Mechanochemical Synthesis of Polyaniline-Derived, Graphitized Hierarchical Nanocarbons for Efficient Oxygen Electrocatalysis and Zn-Air Batteries

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 FeCl₃, 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 m²/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.