CoFe Alloy-Coupled Mo2C Wrapped by Nitrogen-Doped Carbon as Highly Active Electrocatalysts for Oxygen Reduction/Evolution Reactions

Molybdenum carbide (Mo2C) with a Pt-like d-band electron structure exhibits certain activities for oxygen reduction and evolution reactions (ORR/OER) in alkaline solutions, but it is questioned due to its poor OER stability. Combining Mo2C with transition metals alloy is a feasible way to stabilize its electrochemical activity. Herein, CoFe-Prussian blue analogues are used as a precursor to compound with graphitic carbon nitride and Mo6+ to synthesize FeCo alloy and Mo2C co-encapsulated N-doped carbon (NG-CoFe/Mo2C). The morphology of NG-CoFe/Mo2C (800 degrees C) shows that CoFe/Mo2C heterojunctions are well wrapped by N-doped graphitic carbon. Carbon coating not only inhibits growth and agglomeration of Mo2C/CoFe, but also enhances corrosion resistance of NG-CoFe/Mo2C. NG-CoFe/Mo2C (800 degrees C) exhibits an excellent half-wave potential (E-1/2 = 0.880 V) for ORR. It also obtains a lower OER overpotential (325 mV) than RuO2 due to the formation of active species (CoOOH/beta-FeOOH, as indicated by in-situ X-ray diffraction tests). E-1/2 shifts only 6 mV after 5000 ORR cycles, while overpotential for OER increases only 19 mV after 1000 cycles. ORR/OER performances of NG-CoFe/Mo2C (800 degrees C) are close to or better than those of many recently reported catalysts. It provides an interfacial engineering strategy to enhance the intrinsic activity and stability of carbides modified by transition-metals alloy for oxygen electrocatalysis.

Automated summary

Alloying with transition metals is a feasible way to enhance the electrochemical activity and stability of molybdenum carbide. The composite NG-CoFe/Mo2C was synthesized by combining CoFe-Prussian blue analogues with graphitic carbon nitride and Mo6+. It exhibited excellent ORR and OER performances and provided a strategy to improve the stability of molybdenum carbide in oxygen electrocatalysis.