Mo‐Induced Crystalline/Amorphous Ru‐Ni ₃ Fe/NiMoFeO _x Heterointerface for Efficient and Robust Overall Water Splitting at High Current Density

ABSTRACT Developing efficient and stable bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) remains a challenge. Here, we report a Ru‐Ni 3 Fe/NiMoFeO x heterostructure electrocatalyst composed of Ru‐doped Ni 3 Fe alloy nanoparticles and amorphous NiMoFeO x nanosheets for efficient alkaline overall water splitting. Mo plays important dual roles in the synthesis process: first, it promotes the formation of amorphous components to construct an amorphous/crystalline heterostructure and accelerating the reconstruction of OER‐active NiOOH species in electrocatalysis. Second, it can suppress alloy nanoparticles growth to achieve a small average size of about 7.5 nm, thereby forming the abundant heterointerfaces and providing more active sites. Consequently, the prepared Ru‐Ni 3 Fe/NiMoFeO x catalyst exhibits excellent electrochemical performance, requiring the low overpotentials of 117 and 275 mV at a high current density of 1000 mA cm −2 for HER and OER, respectively. A water splitting electrolyzer assembled with this catalyst as the cathode and anode only needs 1.91 V at 1000 mA cm −2 and can run stably for 2000 h. This work demonstrates that leveraging the dual role of Mo to regulate phase evolution and suppress nanoparticle growth is an effective strategy for constructing active crystalline/amorphous heterointerfaces, guiding the design of bifunctional electrocatalysts for high‐current‐density alkaline water electrolysis.