Developing highly active and durable electrocatalysts for the oxygen evolution reaction (OER) is of pivotal importance for the widespread deployment of water splitting cells. Co3O4-based electrocatalysts have been of particular interests due to high OER activity. In the present work, a series of transitionmetal-doped Co3O4 electrocatalysts have been prepared for systematic investigation of impact of dopants on the activity and durability. For the OER, the addition of dopant improves activity of catalysts, with Sn-doped Co3O4 (Sn-Co3O4) showing the best electrocatalytic activity followed by Ni-Co3O4, Fe-Co3O4, and Co3O4 (in the order of activity). Highly active Sn-Co3O4 and Ni-Co3O4 reach 10 mA cm(-2) at a low overpotential of 0.354 V and 0.360 V, respectively, which is close to Ir/C (0.373 V). The addition of transition metal invokes change of crystallite size of Co3O4 and the overpotential of each catalyst shows a linear relationship with the crystallite size and geometric surface area. The Ni-Co3O4 catalyst exhibits significantly enhanced durability compared to the pure Co3O4 catalyst. Raman spectra and transmission electron microscopy after cycling tests reveal that the incorporation of multivalent Ni cations on the octahedral and tetrahedral sites of spinel structure Co3O4 effectively mitigates surface amorphization of catalysts, thereby enhancing the durability. (C) 2016 The Electrochemical Society. All rights reserved.