Improved electrochromic performance of viologen at an ITO-nanoparticle film electrode

An ITO (indium-tin-oxide)-nanoparticle film electrode was prepared by applying an ITO nanoparticle-dispersed solution to an ITO planar plate and then sintering it. The electrochromic properties of 1,1′-dibenzyl-4,4′-bipyridinium (DBV2+) were examined at the nanoparticle film electrode. The one-electron reduction of DBV2+ produced a filmy purple deposit of DBV+, and electrochromism between the white and purple appeared. An incomplete vanishing (ghost image), which often occurs when an ITO planar electrode is used, was not observed at the nanoparticle film electrode. The successful ghost-free electrochromism was explained in terms of the much lower molecular density of the deposited DBV+ per unit real surface area compared to that on the ITO planar electrode. Also, it was demonstrated that the coloration–decoloration cycle was significantly improved by the effect of the ghost-free electrochromism.