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

Abstract

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 °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 °C) exhibits an excellent half-wave potential (E1/2 = 0.880 V) for ORR. It also obtains a lower OER overpotential (325 mV) than RuO2 due to the formation of active species (CoOOH/β-FeOOH, as indicated by in-situ X-ray diffraction tests). E1/2 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 °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.

Application of changing the valence state of metals through the reaction time for efficient oxygen evolution reaction

“…Hence, developing inexpensive, stable, and highly efficient catalysts for the OER is still extre-mely needed. Based on this, non-noble metals such as carbides, 9,10 phosphides, 11,12 nitrides, 13,14 oxides, 15,16 hydroxides, 17,18 and sulfides 19,20 have been extensively studied and applied in the OER.…”

A Perspective on Protective Carbon Shells for Improved Stability of Alkaline Water Oxidation Electrocatalysts

“…Recently, researchers have begun to employ carbon shells to protect electrocatalytic OER core structures from oxidation under alkaline conditions. Essentially, the carbon shell can limit electrolyte contact with the electrocatalytic core, while also imparting improved electrical conductivity, increased electrochemically active surface area, and providing additional active sites for OER electrocatalysis. − These carbon shell–core materials have been implemented as metal and transition metal nanoparticles encased in carbon, including metal carbides, metal phosphides, metal sulfides, MXenes, and other unique structures. − ,− While the carbon shells for these materials are reported as imparting stability, thermodynamic considerations and recent studies on carbon corrosion contradict this finding. − …”