Bandgap-Broken Fe Spinel Electrocatalyst Enables Integrated Seawater Electrolysis

Despite considerable attention on spinel catalysts in electrocatalysis, achieving their distinct redox activity at the atomic scale for cathodic seawater splitting and anodic wastewater purification represents a huge challenge. In this work, we address this issue by constructing bandgap-broken Zn─O─Fe─O─Co heteroatomic bonds through the integration of reduced ZnFe₂O₄ and oxidized CoFe₂O₄ semiconductors within spinel-structured Zn_xCo_1-xFe₂O₄. The overlapping conduction and valence bands at Fe 3d orbitals promote electron redistribution at Fe centers, leading to electron depletion, exposure of empty d orbitals, and modulation of the d-band center. These electronic modifications enhance the adsorption kinetics of H₂O in seawater and S^2- species in wastewater through d-p orbital coupling, lowering the energy barriers for the Volmer step in hydrogen evolution reaction and the rate-limiting *S─*S₂ process in sulfur oxidation reaction. As a result, the rational design enables efficient bifunctional activity, achieving simultaneous seawater splitting and industrial pollutant degradation in a single electrolyzer at an ultralow cell voltage of 1.07 V (10 mA cm^-2), operable under solar energy. This study provides a fundamental design strategy for bifunctional catalysts toward integrated energy and environmental applications.