In proton exchange membrane (PEM) water electrolysis, iridium oxide (IrO2) has often been utilized as a main catalyst for the oxygen evolution reaction (OER) as a rate-determining step. In general, the performance of PEM water electrolysis is dominantly affected by the specific surface area and the porous structure of the IrO2 catalyst. Thus, in this study, IrO2 and antimony-doped tin oxide (ATO) nanostructures with high specific surface areas were synthesized through the Adams fusion method. The as-prepared samples showed well-defined porous high-crystalline nanostructures. The ATO nanoparticles as a support were surrounded by IrO2 nanoparticles as a catalyst without serious agglomeration, indicating that the IrO2 catalyst was uniformly distributed on the ATO support. Compared to pure IrO2, the IrO2/ATO mixture electrodes showed superior OER properties because of their increased electrochemical active sites. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.