The cost-effective Fe-based nanomaterials for oxygen evolution reaction (OER) have attracted much attention as the candidates for noble metal free electrocatalysts. However, the facile and efficient synthesis method of Fe-based electrocatalysts has been still a big challenge limited by the low conductivity and intrinsic activity. In this work, a facile in-situ electrochemical activation pretreatment technique has been designed to modify the electronic structure and ion ratio (Fe3+/Fe-2(+)) for enhanced catalytic performance using Fe3O4 as precursor. The results for OER performances show that the electro-reduced Fe3O4 (R-Fe3O4) only needs a lower overpotential of 320 mV to reach the density of 10 mA cm(-2) in alkaline medium. It is noted that the present work provides a promising way for developing the OER performance for catalyst based on Fe3O4. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.