High-performance Fe-N-C electrocatalysts with a "chain mail" protective shield

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 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.