The Built-in Electric Field Regulates the d-band Center of the FeCo2O4/ZnCdS Heterojunction to Enhance Photocatalytic Hydrogen Evolution.

Noble metal nanoparticle co-catalysts offer high photocatalytic activity but are costly and scarce, driving the search for efficient, economical alternatives. We constructed a FeCo₂O₄/ZnCdS composite catalyst using electrostatic self-assembly. Optimizing the FeCo₂O₄ loading to 10 wt% achieved a remarkable hydrogen production rate of 9080 μmol g^-1 h^-1-3.49 times higher than pristine ZnCdS and exceeding precious metal co-catalysts like Au. Kelvin probe force microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations reveal an S-scheme heterojunction forms between FeCo₂O₄ and ZnCdS. The resulting internal electric field efficiently drives directional charge migration and significantly suppresses electron-hole recombination. DFT further shows the interface electric field shifts the d-band center, optimizing reactant molecule adsorption. This avoids catalyst deactivation from strong adsorption while overcoming the energy barrier from weak adsorption, creating an ideal moderate-strength activated state. This work deepens understanding of S-scheme mechanisms and provides a new strategy for economical photocatalytic hydrogen production.