Light-Induced Electron-Rich Gold Directs Nitrate Reduction to Dinitrogen

Electrocatalytic nitrate reduction reaction (NO₃RR) provides a controllable route for nitrate conversion, while nitrate purification requires directing the reaction endpoint toward inert N₂ instead of soluble reactive nitrogen species. Here, we establish operating-state electron enrichment as a design principle for directing NO₃RR toward N₂ and construct a Cu-induced electronically reconfigured Au (ER-Au) interface that enters an electron-rich state under illumination. Electrochemical in situ interfacial characterization and theoretical calculations show that this electron-rich environment transforms *NO-related intermediates from isolated adsorption states into N-N coupling reactive configurations, selectively enabling the NO₃ ^- to N₂ branch. Consistent with this branch regulation mechanism, ER-Au selectively converts NO₃ ^- to N₂ with 90.84% Faradaic efficiency at pH = 1, as confirmed by product analysis and isotope-labeling experiments, and further maintains stable operation for 100 h under illuminated acidic NO₃RR conditions. The high N₂ Faradaic efficiency shows competitive performance among representative NO₃RR electrocatalysts reported in the literature, especially considering the challenge of directing nitrate reduction toward the inert N₂ endpoint. More broadly, these findings identify operating-state electron enrichment as a key mechanism and design principle for endpoint-selective NO₃RR.