ELECTROCHEMICAL QUARTZ-CRYSTAL MICROBALANCE STUDY AND ELECTROCHROMIC BEHAVIOR OF A NOVEL RUTHENIUM PURPLE FILM

Thin films of ferric-ruthenocyanide, also known as ruthenium purple (R P) can be readily prepared by repetitive potential cycling onto a numb er of different conducting materials such as glassy carbon, gold, plat inum and indium-tin-oxide (ITO). This procedure is successfully accomp lished provided that the supporting electrolyte, containing 0.5 mM FeC l3 + 0.5 mM K4Ru(CN)(6), is moderately concentrated in potassium elect rolytes, i.e. 40 mM KCl + HCl at pH 2. Electrode stability of RP films was found greatly enhanced by cycling the inorganic film in millimola r solutions of RuCl3. The resulting Ru(III)-RP film shows a single set of well-defined peaks with anodic and cathodic peak potentials at +0. 26 V, and +0.14 V vs. SCE, respectively. Its voltammetric profile rema ins unchanged after ca. 1500 oxidation-reduction cycles at 50 mV/s (14 h of potential cycling). The stabilisation process in RuCl3 solutions of as-grown RP films on platinum coated quartz crystals was followed concurrently by electrochemical quartz crystal microbalance (ECQM). Th e absorption spectra of the film on a ITO-covered glass electrode pola rised to +0.50 V exhibits an absorption band at about 545 nm. The elec trochromic activity and ease of preparation of Ru(III)-RP film electro des makes them good candidates for electrochromic appliances. (C) 1997 Elsevier Science S.A.