MECHANISM OF WO3 ELECTRODEPOSITION FROM PEROXY-TUNGSTATE SOLUTION

Electrodeposition of amorphous electrochromic tungsten trioxide (WO3) was studied, Good quality films were deposited cathodically onto tin-d oped indium oxide (ITO) from a water/isopropanol solution containing d issolved tungsten(VI) species. Three reducible species are present in this solution: unbound H2O2, polytungstate ions, and peroxytungstate i ons, The effects of the H2O2 content, which is related to the age of t he deposition solution, and of mass transport on the deposition curren t and deposition efficiency were determined and used to elucidate the mechanism of electrodeposition. Reduction of unbound H2O2 and polytung state did not result in film growth. This part of the current was unde r mixed diffusion-kinetic control. The remainder of the current was du e to reduction of peroxy-tungstate and was kinetically limited. This p rocess led to WO3 deposition. The current efficiency, defined as the n umber of electrons consumed by reduction of peroxy-tungstate per W ato m deposited, was about 1.6, in good agreement with the proposed deposi tion reaction.