Abstract
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 practical 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 (FeCl3) and pore formation agent (ZnCl2) 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 m2 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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