An electrochromic device based on Prussian blue, self-immobilized vinyl benzyl viologen, and ferrocene

In this study, the electrochromic property of vinyl benzyl viologen (VBV) was first investigated and incorporated in an electrochromic device (ECD). The polymerizable vinyl moiety of VBV enables a self-immobilization through UV-curing under potential bias. Immobilized VBV (I-VBV) was obtained on the electrode and grafted with polymer electrolyte. An ECD consisted of Prussian blue (PB), I-VBV, and ferrocene (Fc) was fabricated (PB/Fc/I-VBV ECD) in which Fc acted as a redox mediator. With the utilization of polymer electrolyte, Fc, and immobilization of VBV, the proposed PB/Fc/I-VBV ECD with a UV-curing time of 40 s (PB/Fc/I-VBV-40) exhibited the best cell performance among all conditions in terms of long-term stability. It gives 60.6% transmittance change (δT) at 615 nm initially when switched between 1.2 V and -0.8 V. Short bleaching and coloring times of 1.32 s and 2.13 s were achieved respectively. Moreover, good long-term stability was obtained, maintaining 86.5% of its original δT after 10,000 cycles. The PB/Fc/I-VBV ECD also exhibited a unique memory characteristic among all viologens-based ECDs reported in literatures and allowed the possibility for tuneable multi-electrochromism.