Electrospun nanofibers composed of poly(vinylidene fluoride-co-hexafluoropropylene) and poly(oxyethylene)-imide imidazolium tetrafluoroborate as electrolytes for solid-state electrochromic devices

In this work, a novel electrochromic device (ECD), consisting of phenyl viologen (PV) as the cathodically coloring material and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as the stable radical provider for charge balance, was proposed. Nanofibers (NFs) obtained by electrospinning, using poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and poly(oxyethylene)-imide imidazolium tetrafluoroborate (POEI-IBF4), were introduced into the electrolyte to absorb tetrabutylammonium tetrafluoroborate and propylene carbonate, so as to form a solid-state electrolyte for the ECD. The NFs were characterized by distribution of their diameters, or histograms, based on the scanning electron microscope (SEM) images; their physical properties, including electrolyte uptake, ionic conductivity, and porosity were studied. The proposed ECDs were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), UV-visible spectra, and dynamic transmittance curves. The pertinent N15P10-ECD exhibited a high transmittance change (ΔT) of 68.7% at 590 nm, while maintaining a good cycling stability (95.5% of its original ΔT) after continuous 1000 switching cycles of operation at room temperature.