Ambient Electrochemical Nitrogen Fixation over a Bifunctional Mo–(O–C₂)₄ Site Catalyst

The electrochemical synthesis of NH₃ and NO₃^– by the N₂ reduction reaction (NRR) and the N₂ oxidation reaction (NOR) under ambient conditions utilizing H₂O as the hydrogen and oxygen source has aroused great attention. Here, we report the fabrication of oxygen-coordinated molybdenum (Mo) single atoms anchored on carbon (Mo–O–C) using bacterial cellulose (BC) as the impregnation regulator and carbon source. As a result, the as-synthesized Mo–O–C as an electrocatalyst exhibits superior bifunctional NRR and NOR activities with high stability. A superb NH₃ yield rate of 248.6 ± 12.9 μg h^–1 mg_cat.^–1 and a faradaic efficiency (FE) of 43.8 ± 2.3% can be obtained at −0.20 V (vs RHE) by the Mo–O–C-catalyzed NRR, and Mo–O–C can also afford a NO₃^– yield rate of 217.1 ± 13.5 μg h^–1 mg_cat.^–1 with a FE of 7.8 ± 0.5% at 2.35 V (vs RHE) for the NOR. The synchrotron-based X-ray absorption spectra and theoretical calculation results unveil that the O-coordinated molybdenum configuration of Mo–(O–C₂)₄ anchored on carbon is the most stable single-atom structure as the catalytic active sites for N₂ adsorption, activation, and bifunctional hydrogenation/oxidation reactions.