Phyto-Confined CeO_x with Synergistic Lattice Distortion and Oxygen Vacancies Drives Efficient Urea Electrosynthesis

Electrocatalytic urea synthesis from carbon dioxide and nitrates is hindered by sluggish multi-electron kinetics and unclear C-N coupling mechanism. Herein, lattice-distorted CeO_x nanoparticles are introduced with abundant oxygen vacancies (O_V), confined within a porous carbon framework (d-CeO_x/PC), fabricated via a phyto-hyperaccumulation confinement strategy. Precise structural modulation induces ultrasmall (≈2 nm), uniformly dispersed, contracted Ce─O bonds (≈2.29 Å) and creates a highly active environment for urea electrosynthesis. In situ ATR-FTIR spectroscopy identifies key intermediates, confirming C-N coupling pathway. Theoretical calculation reveals contracted bonds strengthen Ce 4f-O 2p orbital hybridization, restricting lattice oxygen (O_L) migration and slowing O_V diffusion/annihilation. Simultaneously, bond contraction induces localized electron redistribution around O_V. These O_V promote mixed Ce³⁺/Ce⁴⁺ valence, while the highly covalent, contracted Ce─O bonds stabilize Ce³⁺, forming localized "electron reservoirs" for flexible multi-step electron transfer. These synergistic effects enhance reactant (CO₂/NO₃ ^-) adsorption, stabilize key intermediates (*CO/*NO), and drastically lower the C-N coupling energy barrier (*NO+*CO→*OCNO, 0.18 eV), while suppressing competing hydrogenation pathways to byproducts. The porous carbon framework further improves durability (>100 h) and active site accessibility. This reduction in C-N barrier, identified as the key kinetic descriptor enabled by structural modulation, provides mechanistic insight for designing catalysts for sustainable urea production from waste.