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 PtO_0.12±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.