PC) was chosen as the solvent in this study by considering both the cycling stability of PB thin film and the safety of the ECD. Then the fundamental properties of HV and PB were studied. Heptyl viologen, a cathodically coloring material, displays colorless in its anodic state (0V vs. Ag/Ag+) and becomes blue at -1.1V (vs. Ag/Ag+). As for the optical properties, the largest absorbance modulation of HV appears at 605 nm. Prussian blue, an anodically coloring material, shows blue in its anodic state (0.3V vs. Ag/Ag+) and reduces to the colorless Everitt’s salt (ES) (-0.9V vs. Ag/Ag+). The absorbance modulation of PB exists the largest value at 730 nm. Therefore the ECD consists of HV and PB exhibits a good compatibility in color. After characterizing the individual electrode, we investigated and analyzed the HPECD extensively. A safe operating voltage range with high contrast and good cycling stability was determined by changing the operating voltage. Moreover, by decreasing the cell gap of the HPECD, the resistance of the electrolyte solution (i-R drop) can be decreased, so does the bleaching time be shortened. In addition, by changing the cations in the supporting electrolyte, it was found that the HPECD with K+ in the supporting electrolyte has the largest transmittance modulation, the fastest response time, and the best cycling stability. Finally, the performance of the HPECD with K+ as the supporting electrolyte was discussed. The steady-state relationship between the transmittance and the applied cell voltage was obtained. Depending on the need, the ECD can be darkened in different depths by choosing various operating cell voltages. Therefore, the HPECD possesses high competitiveness. When applying the bleached voltage of 0V and the darkened voltage of 1.0V, it had a transmittance modulation of ca. 70% and maintained 96% of its original value after 50,000 continuous cyclings. The coloration efficiency of the HPECD was ca. 250 cm2/C at 609 nm.