Molecular-level manipulation of V2O5/polyaniline layer-by-layer films to control electrochromogenic and electrochemical properties

This work describes how manipulation at the molecular level of V2O5/polyaniline (PANI) nanocomposites built with the layer-by-layer (LBL) technique promotes enhancement of charge storage capability, new electrochromic effects, and control of ionic flux. By changing the film architecture we control the amount of PANI participating in the redox processes of the LBL films. As a consequence, the films display the electrochemical profile of V2O5 and the chromogenic properties of PANI. Impedance spectroscopy data show the presence of distinct phases in the nanocomposite, which allows a conducting path for the whole potential range between 0.5 and -1.5 V. Further control of the properties of the nanoarchitectures is achieved by adsorbing V2O5/PANI LBL films onto a cast PANI film. By changing the time of immersion of the PANI-V2O5/PANI system into a solution of LiClO4/propylene carbonate (PC), we were able to monitor the mass gain/loss (Deltam) with an electrochemical quartz crystal microbalance (EQCM) as a function of charge (q) and control the intercalating/deintercalating species. The Deltam/q ratio shifted from 0.77 to -0.12 mg C-1 when a 10-bilayer LBL film was immersed into a solution of LiClO4/PC during 24 h, indicating a change from an anionic contribution to a cationic one for the charge compensation process. It is envisaged that the molecular-level control demonstrated here may be exploited in producing efficient lithium batteries as well as electrochromic devices and sensors.