Synergy of Built‐In Electric Field and Surface Reconstruction of Co–NiS/Ni 3 S 2 Nanowires for Enhanced Bifunctional Activity and Anti‐Chlorine Corrosion in Seawater Electrolysis

ABSTRACT The development of efficient and stable bifunctional electrocatalysts is a key challenge for the industrialization of hydrogen production by water electrolysis. In this work, Co‐doped NiS/Ni 3 S 2 heterostructured nanowire arrays (Co–NiS/Ni 3 S 2 NA) were successfully constructed by precisely modulating the phase‐selective behavior of nickel sulfides through a cobalt doping strategy. The introduction of cobalt not only suppressed the formation of the sulfur‐rich phase NiS 2 but also promoted the generation of the Ni 3 S 2 phase to form a heterogeneous interface with high electrical conductivity. Benefiting from the electron redistribution at heterogeneous interfaces, optimization of d‐band center position, and improvement of electronic conductivity, the Co–NiS/Ni 3 S 2 NA catalyst exhibited excellent bifunctional activities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1 M KOH, with overpotentials at 10 mA cm −2 as low as 42 and 273 mV, respectively. In alkaline natural seawater (1 M KOH + seawater), the catalyst only required a low voltage of 1.764 V to achieve a high current density of 500 mA cm −2 for overall water splitting, with superb long‐term stability for 100 h. Ex situ Raman spectroscopy, differential electrochemical mass spectrometry, and theoretical calculation revealed that the OER process of Co–NiS/Ni 3 S 2 NA followed an adsorbate evolution mechanism, dynamic surface reconstruction forms active NiOOH species, and the formed sulfate creates electrostatic shields against chloride corrosion. This study provides valuable insights into the construction of sulfur‐deficient heterointerfaces and their electrocatalytic mechanisms, and the design of high‐efficiency and chloride‐resistant electrocatalysts for seawater electrolysis.