Oxygen evolution reactions (OER) have received recent attention because of their importance in electrochemical water splitting for sustainable energy sources. Here, the electrochemical OER activity on electrodeposited Pt sphere electrodes with porous structures was investigated. The dependence of the OER activity on the porosity of the Pt sphere electrodes was systemically examined by changing the charge during the electrodeposition of the Pt spheres. Significantly enhanced OER activities were observed on the porous Pt sphere electrodes compared to that on a flat Pt electrode, and the activity increased as the porosity of the Pt sphere increased. Pt spheres with rough nanoscale surface features exhibited greater OER activities than the smooth Pt sphere electrodes. The surfaces of the Pt sphere electrodes were modified with Ir by spontaneous replacement reactions, which resulted in an OER activity enhancement relative to the Pt sphere electrodes. The OER activity of Pt electrodes depending on the porosity and surface roughness demonstrated in this work gives insight into the fabrication of efficient OER electrocatalysts. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.