High-efficiency electrocatalysts have been widely applied in various fields, especially in the counter electrode (CE) of dye-sensitized solar cells (DSSCs). Different from the usual methods for developing high-performance CE materials through searching new materials and designing new nanostructure, we utilized a rapid surface sulfurization treatment to activate the well-known Co3O4 material by increasing the adsorption energy of iodine (I) atom in the electrolyte of DSSCs. The density functional theory (DFT) calculation indicated the adsorption energy of Co3O4 (EadI 0.347 eV) toward I atom was dramatically increased to 0.835 eV through just transforming Co3O4 at surface into Co3S4. After a short activation time of 30 s, Co3O4 CEs showed a superior catalytic performance toward iodide electrolyte comparable with traditional Pt CE, generating a power conversion efficiency of 8.6% in DSSCs. This method of adjusting adsorption energy via surface sulfurization is applicable in the activation of other metal oxid...