Double-Phase Heterostructure within Fe-Doped Cu_2–<i>x</i>S Quantum Dots with Boosted Electrocatalytic Nitrogen Reduction

Abstract

Electrochemical nitrogen reduction reaction (NRR) is considered as one of the most promising methods for NH3 synthesis under room temperature and ambient pressure. A grand challenge of NRR is the development of efficient electrocatalysts, for which the delicate nanostructuring of catalysts plays an important role. Herein, a series of Fe-doped Cu2–xS quantum dots (QDs) are synthesized with multiple active sites and interface engineering, in which the double-phase heterostructure plays a key role for boosting NRR activity. The yield of NH3 was obviously improved with the increase of Fe content from 0 to 3% but started to decrease with Fe from 3 to 9%. The optimized Fe3%–Cu2–xS QDs show an outstanding NH3 yield of 26.4 μg h–1 mg–1cat at −0.7 V (vs the reversible hydrogen electrode), which is 5 times higher than that of Cu2–xS QDs. More importantly, we observed that the highest NRR activity in Fe3%–Cu2–xS QDs was ascribed to the formation of an inherent double-phase heterostructure of Cu2–xS/Cu5FeS4, whereas the complete conversion to single-phase Cu5FeS4 with increased Fe doping (9%) resulted in the activity decrease. Further, N2 temperature-programmed desorption and electrochemical impedance spectra characterizations confirm the stronger chemical adsorption of N2 and faster charge transfer in the Cu2–xS/Cu5FeS4 QDs. A plausible mechanism was proposed for the double-phase Cu2–xS/Cu5FeS4 heterostructure, where the interface provides efficient charge transfer and more active sites of Cu, Fe, and S for the synergetic adsorption and activation of N2. Our work provides a simple strategy for the design of NRR electrocatalysts, which may also bring new inspiration for the preparation of the inherent double-phase heterostructure within other doped QDs.