Mixed-valence {Mo₁₆} polyoxometalate enables redox-mediated active site regeneration for superior photocatalytic N₂...

Photocatalytic nitrogen fixation is often hindered by the rapid recombination of photogenerated charge carriers and the difficulty in activating inert N₂ molecules. Herein, an efficient {Mo₁₆}/gC₃N₅COOH photocatalyst is constructed via electrostatic interaction between mixed-valence molybdenum polyoxometalate {Mo^V₁₂ Mo^VI₄} and carboxyl-functionalized gC₃N₅ (gC₃N₅COOH). Under simulated solar irradiation, the composite exhibits outstanding nitrogen fixation performance, achieving an average NH₃ generation rate of 763.2 μmol g^-1 h^-1 and an apparent quantum efficiency of 2.63% at 420 nm. This performance stems from the multi-electron transfer capability of {Mo₁₆}, which acts as an "electron sponge" to accept photogenerated electrons from gC₃N₅COOH. Electron-rich Mo^V sites activate N₂ via d-π* orbital overlap, weakening the NN bond. In the distal hydrogenation pathway, Mo^V directly donates electrons to the adsorbed N₂ molecule and is oxidized to Mo^VI. Subsequently, incoming photogenerated electrons rapidly reduce Mo^VI back to Mo^V, establishing a dynamic Mo^V/Mo^VI redox cycle. This cycle not only ensures a continuous multi-electron supply but also enables the self-regeneration of active sites. In situ FT-IR and density functional theory (DFT) calculations confirm a distal pathway with a reduced energy barrier for N₂ hydrogenation, highlighting the role of polyoxometalates in multi-electron photocatalysis and offering a design strategy for efficient nitrogen reduction catalysts.