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 NOx 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.