Steering Cascade Kinetics via In-Situ Electrochemical Reconstruction of Oxygen Vacancy-Rich Heterojunctions for Industrial-Current Nitrate-to-Ammonia Electrosynthesis

Abstract

The electrochemical nitrate reduction reaction (NO3RR) provides a sustainable route for ammonia (NH3) synthesis and nitrate wastewater remediation but is limited by sluggish proton-coupled multielectron kinetics and competing side reactions. Herein, an oxygen-vacancy-rich OV-Cu2O-Co(OH)2 heterostructure is rationally constructed via controlled electrodeposition and in situ electrochemical reconstruction, generating a robust OV-enriched interface stable at current densities up to -1 A cm-2. The heterostructure enables an efficient cascade NO3RR pathway, in which Cu2O catalyzes NO3⁻ to NO2⁻ conversion, while OV-rich Co(OH)2 accelerates NO2⁻ hydrogenation to NH3, suppressing NO2⁻ accumulation. Oxygen vacancies further enhance water dissociation, ensuring continuous proton supply. In situ spectroscopy and density functional theory reveal that oxygen vacancies optimize *NO adsorption and lower the energy barrier of the rate-determining *NO → *NOH step. Consequently, the catalyst delivers a NH3 yield rate of 4.73 mmol h-1 cm-2 with 97.5% Faradaic efficiency at -0.8 V vs. RHE and maintains 95.1% efficiency over 50 cycles at -1 A cm-2.