Prussian blue for electrochromic devices

Abstract

All solid electrochromic devices (ECDs) were prepared using Prussian blue (PB) as electrochromic layer, CeO2 -TiO2 as counter electrode, and either DNA-Er(CF3SO3)3 or Agar-Eu(CF3SO3)3 as ionic conductive membrane. The ECDs were assembled by combining the natural macromolecule-based electrolyte membrane placed between the glass-ITO/PB and CeO2-TiO2/ITO-glass electrodes. The two kind of electrochromic devices were characterized electrochemically and spectroscopically. The electrochemical measurements revealed that applying potentials of −3.0 and +2.0 V promoted the color change of the ECD from blue to transparent. The highest contrast of ΔT VIS = 25 ± 2% was at 686 nm after 60 s of applied potential for ECD with DNA-Er3+-based electrolyte. This ECD showed the charge density of −5.1 mC cm−2 after 15 s and −10.4 mC cm−2 after 60 s of potential application. Although a successive chronoamperometric (CA) cycling showed the insertion/extraction processes uniform, the ΔT VIS and charge density values dropped down to 5% and −1.6 mC cm−2 after 1000 CA cycles, respectively. The ECD with Agar-Eu3+-based electrolyte displayed almost the same charge density values of −5.1 mC cm−2 after 15 s and −10.5 mC cm−2 after 60 s of −3.0 V potential application. This value decreased to −1.1 mC cm−2 after 1400 CA cycles. The best result of ΔT VIS was of 35 ± 2% at λ = 686 nm. All the presented results suggest the possibility of using PB as electrochromic coating and natural macromolecules as solid electrolyte in new ECDs development.