Designed Catalytic Templates for the Universal Synthesis of Metal/Nitrogen-Doped Carbon Nanotubes with Hierarchical Architectures for Enhanced Oxygen Reduction

Hierarchical nitrogen-doped carbon nanotubes (NCNTs) with embedded metal species (M/NCNTs) offer broad applications yet are challenging to synthesize controllably. We report a universal one-step strategy leveraging the designed catalytic templates that catalyze the growth of NCNTs and concurrently direct their assembly into diverse hierarchical architectures. This method applies to various precursors from metal hydroxides to metal-organic frameworks and metal nanoparticles/carbon, yielding M/NCNTs with morphologies from plates to flowers, spheres, and NCNTs-grafted dodecahedrons. The Co/NCNTs with hierarchical architecture exhibits superior oxygen reduction reaction (ORR) performance with a half-wave potential of 0.851 V and high durability (negligible decay after 10,000 cycles) in alkaline relative to commercial Pt/C. Electrochemical impedance spectroscopy analysis implies that the hierarchical architecture reduces the mass transfer resistance. Consequently, this Co/NCNTs enables the zinc-air battery with a peak power density of 234.1 mW cm⁻² and a specific capacity of 798.8 mAh g⁻¹ _Zn.