Fe-Mo-catalyzed nitrate reduction: A biomimetic approach to green ammonia production

Electrocatalytic nitrate reduction reaction (eNO₃RR) presents an innovative approach to achieve green NH₃ synthesis and mitigate environmental NO₃⁻ pollution. However, the bottleneck for large-scale application of eNO₃RR is the development of efficient electrocatalysts. Herein, inspired by the structure of nitrogenase and nitrate reductase, a novel Fe-Mo-based electrocatalyst (FeMoS-O) with distinctive bimetallic Fe-O-Mo active centers was developed using FeMo₂S₄ as the precursor via in situ electrochemical activation to induce surface O-doping. Combining comprehensive in situ characterizations and theoretical calculation results reveal that the Fe and Mo sites of the Fe-O-Mo center are responsible for the hydrogenation of NO_x species and the dissociation of H₂O, respectively, which is similar to the working mechanism of nitrate reductase. Meanwhile, O-doping on the Fe-O-Mo surface significantly reduces the energy barriers of the rate-determining steps of these two processes. As feedback, the synergistic effect of Mo and Fe sites endows the resultant FeMoS-O with excellent eNO₃RR performance under neutral conditions, with high faradaic efficiency (> 90%) in a potential window exceeding 0.50 V, large partial current density and yields, as well as quite good stability towards NH₃ production. This work provides new insights into the preparation of more advanced enzyme-mimicking catalysts.