Electrochromism in electrodeposited nanocrystalline WO3 films I. Electrochemical and optical properties

New hexagonal tungsten trioxide films with perpendicularly oriented nanocry stallites were synthesized using the electrodeposition technique. Electroch emical and optical responses of these films to potential scanning and poten tial steps were investigated for films deposited under varying conditions a nd with different intercalating cations. We have found that both the electr ochemical kinetics and the optical switching are very fast, and in fact fas ter than for WO3 films deposited by any other technique. We attribute this rapid kinetics and fast optical switching ability of our WO3 films to their morphology and hexagonal structure. Especially striking feature of these f ilms is the preferential orientation of the {0001} atomic plane of each ind ividual nanocrystallite parallel to the film surface. Big one-dimensional h exagonal channels are thus preferentially formed normal to electrode surfac e and this arrangement is very favorable for the cation intercalation proce ss. Kinetic investigations indicate that the solid state diffusion is contr olling the intercalation process of H+ and D+ cations.