Influencing factors on electrochromic hysteresis performance of ruthenium purple produced by a WO3/Tris(2,2′-bipyridine)ruthenium(II)/polymer hybrid film

Abstract

Abstract A [Ru(bpy) 3 ] 2+ (bpy = 2,2′-bipyridine)/WO 3 hybrid (denoted as Ru-WO 3 ) film was prepared as a base layer on an indium tin oxide electrode by electrodeposition from a colloidal solution containing peroxotungstic acid, [Ru(bpy) 3 ] 2+ and poly(sodium 4-styrenesulfonate). A ruthenium purple (RP, Fe III 4 [Ru II (CN) 6 ] 3 , denoted as Fe III -Ru II ) layer was electrodeposited on a neat WO 3 film or a Ru-WO 3 film from an aqueous RP colloid solution to yield a WO 3 /RP bilayer film or a Ru-WO 3 /RP bilayer film, respectively. The spectrocyclic voltammetry measurement reveals that Fe II -Ru II is oxidized to Fe III -Ru II by a geared reaction of [Ru(bpy) 3 ] 2+/3+ and Fe III -Ru II is reduced by a geared reaction of H x WO 3 /WO 3 in the Ru-WO 3 /RP film. These geared reactions produced electrochromic hysteresis of the RP layer. However, the absorbance change in the hysteresis was smaller than that for the Ru-WO 3 /Prussian blue bilayer film reported previously, resulting from the lower electroactivities of any redox component for the Ru-WO 3 /RP film. The lower electroactivities could be explained by the specific interface between the Ru-WO 3 and RP layers. It might contribute to either an increase of the interfacial resistance between the Ru-WO 3 and RP layers, or formation of the physically precise interface between the layers to make it difficult for counter ions to be transported in the interfacial liquid phase involved in the redox reactions in the film. The specific interface at the Ru-WO 3 and RP layers could be formed possibly by the electrostatic interaction between [Ru(bpy) 3 ] 2+ and terminal [Ru(CN) 6 ] 4− moieties of RP. It could be suggested by the decreased redox potential of [Ru(bpy) 3 ] 2+ in the Ru-WO 3 layer from 1.03 to 0.61 V by formation of the RP layer.