Abstract

Selective electrosynthesis of urea via C–N coupling is limited by inefficient intermediate activation and competing hydrogen evolution reactions. Herein, we report a CO₂ laser-induced non-equilibrium thermal engineering approach for constructing electronically polarized Bi–O‒Sn interfacial sites through near-surface, atomic-scale Bi substitution at Sn lattice sites in SnO₂ nanosheets (Bi_AS–SnO₂). Structural analyses confirm that Bi atoms occupy near-surface Sn lattice sites while preserving the rutile SnO₂ framework and forming mixed-valence Bi–O–Sn coordination environments. Near-surface atomic-scale Bi substitution induces valence-electron redistribution among Bi, O, and Sn at the Bi–O–Sn interfacial sites and lowers the work function of the Bi_AS–SnO₂ surface from 4.22 eV for pristine SnO₂ to 2.20 eV, accelerating interfacial electron transfer and optimizing hydrogen adsorption–desorption kinetics to balance proton availability while suppressing hydrogen evolution reaction. Bi_AS-SnO₂ enables selective urea electrosynthesis through the co-reduction of formate (HCOO⁻) and nitrate (NO₃⁻) via a dual-reaction pathway, where HCOO⁻ undergoes reduction through an inner-sphere adsorption mechanism, whereas NO₃⁻ activation proceeds via outer-sphere electron transfer. This synergistic process synchronizes the generation of *CO and *NH₂ intermediates. In situ spectroelectrochemistry measurements and density functional theory calculations reveal that Bi substitution, coupled with oxygen-vacancy formation, creates defect states near the Fermi level and electronically polarized Sn_6c sites that efficiently generate *CO and *NH₂ intermediates. Furthermore, adjacent Sn_6c/Sn_5c sites promote associative *CO‒*NH₂ coupling with a low calculated energy barrier of 0.23 eV, resulting in high urea selectivity with a urea Faradaic efficiency of 86.9%. This study establishes an oxyanion-derived HCOO⁻–NO₃⁻ coupling strategy for urea electrosynthesis and provides a framework for designing electronically polarized interfaces that promote selective C–N coupling reactions.