Lattice Alkali in Cu₃N Reprograms Interfacial Electronics for Selective Aqueous Nitrate-to-Ammonia

Electrochemical nitrate reduction to ammonia (NO₃RR → NH₃) suffers from poor selectivity and strong competition from hydrogen evolution. Here we show that materials-intrinsic electrostatic reprogramming of colloidal copper nitride (Cu₃N) nanocrystals provides a robust lever to bias NO₃RR. Two routes are established in a single electrolyte (0.50 M KNO₃ + 0.10 M KOH): (i) dilute Na incorporation that preserves the anti-ReO₃ (Pm-3m) lattice with small peak shifts, and (ii) Li treatment that amorphizes Cu₃N, yielding short-range–ordered Li–Cu–N. Across both families, cyclic voltammetry, LSV/Tafel analysis, and impedance spectroscopy reveal earlier cathodic onset (≈60–120 mV), reduced charge-transfer resistance (R_ct down to ~16 Ω from ~79 Ω for pristine), and favorable potential-of-zero-charge (PZC) shifts within the operating window. Chronoamperometry with indophenol quantification gives Faradaic efficiencies up to 74% and NH₃ production rates up to 8.8 × 10⁻³ mmol h⁻¹ mg⁻¹ (10% Li–Cu–N), with Tafel slopes of 120–167 mV dec⁻¹, consistent with a first electron-transfer step as rate determining. Electrolyte-cation spike and rinse–swap controls decouple double-layer effects from materials changes: gains on undoped Cu₃N vanish after rinsing, whereas Na-modified and Li-amorphous electrodes retain performance. The results delineate two complementary design paradigms lattice-level Na incorporation and controlled Li-induced amorphization that embed a beneficial interfacial field and accelerate NO₃RR without reactor or electrolyte redesign.