Electrochromism and redox switching of cobalt hexacyanoferrate–polyaniline hybrid films in a hydrophobic ionic liquid

Electrochromic hybrid thin films of cobalt hexacyanoferrate–polyaniline (CoHCF–PAni) have been synthesized by forming a film of K2Co2+[Fe2+(CN)6] followed by electropolymerization of PAni from an aqueous micellar solution. The hybrid film structure comprises cube like shapes with a face centered cubic lattice of CoHCF and fibers of PAni. Electrochemistry of hybrid films followed for the first time in an ionic liquid—1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, revealed significant differences in their electrochromic and redox parameters in comparison with those observed for neat CoHCF and PAni films. Charge transfer, capacitive and diffusive phenomena were found to be controlled by the film microstructure, applied potential and the ingress–egress ability of the pyrrolidinium cation. The high coloring efficiency of 262 cm2 C−1 at 687 nm under +0.4 V shown by the hybrid film and its ability to sustain 1000 cycles without much loss in optical contrast renders it suitable for use in electrochromic smart windows.