Mechanism of the gasochromic coloration of porous WO3 films

Films of WO3 were coated with platinum and coloured by exposure to diluted hydrogen gas. Bleaching was achieved with diluted oxygen. Because of its si mple layer structure, this so-called gasochromic device is suitable for lam e area window applications. By variation of several parameters, such as fil m thickness and gas concentration, and by considering the bleaching in vacu um and argon, we found a model for the mechanism of the reaction. It is str ikingly different to the ideas of the double injection model, and there are indications that the gasochromic and electrochromic reactions are similar for porous films. According to our model, H-2 is dissociated on the platinu m, transferred into a pore or grain boundary of the WO3 and creates water a nd an oxygen vacancy. The O vacancy diffuses into the interior of the grain and the water slowly leaves the film. The bleaching in argon or vacuum is assumed to be the reverse reaction. The bleaching by oxygen is suggested to occur by by the dissociation of the O-2 on the platinum, transfer into a p ore and recombination with the oxygen vacancy. (C) 2000 Elsevier Science B. V. All rights reserved.