Carbon-based nanocomposites have been attracting extensive attention as high-performance catalysts in alkaline media towards the electrochemical reduction of oxygen. Herein, polyacrylonitrile nanoflowers are synthesized via a free-radical polymerization route and used as a structural scaffold and precursor, whereby controlled pyrolysis leads to the ready preparation of carbon nanocomposites (FeNi-NCF) doped with both metal (Fe and Ni) and nonmetal (N) elements. Transmission electron microscopy studies show that the FeNi-NCF composites retain the flower-like morphology, with the metal species atomically dispersed into the flaky carbon petals. Remarkably, despite a similar structure, elemental composition, and total metal content, the FeNi-NCF sample with a high Fe:Ni ratio exhibits an electrocatalytic performance towards oxygen reduction reaction (ORR) in alkaline media that is similar to that by commercial Pt/C, likely due to the Ni to Fe electron transfer that promotes the adsorption and eventual reduction of oxygen, as evidenced in X-ray photoelectron spectroscopic measurements. Results from this study underline the importance of the electronic properties of metal dopants in the manipulation of the ORR activity of carbon nanocomposites.
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Oxygen Reduction Reaction Catalyzed by Metal-Nitrogen-Carbon Hybrids Derived from Metal-Organic Frameworks: Optimized Performance by Zinc Porogen
Carbon-based catalysts have been attracting extensive attention as viable candidates to replace platinum towards oxygen reduction reaction, a critical process at fuel cell cathode. An advancement has been the development of carbon-supported iron carbide (Fe3C/C) catalysts derived from the pyrolysis of metal organic frameworks (MOFs). In the present study, a series of Fe3C/C nanocomposites were prepared by controlled pyrolysis of FeMOF-NH2 with a systemic variation of the iron and zinc compositions in the MOF precursor. Scanning/transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopic measurements were carried out to examine the morphologies, structures, and elemental composition of the nanocomposites, while nitrogen adsorption/desorption and Raman studies were used to characterize the surface area and porosity. It was found that an optimal zinc to iron feeding ratio was required to produce a catalyst with a preferential pore size distribution. Electrochemical measurements revealed that the sample derived from 20% zinc replacement in the FeMOF-NH2 precursor exhibited the best electrocatalytic activity in alkaline media among the series, with the most positive onset potential and highest limiting current, which coincided with the highest surface area and porosity. The results suggest that deliberate structural engineering is critical in manipulating and optimizing the electrocatalytic activity of metal,nitrogen-codoped carbon nanocomposites.
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- Award ID(s):
- 1900235
- NSF-PAR ID:
- 10205968
- Date Published:
- Journal Name:
- Science of advanced materials
- ISSN:
- 1947-2935
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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