Two different forms of rutile-type iridium oxide catalysts were prepared: IrO2-coated titanium plate electrocatalysts prepared by a dip-coating method (IrO2/Ti) and iridium oxide nanoparticles (IrO2) prepared by a wet method, the Adams fusion method. The catalytic behavior of the oxygen reduction reaction (ORR) was evaluated by cyclic voltammetry in 0.5 M H2SO4 at 60 degrees C. Both catalysts were found to exhibit considerable activity for the ORR; however. the former oxide electrodes showed higher activity than the latter ones. All the IrO2/Ti catalyst electrodes heat-treated at a temperature between 400 degrees C and 550 degrees C showed ca. 0.84V (vs. RHE) of the onset potential for the ORR, E-ORR, where the reduction current of oxygen had begun to be observed during the cathodic potential sweep of the test electrodes. It has been confirmed clearly that IrO2, but neither metallic It nor the hydrated IrO2, behaves as an active catalyst for the ORR in an acidic solution. It was also demonstrated that the enlargement of the surface area of the IrO2/Ti with the help of lanthanum is effective for the enhancement of the catalytic activity in the reaction. (c) 2008 Elsevier Ltd. All rights reserved.