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Electrochromic Device with Prussian Blue and HPC-based Electrolyte

L.M.N. Assis, R. C. Sabadini, L.P. Santos, J. Kanicki, M. ?apkowski, A. Pawlicka

Small electrochromic devices (ECDs), as shown in the drawing aside, with Prussian blue (PB)/hydroxypropyl cellulose (HPC) electrolyte/CeO₂-TiO₂ configuration were assembled and characterized by electrochemical and spectroscopical methods. Aiming to obtain a deep blue color of the device, electrochromic PB films were deposited galvanostaticaly by applying -0.45 μA for 300 s. The ECDs were assembled by combining the HPC-based transparent membrane between the CeO₂-TiO₂ counter-electrode and the PB layer. The devices switched between transparent and blue states by applying -2.6 and 2.0 V, respectively, and the charge density increased from -6.0 to -8.4 mC cm^-2 when the potentials where applied for 15 and 60 s, respectively. The time of applied potentials also influences the transmittance difference (graph below) between both states that increased from 28 to 32 % when 15 and 60 s potential pulses were applied, respectively. The changes of transmittance in 3 h of open circuit after applying a potential of -2.6 V for 15 s revealed only 1% of transmittance drop, from 60 to 59%. Finally, it was observed that 2,000 chronoamperometric cycling promoted a decrease of the charge density from -6.0 to -1.5 mC cm^-2 and decreased of the difference of transmittance between colored and bleached state from 28 to 5 %.

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