Fe-Cluster Pushing Electrons to N-Doped Graphitic Layers with FeC(Fe) Hybrid Nanostructure to Enhance O Reduction Catalysis of Zn-Air Batteries.

Non-noble metal catalysts with catalytic activity toward oxygen reduction reaction (ORR) comparable or even superior to that of Pt/C are extremely important for the wide application of metal-air batteries and fuel cells. Here, we develop a simple and controllable strategy to synthesize Fe-cluster embedded in FeC nanoparticles (designated as FeC(Fe)) encased in nitrogen-doped graphitic layers (NDGLs) with graphitic shells as a novel hybrid nanostructure as an effective ORR catalyst by directly pyrolyzing a mixture of Prussian blue (PB) and glucose. The pyrolysis temperature was found to be the key parameter for obtaining a stable FeC(Fe)@NDGL core-shell nanostructure with an optimized content of nitrogen. The optimized FeC(Fe)@NDGL catalyst showed high catalytic performance of ORR comparable to that of the Pt/C (20 wt %) catalyst and better stability than that of the Pt/C catalyst in alkaline electrolyte. According to the experimental results and first principle calculation, the high activity of the FeC(Fe)@NDGL catalyst can be ascribed to the synergistic effect of an adequate content of nitrogen doping in graphitic carbon shells and Fe-cluster pushing electrons to NDGL. A zinc-air battery utilizing the FeC(Fe)@NDGL catalyst demonstrated a maximum power density of 186 mW cm, which is slightly higher than that of a zinc-air battery utilizing the commercial Pt/C catalyst (167 mW cm), mostly because of the large surface area of the N-doped graphitic carbon shells. Theoretical calculation verified that O molecules can spontaneously adsorb on both pristine and nitrogen doped graphene surfaces and then quickly diffuse to the catalytically active nitrogen sites. Our catalyst can potentially become a promising replacement for Pt catalysts in metal-air batteries and fuel cells.