Heterointerface Spin‐Regulated Dynamic Mo Ionic Bridge in 2D Polyoxometalates for Boosted Water Splitting and Seawater Uranium Extraction

ABSTRACT The catalytic utility of Keggin‑type phosphomolybdic acid hydrate (H 3 PMo 12 O 40 , PM) is severely limited by its inherent single‑cluster structure with aggregation tendency and low electronic conductivity. Herein, we fabricated a highly ordered 2D TDA‐PM structure via molecular‐level regulation. This architecture integrates electronegativity with extended electronic delocalization, conferring enhanced electron sponge behavior for efficient electron capture and release. Building on this, a TDA‑PM/IO‐V O heterojunction photoanode was constructed via electrostatic self‑assembly of TDA‑PM with positively charged, oxygen‑vacancy‑rich In 2 O 3 (IO‐V O ). The resulting photoanode achieves overall water‑splitting rates of 99.3 and 58.8 µmol cm −2 h −1 for H 2 and O 2 evolution, corresponding to 21.5‐ and 2.3‐times improvements over pure TDA‐PM and IO‐V O , respectively. Combined experimental and theoretical analyses confirm that heterointerface engineering effectively modulates the spin polarization of TDA‑PM, which dynamically maintains the variable‐valence Mo 5+ /Mo 6+ ionic bridge via reversible oxidation state transitions. This effect, in conjunction with TDA‑PM's electron sponge behavior, significantly boosts charge transport in the photoelectrode and downshifts its d‐band center, thereby strengthening water adsorption and reducing the energy barrier for the rate‐determining step of the oxygen evolution reaction (OER). Finally, upon integration with a continuous‐flow reactor, the system attains a U(VI) extraction capacity of 3746.7 mg g −1 day −1 in seawater.