Nitrogen-coordinated iron atoms on carbon supports(Fe-N-C)are among the most promising noble-metal-free electrocatalysts for oxygen reduction reaction(ORR).However,their unsatisfactory stability limits their prac-tical application.Herein,we demonstrate a dual-shell Fe-N-C electrocatalyst with excellent catalytic activity and long-term stability.Pyrrole and dopamine are sequentially polymerized on a fumed silica nanoparticle template.Metal precursor(FeCl_(3))and pore formation agent(ZnCl_(2))were loaded on the inner polypyrrole shell.During carbonization,the Zn evaporation creates abundant mesopores in the polydopamine-derived outer carbon shell,forming a "chain mail"like outer shell that protects Fe-N-C active sites loaded on the inner carbon shell and enables efficient mass transfer.Systematical tuning of the shield thickness and porosity affords the optimal electrocatalyst with a large surface area of 934 m^(2)g^(-1) and a high Fe loading of 2.04 wt%.This electrocatalyst delivers excellent ORR activity and superior stability in both acidic and alkaline electrolytes.Primary Zn-air batteries fabricated from this electrocatalyst delivers a high-power density of 257 mW cm^(-2) and impressive durability of continuous discharging over 250 h.Creating a graphitic and porous carbon protective shell can be further extended to other electrocatalysts to enable their practical applications in energy conversion and storage.
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