Built‐In Electric Field in Freestanding Hydroxide/Sulfide Heterostructures for Industrially Relevant Oxygen Evolution

Abstract Alkaline water electrolysis (AWE), as a premier technology to massively produce green hydrogen, hinges on outstanding oxygen evolution reaction (OER) electrodes with high activity and robust stability under high current densities. However, it is often challenged by issues such as catalytic layer shedding, ion dissolution, and inefficient bubble desorption. Herein, a scalable corrosion‐electrodeposition method is presented to synthesize nickel–iron layered double hydroxide (NiFe‐LDH)/Ni 3 S 2 heterostructures on nickel mesh, tailored to meet the stringent requirements of industrial AWE. The study underscores the critical role of the built‐in electric field (BEF) in optimizing electronic properties, curtailing Fe leaching, and enhancing mass transfer. The resultant NiFe‐LDH/Ni 3 S 2 heterostructure manifests remarkable OER performance, with ultra‐low overpotentials of 202 mV at 10 mA cm −2 and 290 mV at 800 mA cm −2 in 1.0  m  KOH at 25 °C, alongside superior steady‐state stability and resistance to reverse current under fluctuating conditions. Furthermore, the performance is further validated in an alkaline electrolyzer, achieving a large current density of 800 mA cm −2 at a cell voltage of 1.908 V, while maintaining excellent stability. This work offers a blueprint for the design of efficient OER electrodes for industrially relevant AWE applications.