A rational design on oxygen evolution reaction (OER) catalysts is pivotal to the overall efficiency of water electrolysis. Numerous works have been devoted to understanding the cation leaching and surface reconstruction of some very active electrocatalysts, while few have been on intentionally promoting the surface in a controlled fashion. In this work, we report controllable anodic leaching of Cr in CoCr 2 O 4 by activating the pristine material at high potential, which enables the transformation of inactive spinel CoCr 2 O 4 into a highly active catalyst. The depletion of Cr and consumption of lattice oxygen facilitate surface defects and oxygen vacancies, exposing Co species to reconstruct into active Co oxyhydroxides differ from CoOOH. A novel mechanism with the evolution of tetrahedrally coordinated surface cation into octahedral configuration via non-concerted proton-electron transfer is proposed. This work shows the importance of controlled anodic potential in modifying the surface chemistry of electrocatalysts.