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Platinum Metals Rev., 1991, 35, (2), 95

Binary Coatings for DSA®-type Electrodes

Prior to the development of dimensionally stable electrodes (DSA®) in the late 1960s, the production of chlorine and chlorate via the electrolysis of brine generally made use of graphite electrodes. Graphite electrodes required frequent maintenance, but DSA® electrodes preserve both their shape and their voltage characteristics, and facilitate significant electrical power savings. They consist of a thin active coating, capable of catalysing the desired electrochemical reaction and of passing the electric current between a base metal support and the interface of the electrode with the electrolyte. The coating consists of a noble metal oxide mixed with a conducting or non conducting stabilising oxide, while the support is generally a valve metal such as niobium, tantalum, titanium or zirconium.

Such anodes have been considered for a variety of electrochemical processes, and a communication from the Swiss Federal Institute of Technology, Lausanne, reports a systematic investigation of nine binary coatings made during the continuing search for a DSA®-type electrode suitable for oxygen evolution in concentrated. sulphuric acid solutions (Ch. Comninellis and G. P. Vercesi, J. Appl. Electrochem., 1991, 21, (4), 335-345).

On the basis of cost and performance titanium, which is used in most conventional DSA® applications, was selected as the base metal. The binary coatings consisted of a conducting oxide (RuO2, IrO2 or PtO0.12±0.05) and a non conducting stabilising component (TiO2, ZrO, or Ta2O5), and compositions ranging from 10 to 100 per cent of conducting oxide were tested. The results are discussed.

It was concluded that the titanium electrode coated with IrO2 and Ta2O5, 70 and 30 mol per cent, respectively, was the best tested. It also displayed the best catalyst dispersion and gave the longest service life.

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