In situ resonance Raman spectroelectrochemical studies of a semisolid redox (I-3(-)/I-) electrolyte encapsulated in a hybrid electrochromic cell

The micro-Raman spectroscopic technique was used to record the resonance Raman spectra of a semisolid redox electrolyte encapsulated in a hybrid electrochromic (EC) cell having the composition WO3 (active EC film)/redox (I-3(-)/I-) electrolyte/Pt (counter electrode). The electrolyte was made from bis end-capped triethoxy silane chemically bonded via the urea groups to a long poly(propyleneglycol) (n = 68) chain precursor. The precursor was catalyzed with acetic or valeric acid while KI and I-2 served as a source of K+ ions and I-3(-)/I- redox pair. The hybrid EC cell was electrochemically cycled between + 2 V (bleached state) and -2 V (colored state) and in the course of cycling the resonance Raman spectra were recorded. The spectra were characterized by a strong symmetric stretching mode of I-3(-) ions at 111 cm(-1) and its intensity changes could serve as a probe to follow the reaction 3I(-) reversible arrow I-3(-) + 2(e)(-) in the EC cell. Variation in intensity of the background scattering with potential was also noted and ascribed to the effect of the reversible precipitation of KI submicrometer crystals on the Raman scattering. The coloring/bleaching changes and the speed and the stability of hybrid EC cells are also reported. (C) 2004 The Electrochemical Society.