Interfacial Electronic and Microstructural Modulation Synergistically Inducing Efficient and Stable Hydrogen Evolution Reaction Catalysis in S-FeS₂/Fe₃O₄-CNT Microspheres Across a Broad pH Spectrum

Developing efficient and durable Fe-based electrocatalysts for the hydrogen evolution reaction (HER) across a broad pH range remains challenging because of sluggish interfacial charge transfer, inefficient water activation, limited active-site accessibility, and insufficient structural stability. Herein, hierarchical porous S- FeS₂/Fe₃O₄-CNT microspheres are constructed to integrate FeS₂/Fe₃O₄ heterointerfaces, interconnected carbon nanotube networks, and penetrative mass-transport channels. Spectroscopic characterization, operando Raman analysis, and density functional theory calculations reveal that interfacial electronic redistribution at the FeS₂/Fe₃O₄ heterojunction facilitates water adsorption and dissociation while optimizing H^* adsorption energetics. The CNT framework provides continuous electron-transport pathways, whereas three-dimensional tomography and permeability simulations demonstrate that accessible heterointerfaces are distributed throughout the microspheres and connected pores promote electrolyte transport to the internal active sites. Consequently, S-FeS₂/Fe₃O₄-CNTs exhibit competitive HER activity across acidic, alkaline, and neutral seawater, requiring overpotentials of 273.52, 82.97, and 248.04 mV, respectively, to reach 10 mA cm⁻², together with long-term operational stability. Moreover, the S-FeS₂/Fe₃O₄-CNTs||RuO₂ electrolyzer delivers lower cell voltages than the Pt/C||RuO₂ benchmark under identical seawater electrolysis conditions. This work establishes a multiscale design strategy for earth-abundant electrocatalysts by coupling interfacial electronic regulation, conductive-network construction, active-site accessibility, and mass-transport engineering.