Utilizing the Wadsley-Roth structures in TiNb₂O₇@C microspheres for efficient electrochemical nitrogen reduction at ambient conditions

The electrochemical nitrogen reduction reaction (NRR) is an attractive approach for sustainable ammonia production, which is anticipated as a potential carbon–neutral hydrogen carrier. However, compared to the competing HER, the NRR suffers from a major drawback of low selectivity and conversion efficiency due to the high negative potential driving the NRR. Therefore, developing optimal electrocatalysts that inhibit the HER and promote the NRR is crucial for electrochemical ammonia synthesis. In this study, we demonstrated that TiNb₂O₇@C (TNO@C) microspheres with Wadsley-Roth crystal structure as efficient NRR electrocatalysts. The prepared TNO@C microspheres were calcined at controlled temperatures, and their electrochemical performances were investigated in different electrolytes. The cationic size effects and the pH of the electrolytes were analyzed to influence the NRR activity actively. The prepared TNO@C900 electrocatalyst exhibits high faradaic efficiency (13.11%) and ammonia yield (0.62 µmol h⁻¹ cm⁻²). The prepared TNO@C900 microspheres with Lewis acid sites of the Nb cations and the oxygen vacancy (V_o) coupled Ti cations can effectively improve the NRR performances of TNO@C electrocatalysts. Further, the in situ and theoretical analysis reveals the associative NRR pathway, and the purity and source of produced ammonia were carefully verified. This work elucidates that a controlled surface and morphology engineering strategy with appropriate NRR active elements can significantly increase the faradaic efficiency and ammonia yield. Graphical abstract: (Figure presented.)