Porous N, B co-doped carbon nanotubes as efficient metal-free electrocatalysts for ORR and Zn-air batteries

The flexible design and construction of oxygen reduction reaction (ORR) catalysts with high activity, great stability, and superior cost efficiency are essential for metal-air batteries and fuel cells. Hollow carbon nanotubes (CNTs) are considered promising electrocatalysts owing to their outstanding thermal stability, robust chemical properties, and high specific surface area. Herein, a convenient and controllable solid-phase route is proposed for the preparation of porous nitrogen (N) and boron (B) co-doped carbon nanotubes (NBCNT) by using tubular polypyrrole (PPy) and sodium tetraphenylboron ((C6H5)4BNa), in which (C6H5)4BNa serves not only as a B source but also as a pore-forming agent that can help to regulate N configuration and expose more active sites. Due to the synergistic effects of porous one-dimensional hollow structure and the binary heteroatom doping, the optimized NBCNT catalyst demonstrates superior catalytic performance for ORR in both acidic and alkaline electrolytes. Moreover, Zn-air batteries are constructed based on the as-prepared catalysts, which reveal a high operating voltage (1.43 V) and peak power density (173.93 mW cm−2), further demonstrating a comparable electrocatalytic performance of the catalysts to commercial Pt/C catalyst. This work reveals a novel construction of high-efficiency and cost-effective metal-free catalysts for various energy conversion and storage technologies.