Maintaining Electrochemical Performance of Flexible ITO-PET Electrodes under High Strain

Flexible electrode materials, particularly indium tin oxide (ITO)-coated polyethylene terephthalate (PET), have attracted the attention of researchers for a wide variety of applications. However, there has been limited attention to the effects of electrode flexibility during electrochemical processes. In this research article, we studied how bending commercially available ITO-PET electrodes impacts the electrodeposition process of polyaniline (PANI). Thicker ITO layers start cracking at a normalized strain of 0.10 (bending radius of 10 mm), and cracking becomes detrimental to full deposition at a normalized strain of 0.16 or higher (bending radius of 6 mm or lower). Thinner ITO layers were evaluated as electrodes in electrochemical applications; however, the higher resistance of these electrodes prevented uniform electrodeposition of PANI. In order to overcome the issues of cracking, conductive thin films and copper tape were explored as low-cost methods for electrically bridging cracks in the electrode. While conductive thin films reduced the resistance effect, copper tape was found to fully restore the original electrochemical activity as measured by chronoamperometry and enable uniform electrodeposition at a bending radius as low as 3 mm. This strategy was then demonstrated by performing electrochromic bleaching of PANI under high-strain conditions. These studies illustrate some of the limitations of ITO-PET electrodes and strategies for overcoming these limitations for future applications that require a high degree of flexibility in a transparent electrode substrate.