6 g of the ATO powder was dispersed in 1200 g water, followed by adding 11.5 g IrCl₄. Subsequently, the aqueous medium was heated to 80° C. and KOH was added until pH=7. From time to time, further KOH was added so as to keep the pH at about 7.

After stirring for about 1 hour, the aqueous medium was cooled to room temperature, the ATO powder was separated from the aqueous medium by filtration, washed with water, and calcined in air at 600° C. for about 60 minutes.

The final catalyst composition had an electrical conductivity of 18 S/cm, a BET surface area of 52 m²/g, and an iridium content of 38 wt %. All iridium was in oxidation state +IV. The tin oxide particles (representing the core) are at least partially coated by an iridium oxide layer (representing the shell).

Testing the Electrochemical Performance and Corrosion Stability

The catalyst compositions of Inventive Examples 1 to 5 were tested for their electrochemical performance and corrosion stability under highly corrosive conditions.

For comparative purposes, the following samples were tested as well:

Non-supported metallic iridium black powder, BET surface area: 60 m²/g.

Non-supported iridium(IV) oxide powder; BET surface area: 25 m2/g.