Electrochemical Instability of Flexible Indium Tin Oxide Film: A Time-Resolved Operando Study

Indium tin oxide-coated flexible polyethylene terephthalate (ITO-PET) is increasingly utilized in various electrochemical applications due to its exceptional electrical conductivity and optical transparency. However, the chemical and electrochemical instability of ITO coated on a flexible substrate poses significant challenges to maintaining long-term durability and structural integrity under harsh electrochemical conditions. In this study, we conducted a comprehensive ex situ and operando investigation of the electrical and optical degradation of ITO-PET electrodes in acidic (0.5 M H 2 SO 4 ), neutral (1.0 M KCl), and alkaline (1.0 M KOH) environments by combining liquid-phase atomic force microscopy, time-resolved electrochemical impedance analysis, and time-resolved operando UV–vis spectroelectrochemistry. Our findings reveal that ITO-PET films degrade more severely than ITO glass, with degradation pathways strongly influenced by electrolyte and potential. In acidic conditions, ITO-PET undergoes rapid, catastrophic dissolution within seconds, leading to an immediate loss of both electrical conductivity and optical transparency. Neutral chloride-containing environments induce slower but significant degradation via irreversible anodic dissolution involving indium-chloride complexation, resulting in substantial morphological changes and moderate losses in conductivity and transparency. While neutral KCl solutions cause pronounced electrochemical instability, optical transparency remains relatively stable during short-term cycling. In contrast, under alkaline conditions, degradation behavior is complex, dominated by reversible Sn 2+ /Sn 4+ redox reactions. Despite their electrochemical reversibility, these reactions progressively induce irreversible surface modifications and Sn dissolution, severely compromising optical transparency and electrical conductivity over extended cycling. By integrating real-time multimodal characterization techniques, we provide crucial insights into the degradation mechanisms of ITO-PET film, offering a framework for analyzing and optimizing its durability in practical electrochemical applications.