Epitaxial Fe Coating on Single- and Few-Layer Mo2C MXene as Highly Efficient Catalyst for Ambient Electrochemical Ammonia Synthesis.

Iron-intercalated Mo2C MXene (Fe/Mo2C) is presented as a robust, earth-abundant electrocatalyst for ambient ammonia synthesis. An in situ HF protocol converts Mo2Ga2C MAX into few-layer Mo2C terminated with =O/-F groups; subsequent wet impregnation followed by mild reduction deposits 7 wt % Fe(0) as an epitaxial coating that lines the internal van der Waals galleries and simultaneously blankets the external basal planes of the Mo2C MXene. Aberration-corrected STEM, FFT/inverse-FFT analysis, and STEM-EDX depth profiling verify lamellar Fe domains that connect neighboring Mo2C sheets while preserving crystallinity. This hybrid architecture halves the charge-transfer resistance (EIS) and provides a high density of Fe sites that preferentially adsorb N2 over protons. In neutral 0.1 M Na2SO4, the optimized material achieves a Faradaic efficiency of 28.8% and an NH3 yield of 19.1 μmol h-1 mgFe -1 at 0.25 V vs RHE, matching or surpassing noble-metal benchmarks under ambient conditions. Operando ATR-SEIRAS detects N-N and -NH x vibrations consistent with an associative pathway, and 15N2 labeling confirms the nitrogen source. The catalyst maintains stable performance for 10 h with no detectable Fe leaching. Thus, the combination of the activity of Fe overlayers with the conductive, mechanically resilient Mo2C framework renders a material with remarkable electrocatalytic activity for green-ammonia production.