Triggering the lattice oxygen oxidation mechanism is crucial for enhancing oxygen evolution reaction (OER) performance; yet, effectively boosting lattice oxygen participation and stability remains a challenge. Herein, iron-doped cobalt sulfides (Fe–CoSx) on carbon cloth are successfully synthesized via a one-step electrodeposition method. The optimal CoFe0.16Sx electrocatalyst exhibits remarkable OER performance, requiring overpotentials of only 220 and 300 mV to achieve 100 and 500 mA cm−2 in alkaline seawater, respectively, along with outstanding stability for over 125 h. Comprehensive characterization reveals that Fe doping plays multiple critical roles: (i) it significantly strengthens the adsorption of hydroxide ions (OH−), accelerates the in situ reconstruction of the catalyst surface and facilitates the deep oxidation of CoOOH to CoO2, thereby promoting a more efficient LOM pathway; and (ii) it stabilizes sulfate ions on the reconstructed surface, forming a protective layer that electrostatically repels chloride ions. These endow the catalyst with superior corrosion resistance and stable OER activity in chloride-containing alkaline electrolytes. This work provides an effective multifunctional doping strategy and mechanistic insights for the design of high-performance, stable OER electrocatalysts.