MOF-Derived Isolated Fe Atoms Implanted in N-Doped 3D Hierarchical Carbon as an Efficient ORR Electrocatalyst in Both Alkaline and Acidic Media

In order to improve the catalytic performance of oxygen reduction reaction (ORR), it is pivotal to increase the density and accessibility of the active sites. Herein, we have developed a template-free melamine-assisted cocalcined strategy to afford Fe-embedded and N-doped carbons (Fe-N-C) with not only high density of atomically dispersed Fe-Nx active sites but also abundant three-dimensional interconnected mesopores by directly pyrolyzing Fe-ZIF-8 covered with a controllable melamine layer. It is demonstrated that the introduction of melamine in the precursor plays a key role in constructing various carbonized products with controllable morphology, porosity, and components. With an optimal mass ratio 1:1 of melamine to Fe-ZIF-8, the resultant Fe@MNC-1 exhibits excellent ORR activity and stability, which exceeds 20 wt % commercial Pt/C catalyst (with a half-wave potential of 0.88 V vs 0.85 V) in an alkaline electrolyte and is even comparable to the commercial Pt/C catalyst (with a half-wave potential of 0.78 V vs 0.80 V) in an acidic electrolyte. To the best of our knowledge, Fe@MNC-1 can be ranked among the best nonprecious metal electrocatalysts for ORR in both alkaline and acidic media. The present synthetic strategy may provide a new opportunity for the design and construction of metal-organic framework-derived nanomaterials with rational composition and a desired porous structure to boost their electrocatalytic performance.