Electrochromism

About: Electrochromism is a research topic. Over the lifetime, 13097 publications have been published within this topic receiving 294637 citations.

Electrochromism in Anodic Iridium Oxide Films II . pH Effects on Corrosion Stability and the Mechanism of Coloration and Bleaching

Abstract: The oxidation state of iridium ions in an oxide film, grown electrochemically on an Ir metal reflector electrode, can be rapidly and reversibly modulated according to the electrochromic redox reactionBy suitable choice of electrolyte composition and potential limits, the coloration and bleaching processes can be effected without causing oxide film growth or dissolution, or electrolyte decomposition. Color‐bleach (c‐b) cycles exhibit reflectance contrast changes, , and charging times, τ, suitable for electrooptic display devices, e.g., for a film 320 nm thick, at and . Long term corrosion stability is obtainable in mildly acidic sulfate electrolytes, e.g., at pH 3.5. Sulfate electrolytes are also apparently unique in preventing degradation of c‐b response times owing to changes in film structure. East write‐erase times are made possible by the highly porous and hydrated nature of the oxide film and the ready availability of the protons required for bleaching from an 'internal' source—free molecules in the electrolyte contained within the film pores and/or bound or OH groups on the oxide surface. The kinetics and mechanism of the electrochromic reaction in anodic iridium oxide films are discussed with particular reference to the requirement for preserving electroneutrality within the bulk oxide. Recent claims that this redox reaction can occur without exchange of protons with the electrolyte are shown not to be substantiated. Attractive features of the electrochromic iridium oxide system for display devices include: (i) broad spectral absorption; (ii) good contrast ratio; (iii) fast response; (iv) good corrosion stability; (v) good open‐circuit memory in the presence of water and dissolved ; (vi) suitable threshold and switching voltage levels; and (vii) the ability to grow and reform the oxide layer in situ in the electrooptic display cell. The charge (~20 mC cm−2) and energy (~30 mJ cm−2) required for coloration and bleaching are similar to those required for other electrochromic oxide systems, e.g., the tungsten bronzes.

Model for the bleaching of WO3 electrochromic films by an electric field

Abstract: Measurements have been made of the current flow in amorphous WO3 films containing electrons and mobile cations. In a configuration in which electrons are extracted at one contact and cations at the other, the current decays as t−3/4 over many decades of time. By using space‐charge current flow ideas, we develop a theory that gives the correct time dependence and magnitude of the current for this double‐extraction phenomenon.

Ultra-large optical modulation of electrochromic porous WO3 film and the local monitoring of redox activity

Abstract: Porous WO3 films with ultra-high transmittance modulation were successfully fabricated on different substrates by a novel, facile and economical pulsed electrochemical deposited method with 1.1 s interval time between each pulse. The near ideal optical modulation (97.7% at 633 nm), fast switching speed (6 and 2.7 s), high coloration efficiency (118.3 cm2 C−1), and excellent cycling stability are achieved by the porous WO3 on ITO-coated glass. The outstanding electrochromic performances of the porous WO3 film were mainly attributed to the porous structure, which facilitates the charge-transfer, promotes the electrolyte infiltration and alleviates the expansion of the WO3 during H+ insertion compared to that of the compact structure. In addition, the relationships between the structural and electrochemical activity of the electrochromic WO3 films were further explored by the scanning electrochemical microscopy. These results testify that the porous structure can promote the infiltration of electrolyte and reduce the diffusion path, which consequently enhance the electrochemical activity.

Multiply Colored Electrochromic Carbazole-Based Polymers

Abstract: We report the synthesis and electrochemical polymerization of a series of bisheterocycle-N-substituted carbazoles. These monomers exhibit low peak oxidation potentials (Ep,m) which range from 0.15 to 0.46 V vs Ag/Ag+, indicating facile polymerization. Repeated scan electrochemical polymerization for these monomers proceeds rapidly, relative to carbazole, to form stable electroactive films. Cyclic voltammetry of the polymers indicates that the films are well adhered to the electrode surface and that each of the polymers possess two distinct redox waves. At applied potentials greater than 1.15 V, a third irreversible oxidative process is observed, presumedly due to cross-linking. Optoelectrochemical analysis indicates that these polymers have an electronic bandgap (measured as the onset of the π-to-π* transition) between 2.4 and 2.5 eV. Three distinct colors are achievable by varying the redox state of the polymers suggesting potential use for multiply colored electrochromic displays. For the series of bis(...