Creating Highly Active Iron Sites in Electrochemical N2 Reduction by Fabricating Strongly-Coupled Interfaces

Electrochemical N-c reduction has been regarded as one of the most promising approaches to producing ammonia under mild conditions, but there are remaining pressing challenges in improving the reaction rate and efficiency. Herein, an unconventional galvanic replacement reaction is reported to fabricate a unique hierarchical structure composed of Fe3O4-CeO2 bimetallic nanotubes covered by Fe2O3 ultrathin nanosheets. Control experiments reveal that CeO2 species play the essential role of stabilizer for Fe2+ cations. Compared with bare CeO2 and Fe2O3 nanotubes, the as-obtained Fe2O3/Fe3O4-CeO2 possesses a remarkably enhanced NH3 yield rate (30.9 mu g h(-1) mg(cat)(-1)) and Faradaic efficiency (26.3%). The enhancement can be attributed to the hierarchical feature that makes electrodes more easily to contact with electrolytes. More importantly, as verified by density functional theory calculations, the generation of Fe2O3-Fe3O4 heterogeneous junctions can efficiently optimize the reaction pathways, and the energy barrier of the potential determining step (the *N-2 hydrogenates into *N*NH) is significantly decreased.

Automated summary

This study reports an unconventional galvanic replacement reaction that fabricates a unique hierarchical structure of Fe3O4-CeO2 bimetallic nanotubes covered by Fe2O3 ultrathin nanosheets. The addition of CeO2 stabilizes Fe2+ cations, leading to remarkably enhanced NH3 yield rate and Faradaic efficiency. The hierarchical feature enhances electrode-electrolyte contact, while the generation of Fe2O3-Fe3O4 heterogeneous junctions optimizes the reaction pathways.