Prussian blue for electrochromic devices

• The membranes were prepared by solvent casting method.
• Prussian blue (PB) as electrochromic layer and ionic conductive membrane
• Natural macromolecules as solid electrolyte in new ECDs development

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 ΔTVIS = 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 ΔTVIS 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 ΔTVIS 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.