An Electrochromic Device Based on Prussian Blue, Polymer Matrix Immobilized Viologen, and Ferrocene

Viologens attracted much attention on electrochromic applications for its dramatic optical contrast between its dication state (bleached) and cation-radical state (colored). For the stability concern of eletrochromic device (ECD), solution-type viologen based ECD is necessary to avoid instability. Thus, gel-type electrolytes or immobilized viologens are preferred for solving the long-term instability. In this study, viologen was immobilized on the counter electrode of the ECD by a 3D polymer matrix based gel electrolyte. The polymer matrix with immobilized viologen was fabricated by UV-curing method. Prussian blue (PB) was used as the working electrode of this ECD for its good stability and high contrast ratio. A redox mediator ferrocene (Fc) was added into the ECD to balance the charge between the two electrodes. By doing so, the longer bleaching time of the PB/viologen based ECD (~10 s) was significantly shortened. The working principle of this ECD is sketched in Fig. 1. The PB/Fc/Immobilized viologen based ECD was operated between 1.2 V and -0.8 V. Under this potential bias, the ECD exhibited 61.6% transmittance change (DT%) at 615 nm, and a relatively fast bleaching time of 1.86 s compared to other known PB/viologen based ECD¹, is shown in Fig. 2. The proposed ECD also shows a tunable multi-electrochromism among bleached (-0.8 V), open-circuit voltage (OCV, no potential bias) and colored states (1.2 V).

REFERENCES

(1) Kuo, T. H.; Hsu, C. Y.; Lee, K. M.; Ho, K. C. Sol. Energy Mater.  Sol. Cells 2009, 93, 1755.