Shrimp-shell derived carbon nanodots as precursors to fabricate Fe,N-doped porous graphitic carbon electrocatalysts for efficient oxygen reduction in zinc-air batteries

In this work, shrimp-shell derived N-doped carbon nanodots (N-CNs) as carbon and nitrogen sources are assembled into particle-like aggregates by a simple polymerization reaction of pyrrole in the presence of Fe3+ to form Fe containing N-CN/polypyrrole (PPY) composites (Fe-N-CN/PPy). The resulting composites are thermally treated by a facile pyrolysis approach under a N-2 atmosphere to obtain an Fe, N-doped porous graphitic carbon (Fe-N-PGC) material. The results demonstrate that the pyrolytically converted carbon material at 800 degrees C (Fe-N-PGC-800) exhibits an approximately mesoporous structure with a pore size distribution centered at similar to 1.97 nm and similar to 2.8 nm and a surface area of 806.7 m(2) g(-1). As an electrocatalyst for oxygen reduction reaction (ORR) in alkaline media, Fe-N-PGC-800 shows superior ORR catalytic activity with an onset potential of -0.017 V and a limiting current density of 5.42 mA cm(-2) (at -0.4 V, vs. Ag/AgCl), which is superior to that of commercial Pt/C catalysts (onset potential of -0.018 V and a limiting current density of 5.21 mA cm(-2) at -0.4 V, vs. Ag/AgCl). Additionally, Fe-N-PGC-800 also exhibits good ORR activity in acidic media with an onset potential of 0.53 V and a limiting current density of 5.58 mA cm(-2) (at 0.1 V, vs. Ag/AgCl), comparable to that of most reported Fe-based N-doped carbon electrocatalysts. An air cathode made from Fe-N-PGC-800 shows high performance and superior cycling durability in zinc-air batteries (gravimetric energy density of 752 Wh kg(-1)), comparable to that of commercial Pt/C-based batteries (gravimetric energy density of 774 Wh kg(-1)). This work demonstrates the feasibility of utilizing biomass as a starting material to fabricate Fe, N-doped carbon materials as high performance ORR electrocatalysts for practical application in ORR-relevant energy devices.