Synthesis and characterization of Iridium Oxide coatings stabilized with Tantalum Pentoxide

Dimensionally Stable Anodes (DSA®’s) are widely employed in the chlor-alkali technology and may be of interest also galvanic industry, as alternatives to lead anodes, owing to their good electrocatalytic properties and excellent wear-resistance under drastic electrolysis conditions ([1-3] and literature therein). The catalytically active components of the electrode films are VIII B group metals oxides (RuO2 and IrO2 in particular), which also afford good electric conductance to the electrode material. Other ceramic components, like TiO2, ZrO2, Ta2O5 and SnO2, (valve metal oxides) are added in order to increase the film wear resistance and achieve a better dispersion of the catalyst. RuO2-based electrodes are employed for chlorine evolution, while IrO2-based ones, because of their higher electrochemical stability under anodic oxygen evolution conditions, could find application as anodes in galvanic processes and electrowinning [5,6]. The papers appeared in the last 25 years showed that the physical and chemical properties of DSA® materials are strongly influenced by a number of parameters, like the nature of the precursor salts and their solution, the oxidation temperature, the pyrolysis time, the kind of metal support and the nature of the stabiliser [7-9]. The last one in particular plays a very important role in the DSAs designing, since contributes both to the device stability and on its catalytic properties [1]. The employment of glass-former oxides like Ta2O5, in particular, seems to improve the stability of the noble-metal oxide, possibly hindering its dissolution during the electrolysis [5]. The most widely used stabiliser in DSA®’s synthesis is TiO2 [1-3], which, however, seems to be more interesting in the preparation of electrodes for chlor-alkali cells. The performance of TiO2-stabilized mixed-oxide electrodes under oxygen evolution conditions, is in fact unsatisfactory. For this reason research has been extended to other stabilisers, like ZrO2 [7,8] and Ta2O5 [5,6]. Ta2O5 is of particular interest, due to its property of glass-former oxide [9]. The goal of this work is to investigate in detail the compositional and structural properties IrO2-Ta2O5/Ti anodes, with different nominal composition, by Secondary Ion Mass Spectrometry (SIMS). Cyclic voltammetry was employed to evaluate electrochemical surface area of the films and get some indication on their electrocatalytic activity, as a function of IrO2 content. Ref. 1. S. Trasatti and G. Lodi, in S. Trasatti (ed.), Electrodes of conductive metallic oxides, Elsevier Sci. Publ. Co., Amsterdam, (1980), pp.301-358. 2. S. Trasatti and G. Lodi, in S. Trasatti (ed.), Electrodes of conductive metallic oxiddes, Else vier Sci. Publ. Co., Amsterdam, (1981), pp.521-626. 3. D.M. Novak, B.V.Tilak, B.E.Conway, in B.E. Conway and J. O'M Bockris (eds.), Modern Aspects of Electrochemiistry, vol. 14, Plenum Press, New York, (1982), pp. 195-317. 4. Ch. Comninellis and G.P. Vercesi, J. Appl. Electrochem. 21 (1991) 136 5. J. Kolb, C.R. Franks, B.A. Schenker, U.S. Patent 3.793.164 6. J. Rolewicz, Ch. Comninellis, E. Plattner, J. Hinden, Electrochim. Acta 33 (1988) 573 [7-9] es. tre lavori presi dalla produzione in collaborazione con Veszprém 10. L.D. Burke and M. McCarthy, Electrochim. Acta 29 (1984) 211 11. A. Benedetti, P. Riello, G. Battaglin, A. De Battisti and A. Barbieri, J. Electroanal. Chem. 376 (1994) 195 12. K. Nassau, C.A. Wang and M. Grasso, J. Amer. Ceram. Soc. 66 (1979) 74