Fe³⁺/Fe²⁺-Tuned Iron Oxides for Enhanced Interfacial Nitrate Activation Toward Efficient Electrochemical Ammonia...

The electrochemical nitrate-to-ammonia conversion (NO₃RR) offers a sustainable route for nitrogen utilization, yet its efficiency is limited by poor nitrate adsorption and sluggish reaction kinetics. Here, a mesoporous FeO_x electrocatalyst (meso-FeO_x) with dual geometric and electronic optimization is presented for enhanced NO₃RR performance. Through an in situ electrochemical preactivation strategy (-1.3 V vs. RHE), the resulting FeO_x catalyst, meso-FeO_x-e1.3, achieves a great ammonia yield rate of 255.40 μmol cm^-2 h^-1 with a Faradaic efficiency for ammonia (FE_NH3) of 91.63% at -1.0 V versus RHE, outperforming most previously reported Fe-based catalysts. X-ray photoelectron spectroscopy and theoretical calculations reveal that cathodically tuned Fe³⁺/Fe²⁺ redox pairs dynamically regulate the adsorption and activation of nitrate, while the well-defined mesoporous structure ensures efficient mass transport. This work demonstrates a synergistic design principle-combining nanostructural engineering with dynamic electronic modulation, to enhance the multistep electrocatalysis reaction.