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Boosting Faradic efficiency of dinitrogen reduction on the negatively charged Mo sites modulated via interstitial Fe doping into a Mo2C nanowall catalyst
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•Interstitial Fe doping into Mo2C electrocatalyst was proposed to enhance Faradic efficiency of eNRR.•The negatively charged Mo sites is established as the chemical origin of high Faradic efficiency.•A surface hydrogen generation mechasim is confirmed by DFT calcualtions.•The Faradic efficiency of eNRR on Mo2C is doubled by interstitial Fe doping.•An improved electrochemical stablity is also observed on interstitial Fe doping into Mo2C.
The electrochemical nitrogen reduction reaction (eNRR) provides a sustainable way to generate ammonia (NH3) but its Faradaic efficiency (FE) is relatively low and could be further improved, especially on the highly active molybdenum carbide (Mo2C) electrocatalyst. Our theoretical calculations suggest that unlike substitute doping model, interstitial Fe doping into Mo2C is highly eNRR-selective due to decreasing hydrogen evolution activity and unique surface-hydrogenation mechanism on negatively charged Mo sites around Fe atoms. Inspired by this prediction, we successfully developed a novel interstitial Fe doped Mo2C electrocatalyst by the pyrolysis of Fe-doped Mo/Zn bimetallic imidazolate frameworks (Fe-Mo/Zn BIFs) as a precursor where Fe atoms substitute Zn sites to obtain the spatial confinement effect. When evaluated in eNRR catalysis, Fe/Mo2C catalyst therefore exhibits a much higher FE of 20.1% at −0.45 V vs. RHE (reversible hydrogen electrode), which is almost double that of pristine Mo2C and substitute type. Moreover, the Fe/Mo2C catalyst also exhibits high ammonia yield rate with excellent durability over the six continuous cycles.