Bismuth-Doped Heterostructured Oxide-Derived Copper for Efficient Nitrate Reduction to Ammonia

Abstract

Electrochemical nitrate reduction (NO3RR) has emerged as a sustainable route for green ammonia (NH3) synthesis, simultaneously enabling the remediation of nitrate-contaminated wastewater and supporting carbon-neutral nitrogen cycling. However, achieving a delicate balance between suppressing the competitive hydrogen evolution reaction (HER) and ensuring sufficient protonation for NH3 formation remains a major challenge. Here, we present a bismuth-doped heterostructured oxide-derived copper (Bi/HOD-Cu) electrode that addresses this challenge through catalytic cooperation. The Cu2O/Cu heterostructure of HOD-Cu accelerates the initial electron transfer and promotes *NO3 to *NO2 conversion, while controlled Bi incorporation effectively suppresses HER and stabilizes the key *NO2 intermediate, confirmed by in situ Raman spectroscopy. This cooperative mechanism drives highly selective protonation toward NH3. Accordingly, the optimized Bi0.7/HOD-Cu electrode achieves an NH3 Faradaic efficiency (FE) of 94.3% with a partial current density of –278.3 mA·cm–2 at –1.4 V vs RHE. When integrated into a zero-gap membrane electrode assembly (MEA) electrolyzer, the electrode maintains an NH3 FE of 80.1% at a practical current density of 400 mA·cm–2 over 50 h of continuous operation, demonstrating its scalability toward sustainable ammonia production.