The invention relates to an electrode formulation comprising a catalytic layer containing tin, ruthenium, iridium, palladium and niobium oxides applied to a titanium or other valve metal substrate. A protective layer based on titanium oxide modified with oxides of other elements such as tantalum, niobium or bismuth may be interposed between the substrate and the catalytic layer. The thus obtained electrode is suitable for use as an anode in electrolysis cells for chlorine production.