Interfacial Electronic and Microstructural Modulation Synergistically Inducing Efficient and Stable Hydrogen Evolution Reaction Catalysis in S‐FeS 2 /Fe 3 O 4 ‐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‐ FeS 2 /Fe 3 O 4 ‐CNT microspheres are constructed to integrate FeS 2 /Fe 3 O 4 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 FeS 2 /Fe 3 O 4 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‐FeS 2 /Fe 3 O 4 ‐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‐FeS 2 /Fe 3 O 4 ‐CNTs||RuO 2 electrolyzer delivers lower cell voltages than the Pt/C||RuO 2 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.