Interfacial Kinetic Matching in Amorphous Fe2O3/Crystalline Cu2O Enables Efficient Nitrate-To-Ammonia Electrosynthesis

Abstract

Electrochemical nitrate (NO3–) reduction to ammonia (NH3) is a promising route for simultaneous nitrate remediation and sustainable NH3 synthesis, yet remains challenged by sluggish multistep hydrogenation kinetics. Here, we report an amorphous Fe2O3/crystalline Cu2O catalyst (a-Fe2O3/c-Cu2O), in which ultrasmall Cu2O nanocrystallites are uniformly dispersed in an amorphous Fe2O3 matrix. The resulting a-Fe2O3/c-Cu2O interface induces strong electronic interaction and complementary catalytic functions. The pH-dependent potential analysis shows that a-Fe2O3/c-Cu2O maintains a highly alkaline interfacial microenvironment, while stepwise kinetic measurements reveal favorable kinetic matching between NO3– activation and subsequent NO2– hydrogenation. In situ spectroscopic studies reveal a tandem catalytic pathway in which NO3– is first activated on c-Cu2O to form NO2–, followed by transfer to adjacent a-Fe2O3 sites for hydrogenation to NH3. Consequently, a-Fe2O3/c-Cu2O achieves an NH3 Faradaic efficiency of 92.4% and an NH3 yield rate of 6.25 mmol h–1 mg–1, and sustains stable operation for 100 h in a membrane electrode assembly electrolyzer. This work offers a viable strategy for promoting nitrate-to-ammonia electrosynthesis through amorphous/crystalline interfacial engineering.