Even after decades of development, the widespread application of electrochromic windows (ECW) is still seriously restricted by their high price and inadequate performance associated with structural/fabrication complexity and electrochemical instability. Herein, a simple hybrid electrochromic system based on PFSA (perfluorosulfonic acid)-coated Prussian blue (PB, Fe4III [FeII(CN)6]3) film and Ferricyanide-Ferrocyanide ([Fe(CN)6]4-/[Fe(CN)6]3-)-containing hybrid electrolyte is reported. The PB film and the [Fe(CN)6]4-/[Fe(CN)6]3- couple show near redox potentials well inside the electrochemical window of water, resulting in a low driven voltage (0.4 V for coloring and -0.6 V for bleaching) and a relatively long lifespan (300 cycles with 76.9% transmittance contrast retained). The PFSA layer, as a cation-exchange structure, significantly improves the transmittance modulation amplitude (ΔT: 23.3% vs. 71.9% at a wavelength of 633 nm) and optical memory abilities (ΔT retention: 10.1% vs. 67.0% after 300 s open-circuit rest increases) of the device, by means of preventing the direct contact and charge transfer between the PB film and the [Fe(CN)6]4-/[Fe(CN)6]3- couple. This "hybrid electrolyte + electron barrier layer" design provides an effective way for the construction of simple structured electrochromic devices.
Keywords: Prussian blue; [Fe(CN)6]4−/[Fe(CN)6]3− redox couple; electrochromic; perfluorosulfonic acid ion-exchange membrane; smart window.