Electrochemical quartz crystal microbalance study and electrochromic behavior of a novel ruthenium purple film

Abstract

Abstract Thin films of ferric-ruthenocyanide, also known as ruthernium purple (RP) can be readily prepared by repetitive potential cycling onto a number of different conducting materials such as glassy carbon, gold, platinum and indium-tin-oxide (ITO). This procedure is successfully accomplished provided that the supporting electrolyte, containing 0.5 mM FeCl 3 + 0.5 mM K 4 Ru(CN) 6 , is moderately concentrated in potassium electrolytes, i.e. 40 mM KCl + HCl at pH 2. Electrode stability of RP films was found greatly enhanced by cycling the inorganic film in millimolar solutions of RuCl 3 . 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, respecsbvely. Its voltammetric profile remains unchanged after ca. 1500 oxidation-reduction cycles at 50 mV/s (14 h of potential cycling). The stabilisation process in RuCl 3 solutions of as-grown RP films on platinum coated quartz crystals was followed concurrently by electrochemical quartz crystal microbalance (ECQM). The absorption spectra of the film on a ITO-covered glass electrode polarised to +0.50 V exhibits an absorption band at about 545 nm. The electrochemic activity and ease of preparation of Ru(III)