Oxygen Reduction Reaction Catalyzed By Metal-Nitrogen-Carbon Hybrids Derived From Metal-Organic Frameworks: Optimized Performance By Zinc Porogen

Carbon-based nanocomposites have been attracting extensive attention as viable candidates to replace platinum in the electrocatalytic reduction of oxygen, a critical process at fuel cell cathode. One unique system is carbon-supported iron carbide (Fe3C/C) catalysts derived pyrolytically from metal organic frameworks ( MOFs). Herein, a series of Fe3C/C nanocomposites were produced by pyrolysis at a controlled temperature of FeMOF-NH2 with a systemic variation of the iron and zinc compositions in the MOF precursor. Scanning/transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction measurements were carried out to examine the morphologies, structures, and elemental composition of the nanocomposites, while nitrogen adsorption/desorption and Raman studies were carried out to evaluate the surface area and porosity. The results showed that an optimal zinc to iron feeding ratio was required to prepare a catalyst with a preferential pore size distribution. In electrochemical measurements, the sample derived from 20% zinc replacement in the FeMOF-NH2 precursor exhibited the best activity in the electrocatalytic reduction of oxygen in alkaline electrolytes 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.