A simplified method for WO3 electrodeposition

Cathodic electrodeposition is a promising route for electrochromic WO3 thin-film deposition. A new, simple, and fast method for preparing the deposition solution is described. Typically the solution consists in an equimolar mixture of 25 mM Na2WO4 and H2O2 acidified at pH 1.2 by perchloric acid addition. A film deposited at -0.24 V vs. a normal hydrogen electrode (NHE) grows at 1.2 mum h(-1). Most generally, the films are well-covering, highly disordered, and electrochromic. Above 100 nm, the porosity markedly increases with film thickness. The coloration efficiencies measured at a wavelength of 633 nm for H+ and Li+ intercalation range between 62 and 66 cm(2) C-1. A study by the electrochemical quartz crystal microbalance technique of the influence of the concentration ratio between hydrogen peroxide and the salt, the deposition solution aging, and the deposition potential has been conducted. We show in particular that the solutions present a good stability over several days and we discuss the influence of the hydrogen peroxide/tungstate ratio on the peroxy-tungstate precursor involved in the electrodeposition process. (C) 2002 The Electrochemical Society.