Highly efficient metal-free electrocatalysts toward oxygen reduction derived from carbon nanotubes@polypyrrole core–shell hybrids

Abstract

Nitrogen-doped carbon nanotubes (NCNTs) are recognized as one of the most promising oxygen reduction reaction (ORR) catalysts, while developing a preparation protocol for CNT-based ORR catalysts with cost-effective synthesis, high activity and durability is still a challenge. In this work, we report the fabrication of N-doped CNT catalysts with a homogeneous distribution of dopants in the CNT matrix by pyrolysis of a core–shell nanostructured CNTs@polypyrrole nanocomposite (CNTs@PPy). The as-obtained NCNTs exhibit excellent performance in electrocatalytic oxygen reduction with an onset potential of 0.95 V vs. RHE, a diffusion-limited current of 6.82 mA cm⁻² and excellent stability in alkaline media, much superior to that of reported CNT-based ORR catalysts as well as commercial Pt/C. Moreover, the ratio of different nitrogens (pyridinic, pyrrolic and graphitic N) can be tuned easily by changing the coating amount of PPy in the CNTs@PPy core–shell precursors; and the results indicate that the pyridinic-N in the CNTs@PPy derived NCNTs plays a key role in promoting the ORR performances.