Mimicking π Backdonation in Ce-MOFs for Solar-Driven Ammonia Synthesis

π Backdonation is the core process to break through the kinetically complex and energetic hurdle for catalyzing effectively the NH₃ synthesis but only occurs on certain transition metals with empty and filled d orbitals. Herein, mimicking π backdonation enables MOF-76(Ce) materials to convert N₂/NH₃ effectively. Note that, by virtue of the intrinsic mechanism of ligand-to-metal charge transfer, metal cerium species in MOF-76(Ce) serve as an electron sink for accumulating the photogenerated electrons. Taken together, experimental and theoretical analyses reveal that such metal cerium species with coordination unsaturated state (Ce-CUS) on a MOF-76(Ce) nanorod surface can also provide unoccupied and occupied 4f orbitals to accept from and then donate electrons back to nitrogen molecules. Remarkably, it shows outstanding photocatalytic nitrogen reduction performance with high average NH₃ yield (34 μmol g^-1 h^-1) under ambient conditions. This work provides fresh insights into rational designing and engineering highly active catalysts with rare earth elements.