Probing the Influence of Counter Electrode Structure on Electrochromic‐Device Operating Potentials and Performance Using Electrochemical Impedance Spectroscopy
Rana Ahmad, Nadia O. Laschuk, Iraklii I. Ebralidze, Olena V. Zenkina, E. Bradley Easton
Abstract
Abstract The paper reports a general methodology for the rational tuning and optimization of electrochromic devices (ECDs) that are based on a monolayer of Fe (II) (4’‐(4‐pyridyl)‐2,2’:6’,2”‐terpyridine) 2 complex (Fe 4’T) covalently embedded onto a screen‐printed high‐surface area indium tin oxide working electrode. We demonstrate that the nature of the counter electrode and the resulting device configuration could drastically improve the long‐term stability of the ECD. We show that the replacement of the flat ITO glass electrode with a high surface area ITO electrode or the use of symmetrical working and counter electrode architecture leads to a much longer performance of the device. We propose a methodology to determine optimal operating conditions for ECDs by fine‐tuning the lower and upper operation potentials. In addition to using traditional cyclic voltammetry (CV), we utilize electrochemical impedance spectroscopy (EIS) to study the intrinsic properties of the devices and understand the factors that define the long‐term cycling stability, which is further described through the use of equivalent circuit models. The main reasoning behind decomposition processes in ECDs and ways to suppress them are discussed.