P. Strasser et al., Chem. Sci., 2015, 6, pp. 3321-3328, describe the preparation of metallic iridium nanodendrites which are then deposited on an antimony-doped tin oxide (typically referred to as “ATO”) having a BET surface area of 263 m²/g. Before being tested as a catalyst in an oxygen evolution reaction, the surface of the metallic iridium nanodendrites is electrochemically oxidized in an acidic medium. However, by subjecting metallic iridium to an electrochemical oxidation under acidic conditions, some iridium may dissolve into the surrounding electrolyte. A similar approach is described by P. Strasser et al. in Angew. Chem., Int. Ed., 2015, 54, pp. 2975-2979. Oxide-supported IrNiOx core-shell particles are prepared from bimetallic IrNi_x precursor alloys using electrochemical Ni leaching and electrochemical oxidation of metallic iridium. As discussed by P. Strasser et al. in J. Am. Chem. Soc., 2016, 138 (38), pp 12552-12563, electrochemical oxidation of metallic iridium nanoparticles generates iridium oxide on the particle surface while the core still contains metallic iridium (i.e. iridium in oxidation state 0).