Self‐supported Fe‐Doped <scp> Ni ₃ S ₂ </scp> / <scp> NiP _<i>x</i> </scp> Heterojunction Electrocatalyst with Optimized Electronic Structure for Efficient Electrocatalytic Overall Water Splitting

Comprehensive Summary Designing bifunctional electrocatalysts with high activity, durability and low‐cost is a top priority to advance the hydrogen energy industry. Herein, self‐supported Fe‐doped Ni 3 S 2 /NiP x heterojunction electrocatalysts were synthesized via a simple hydrothermal and phosphorylated method. Benefiting from the unique nanowire morphology, abundant heterojunction interface and optimized electronic structure, it requires only low overpotentials of 263 and 173 mV at 100 mA·cm –2 current density to achieve oxygen evolution reaction and hydrogen evolution reaction in 1 M KOH solution, respectively, with excellent stability of 300 and 150 h. In addition, in situ Raman and in situ EIS demonstrated that Fe doping accelerated the surface remodeling of the catalysts, enhanced electron transport efficiency, thereby enhancing the activity and stability. Remarkably, Fe‐doped Ni 3 S 2 /NiP x electrocatalysts are assembled as both anode and cathode to achieve a current density of 100 mA·cm –2 in 1 M KOH and simulated seawater solution by requiring only low cell voltages of 1.517 and 1.561 V, and the loss is negligible in the 200 h endurance test. DEMS signals and density functional theory further demonstrate the intrinsic mechanism of the catalysts, doping engineering and heterogeneous interfaces can effectively reduce the energy barrier of rate‐determining step and accelerate catalytic overall water splitting.