Unveiling the inter-molecular charge transfer mechanism of N-doped graphene/carbon nanotubes heterostructure toward oxygen reduction process for Zn-air battery

Heteroatom-doped carbon-based materials have been deemed as highly efficient electrocatalysts for cathodic oxygen reduction reaction (ORR) in the sustainable energy conversion technologies. However, the limited active sites caused by the aggregation of carbon layers ineluctably hinder the mass transfer, thereby generating insufficient ORR performance. Herein, we offer a rational and facile method to manufacture a hybrid hetero-structure of N-doped graphene and carbon nanotubes at the pyrolysis temperature of 900 degrees C (N-G/CNTs-900), which exhibits a better ORR activity than most of reported carbon-based ORR electrocatalysts, and comparable to that of Pt/C. Thus-fabricated N-G/CNTs-900 features hierarchically porous architecture, high specific surface area, abundant defects, and high active N content, and what's more, it also affords active sites for oxygen activation and subsequent 4e(-) reduction processes due to the hetero-interlayer charge transfer and the electron accumulations of the carbon atoms on the surface layer by theoretical calculations. Compared with commercial Pt/C, N-G/CNTs-900-based Zn-air battery presents a higher peak power density (133.60 mW/cm(2)) and a larger specific capacity (707 mAh/gZn). This work provides a novel idea to design the high-efficiency and long-term durability ORR catalyst, which is benefit for boosting the commercial applications of metal-free carbon-based materials in the renewable energy conversion devices.