Immobilisation of phosphomolybdic (PM) acid by Nafion and the electrochromism of the resulting PM-Nafion films

Abstract

The electrochromism of phosphomolybdic (PM) acid in solution and immobilised in Nafion has been investigated. Immobilisation made use of two simple dip-coating techniques which allowed easy modification of the electrochemical activity of the composite films. PM in solution changed from light yellow to blue upon reduction, whereas immobilised PM showed a change from pale yellow to light blue under identical conditions. Electrostatic repulsions between PM anions and negatively charged sulfonic groups in Nafion limited the amount of PM that could be molecularly dispersed in Nafion. This, coupled with the poor conductivity inherent in the Nafion matrix, resulted in suppressed electrochemical reactivities for the composite films. Despite these results, UV-VIS absorption spectra showed marked differences in light absorption between the pristine and coloured forms of immobilised PM, indicative of application potentiality.