Abstract: Direct electrolysis of seawater is a greener and more sustainable route to a source of hydrogen energy production. However, seawater electrolysis needs to face the toxicity of harmful ions in seawater, especially the interference of chlorine evolution reaction (CER) with anode oxygen evolution reaction (OER) triggered by high concentration of Cl⁻ in seawater. Therefore the adoption of effective Cl⁻ shielding strategies to improve the OER performance and long-term electrolysis lifetime of the catalysts is crucial for the wide-scale development of seawater hydrogen production. In this work, NiFe-S/NF electrocatalyst for seawater electrolysis was successfully prepared on nickel foam (NF) substrates via one-step hydrothermal vulcanisation. Notably, NiFe-S/NF easily reaches 100 mA/cm² in alkaline freshwater (1 mol/L KOH + ultrapure water) and seawater (1 mol/L KOH + Seawater) requiring 237 and 248 mV, respectively, and has a seawater electrolysis endurance of more than 100 h (100 mA/cm²). This is attributed to the oxidation of sulphur in sulphide to sulphur-oxygen anions during the OER process, which are adsorbed on the surface of the electrode, accelerating the OER process of the electrocatalyst on the one hand, and forming a Cl⁻ shielding layer through electrostatic repulsion on the other hand, thus enhancing the performance and lifetime of the catalyst. This study provides a highly feasible strategy for the efficient and economic development of seawater hydrogen production.