Electrochromism of mixed polyacid films and its application for a smart window

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(1).Development and Evaluation of New Electrochromic filmsPeroxo-polymolybdotungstates are formed by the direct reaction of a mixture of metallic Mo and W (for example, 5 : 5 mixture) with hydrogen peroxide solution. A homogeneous and amorphous thin film (0.4 mum, typically) is fabricated on an ITO glass substrate by spin-coating using such a solution. After heat-treatment at 120 *, it exhibits electrochromism excellent in both reversibilty and response time in an organic Li-electrolyte.The film colored at -1V (vs. Ag/AgCl) shows rather flat absorption spectrum. Its color is dark grayish blue and the DELTAOD between -1V and +0.5V reaches 0.7 at 670nm (lambda_<max>). Kinetic aspect of such electrochroic films will also be discussed.(2).Coloration of electrochromic film in contact with polymer electrolyteElectrochromic thin film of amorphous WO_3・nH_2O was fabricated by spin-coating a peroxo-polytungstate solytion. Coloration and bleaching kinetics of the film incontact with a solid polymer electrolyte were investigated by a chrono-amperometric method using a cell, Li/polymer/WO_3・nH_2O, ITO.The transition currents were analyzed on the basis of a newly proposed theory to be able to describe the diffusion-controlled current generated by a voltage step in such a cell without a reference electrode. It was found that both kinetics were controlled by the diffusion process and the chemical diffusion coefficients of Li were, in common, about 5 x 10^<-12> cm^2/s.(3).Fabrication and evaluation of an electrochromic window prototypeA new thin film proton conductor based on tantalum oxide was developed from peroxo-tantalic acid. A prototype of electrochromic window in the tungsten oxide/Prussian blue system was fabricated using this conductor as an ion conducting layr. Successful and stable coloration-bleaching performance was demonstrated.