Deposition of small amounts of IrO2 clusters on the boron-doped diamond (BDD) surface (BDD-IrO2 electrode) dramatically enhances both the oxygen evolution reaction and the oxidation of organics in the potential region of water decomposition. The fact that BDD-IrO2 electrode behaves similarly to IrO2-DSA type electrodes suggests that the IrO2 clusters on the BDD surface act as redox catalysts in both oxygen evolution and organics oxidation.