Deciphering the In Situ Reconstruction of Metal Phosphide/Nitride Dual Heterostructures for Robust Alkaline Hydrogen Evolution Above 3 A cm⁻²

Abstract Hydrogen evolution reaction (HER) in neutral or alkaline electrolytes is appealing for sustainable hydrogen production driven by water splitting, but generally suffers from unsatisfied catalytic activities at high current densities owing to extra kinetic energy barriers required to generate protons through water dissociation. In response, here, a competitive Ni₃N/Co₃N/CoP electrocatalyst with multifunctional interfacial sites and multilevel interfaces, in which Ni₃N/CoP performs as active sites to boost initial water dissociation and Co₃N/CoP accelerates subsequent hydrogen adsorption process as confirmed by density functional theory calculations and in situ X‐ray photoelectron spectroscopy analysis, is reported. This hybrid catalyst possesses extraordinary HER activity in base, featured by extremely low overpotentials of 115 and 142 mV to afford 500 and 1000 mA cm⁻², respectively, outperforming most ever‐reported metal phosphides‐based catalysts. This catalyst presents an ultrahigh current density of 3545 mA cm⁻² by a factor of 4.96 relative to noble Pt/C catalysts (715 mA cm⁻²) at 0.2 V. Assembled with Fe(PO₃)₂/Ni₂P anode, industrial‐level current densities of 500/1000 mA cm⁻² at ultralow cell voltages of 1.62/1.66 V for overall water electrolysis with outstanding long‐term stability are actualized. More interestingly, this hybrid catalyst also performs well in acidic, neutral freshwater, and seawater requiring relatively low overpotentials of 140, 290, and 331 mV to reach 500 mA cm⁻². Particularly, this catalyst can withstand electrochemical corrosion without obvious activity decay at the industrial‐level current densities for over 100 h in base. This work provides a cornerstone for the construction of advanced catalysts operated in different pH environments.