Phosphate-Mediated Cl ^– Repulsion and B ₂ O ₃ –Assisted Hydroxylation Synergize Ionic Interface Stability in Seawater Splitting

Ionically bonded interfaces are crucial for achieving selective and stable direct seawater electrolysis, yet their vulnerability under corrosive and high-current conditions limits long-term performance. Here, we report a two-dimensional Fe-MOF@PW₈O₂₆.B₂O₃ heterostructured electrocatalyst, synthesized via a solid-liquid interfacial growth strategy, that integrates robust Fe-O-W and tunable Fe-P-W ionic bonds to strengthen interfacial electronic coupling, redox flexibility, and structural integrity. Subsurface B₂O₃ enhances surface hydroxylation via Lewis acid-base interactions, facilitating catalyst assembly and OH^- affinity, while phosphate polyanions at the interface act as electrostatic shields that repel Cl^- ions and modulate the redox environment of Fe active sites. This interfacial configuration enables chlorine-suppressive oxygen evolution with a Faradaic efficiency of 97.93%, achieving a current density of 1.75 A cm^-2 at 2.0 V and stable operation above 1.5 A cm^-2 for over 500 h in alkaline seawater, with an exceptionally low corrosion rate of 0.016 μm per year. NEXAFS and XPS analyses confirm the presence of dual ionic linkages, while DFT calculations reveal their cooperative role in stabilizing the electronic structure and interfacial charge distribution. Beyond hydrogen production, the spent electrolyte is repurposed for CO₂ mineralization, achieving 88.76% conversion to stable carbonates, with cytotoxicity assays confirming reduced environmental toxicity. Together, this study establishes a multifunctional ionically engineered platform for durable, chlorine-free seawater electrolysis and integrated carbon capture, advancing the prospects of circular hydrogen systems.