Long-term stability of nanostructured polypyrrole electrochromic devices by using deep eutectic solvents

To overcome the major drawback involved in the electrochromic behavior of conducting polymers in traditional aqueous electrolytes, it is important to use novel electrolytes that are eco-friendly and highly stable. Tiron doped polypyrrole (PPy-Tiron) film was electrochemically coated onto FTO/glass surface with the purpose of yielding uniform, transparent and adherent film. Scanning electron microscopy (SEM), cyclic voltammetry and spectroelectrochemical methods were used to characterize the resultant polymer. The effect of different deep eutectic solvents (DESs) choline chloride (ChCI) based ionic liquids such as ChCl/urea, ChCl/ethylene glycol (EG) and ChCl/glycerole (Gly) on the spectroelectrochemistry and electrochromic features of electropolymerized polymer has been investigated and we found a very significant solvent effect. The cyclic stability studies reveal that the PPy film has much more electrochemical and optical durability in DESs than those of conventional solvents. The maximum optical contrast was measured after 560 deep double potential steps as 61% for the PPy-Tiron film in ChCl/urea. By employing DES as electrolyte, the polymer retained 99% of its electroactivity after 500 potential cycles, showing enhanced stability.