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Nitrogen-containing nanocarbons serve as pivotal catalysts in oxygen electrocatalysis and metal-air batteries. Simultaneously enhancing their N-doping level and graphitization is crucial for boosting the catalytic performance and long-term stability. Herein, we report a new mechanochemical polymerization tandem carbonization strategy for designing nitrogen-containing 3D hierarchically structured nanocarbons (N-HNCs), which were constructed from bottom-to-top packing of primary 2D nanocarbon building units. The synthesis includes mechanochemical polymerization of aniline (ANI) initiated with anhydrous FeCl 3, controllable carbonization of resultant polyaniline (PANI), and acid etching for removal of Fe species. The prepared N-HNCs possess large Brunauer–Emmett–Teller (BET) surface areas (240–988 m 2 /g), enhanced graphitization, high nitrogen content with tunable structures, abundant nanochannels for mass transportation, and versatile interfaces for ion diffusion. Thus, the N-HNCs were employed as efficient and durable electrocatalyst in both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). For instance, the N-HNCs gave a Pt/C-like half-wave potential (0.846 V) in the ORR, which was impressive among metal-free electrocatalysts. The N-HNCs can be further fabricated as an air cathode for rechargeable flow and flexible Zn-air batteries (ZABs), showing high maximum power density (185.1 mW·cm –2 ) and specific capacity (808.17 mAh·g Zn –1 ), extraordinary long-term cycle durability (>400 h), and improved roundtrip energy efficiency at 60.8% at 5 mA·cm –2 .
Qu et al. (Thu,) studied this question.