Understand the Degradation Mechanism of Electrochromic WO3 Films by Double‐step Chronoamperometry and Chronocoulometry Techniques Combined with in situ Spectroelectrochemical Study

• Published in: Electroanalysis (New York, N.Y.) Vol. 29; no. 6; pp. 1573 - 1585
• Main Authors: Zhou, KaiLing, Wang, Hao, Zhang, YongZhe, Liu, JingBing, Yan, Hui
• Format: Journal Article
• Language: English
• Published: 01.06.2017
• Subjects: Chronoamperometry; Chronocoulometry; Degradation; Electrochromism; WO3 film
• ISSN: 1040-0397; 1521-4109
• DOI: 10.1002/elan.201700049

In this paper, we demonstrate that the double‐step chronoamperometry and chronocoulometry techniques are efficient tools for characterizing the basic electrochromic performance of WO3 films (i. e., coloration/bleaching conversion, charge capacity and coloration efficiency). In combination with in situ spectroelectrochemical study, the variations in the optical modulation and charge capacity of the WO3 film under different potential windows were attributed to different ion diffusion depths and the quantity of WO3 sites participating in the redox reaction. Moreover, the double‐step techniques have distinctive advantages for analyzing the cyclic mechanism of the WO3 film. When the inserted Li+ ions in the coloration process cannot be completely extracted from the film in the next bleaching process, these ions accumulate in the film upon cycling, leading to the degradation of the electrochromic performance. Here the accumulated ions are referred to as “unrecoverable ions”. The abundant formation of unrecoverable ions may be due to incomplete reduction of a portion of LixWO3, which is caused by collapse of the Li+ ion diffusion channels in the deep of film after repeated cycles. All these results support that the double‐step chronoamperometry and chronocoulometry techniques have significant advantages to analyze the cyclic stability and explore the degradation mechanism of electrochromic WO3 films.