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 O_V-Cu₂O–Co(OH)₂ heterostructure is rationally constructed via controlled electrodeposition and in situ electrochemical reconstruction, generating a robust O_V-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 O_V-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.