Atomically Dispersed CoN₄/B, N-C Nanotubes Boost Oxygen Reduction in Rechargeable Zn-Air Batteries

Minimizing the particle size of transition metals and constructing heteroatom-co-doped carbon with a high surface area are deemed imperative in maximizing the atomic utilization of carbon-based materials. Herein, the atomically dispersed Co sites anchored on interconnected B, N-doped carbon nanotubes (B, N, Co/C nanotubes) are prepared through facile molten-salt-assisted pyrolysis of B/N/Co precursors following chemical etching. The Co single atom is demonstrated to form a Co-N₄ planar configuration by XAFS analysis. The developed B, N, Co/C nanotubes exhibit excellent oxygen reduction reaction (ORR) performance in alkaline medium. They not only display a positive half-wave potential (E_1/2, 0.87 V), surpassing that of commercial Pt/C (0.84 V), but also show an outstanding stability (only 1 mV degrade can be observed after 10,000 cycles) and a high fuel selectivity. These excellent ORR performances derive from the efficient synergy of atomically dispersed Co active sites, unique 3D tubelike assembly structure, large specific surface area, and high graphitization degree. Moreover, the B, N, Co/C nanotubes assisted by RuO₂ as an air cathode can enable rechargeable Zn-air batteries with larger power density (125.0 mW cm^-2), higher specific capacity (746.8 mA h g_Zn ^-1), and better cycling stability than those of conventional Pt/C + RuO₂-based Zn-air batteries.