Hollow N-doped carbon nanofiber confined Ru/Ni3Fe@C core-shell heterostructures for boosted alkaline overall water splitting.

Nickel‑iron intermetallic Ni3Fe represents a low-cost oxygen evolution reaction (OER) electrocatalyst, yet sluggish hydrogen evolution reaction (HER) kinetics, severe particle aggregation and inferior alkaline stability greatly limit its bifunctional water-splitting application. Hierarchical hollow N-doped carbon nanofiber supported Ru/Ni3Fe@C core-shell heterostructures (Ru/Ni3Fe@C/CNF) are fabricated via coaxial electrospinning, high-temperature carbonization and liquid-phase Ru reduction. Hollow N-doped carbon nanofibers serve as conductive porous scaffolds, where graphitic carbon shells encapsulate Ni3Fe nanoparticles and evenly dispersed Ru nanoparticles form heterointerfaces for electronic regulation. Characterizations confirm carbon-triggered Ni3Fe lattice expansion, strong Ru-Ni/Fe charge transfer, and in-situ formation of NiOOH/FeOOH active sites under OER conditions. Electrochemical measurements in 1 M KOH deliver 61 mV HER and 240 mV OER overpotentials at 10 mA cm-2, outperforming Ni3Fe@C/CNF and commercial Pt/C/RuO2. Elevated double-layer capacitances (38.9 mF cm-2 for HER, 37.3 mF cm-2 for OER) and lowered charge transfer resistance demonstrate abundant exposed active sites. Benefiting from carbon confinement, 83% and 80% initial activity are maintained after 40 h HER and OER operation, respectively. The symmetric electrolyzer attains a low cell voltage of 1.64 V at 10 mA cm-2 with 92% activity retention over 100 h. Density Functional Theory (DFT) calculations confirm combined carbon encapsulation and Ru decoration upshift Ni3Fe d-band center, reduce water dissociation barrier to 0.46 eV and balance H⁎/OOH⁎ adsorption to accelerate catalytic kinetics. This work develops an integrated interface engineering strategy for high-efficiency durable non-noble bifunctional electrocatalysts.