In Situ Construction of Co‐Modified Ni/Ni ₃ P@C Heterostructures via MOF‐Derived Internal Phosphorus Source Engineering for Efficient and Stable Overall Water Splitting

The commercialization of green hydrogen via alkaline water splitting is limited by the lack of efficient bifunctional electrocatalysts. Heterostructure engineering and heteroatom modification are well‐established strategies to modulate electronic structures and boost catalytic activity, yet precise control over heterointerface formation and active‐site dispersion remains challenging. Herein, we report an internal phosphorus source engineering strategy to construct a carbon‐coated Co‐modified Ni/Ni 3 P heterostructure (Co‐Ni/Ni 3 P@C) as a robust bifunctional catalyst. In this approach, Na 2 HPO 4 decomposes and diffuses into the channels of NiCo‐MOF‐74, selectively coordinating with unsaturated metal sites to serve as a uniformly distributed internal phosphorus source. Subsequent H 2 /Ar annealing enables in situ generation of the Co‐Ni/Ni 3 P@C heterostructures with well‐dispersed active sites encapsulated in a carbon matrix. Comprehensive characterizations confirm that the synergy between heterointerface engineering and Co modification collectively optimizes the electronic structure, accelerates charge transfer, and increases the exposure of electrochemically active sites. Consequently, the catalyst exhibits low overpotential of 226 mV for HER and 280 mV for OER at 10 mA cm −2 . When integrated into an alkaline electrolyzer, it requires only 1.72 V to deliver the same current density and can be effectively driven by a commercial 1.5 V solar cell, highlighting its potential for integration with renewable energy systems.