Lang Xiao, Wanqing Yu, Jing Liu ^*, Shankui Luan, Wenyu Pei, Xuejing Cui, Luhua Jiang^*

College of Materials Science and Engineering, Qingdao University of Science and Technology,

Qingdao, Shandong 266042, China.

Abstract: Developing an efficient and stable non-precious metal catalyst (NPMC) for oxygen reduction reaction (ORR) is crucial for Zn-air batteries. Herein, we report a super-molecule self-scarifying template and confinement pyrolysis strategy to obtain an efficient ORR catalyst of well-dispersed Co₃Fe₇/CoC_x heterostructure nanoparticles encapsulated by nitrogen-doped carbon nanotubes (Co₃Fe₇/CoC_x@N-CNT). The as-synthesized Co₃Fe₇/CoC_x@N-CNT catalyst exhibits outstanding ORR activity, with a half-wave potential of 0.88 V versus a reversible hydrogen electrode (vs. RHE) and good stability. The Zn-air battery based on the Co₃Fe₇/CoC_x@N-CNT cathode achieves a peak power density of 265 mW cm^-2 and extra-long durability over 200 hours, which is superior to most of the reported NPMCs and even the Pt/C counterpart. The physical characterization and electrochemical poisoning experiments discover that Co₃Fe₇/CoC_x nanoparticles in the core along with pyridine N and Fe-N_x hosted in the carbon nanotube all act as active sites for the ORR. Further theoretical calculation demonstrates charge redistribution between the Co₃Fe₇/CoC_x nanoparticles and the Fe-N_x carbon overlayers downshift d-band center of Fe and optimize the adsorption, which boosts the ORR kinetics. This work provides an effective strategy to synthesize non-precious metal ORR catalysts with multiple active sites and highlights the synergistic role of encapsulated nanoparticles and carbon support.

Keywords: Heterostructure; Oxygen reduction reaction; Confined pyrolysis; Zn-air battery; Synergistic catalysis

*Corresponding authors: liuj955@qust.edu.cn; luhuajiang@qust.edu.cn (L. Jiang)

https://doi.org/10.1016/j.jcis.2023.11.034