Core–shell Co@Co3O4 nanoparticle-embedded bamboo-like nitrogen-doped carbon nanotubes (BNCNTs) as a highly active electrocatalyst for the oxygen reduction reaction

Abstract

The current bottleneck for fuel cells and metal-air batteries lies in the sluggish oxygen reduction reaction (ORR) on the cathode side. Despite tremendous efforts, to develop a highly efficient ORR catalyst at low cost remains a great challenge. Herein, we have synthesized core–shell Co@Co₃O₄ nanoparticles embedded in the bamboo-like N-doped carbon tubes (BNCNTs) by a simple approach comprising thermal treatment of cobalt carbonate hydroxide and urea and oxidization. The ORR catalytic activities of the Co@Co₃O₄/BNCNT composites are closely dependent on the oxidization degree of the Co nanoparticles and the N content in the BNCNTs. When oxidized at 300 °C, the as-formed Co@Co₃O₄/BNCNTs-300 composite catalyst with an N/C molar ratio of ∼1.6% achieves the maximum ORR catalytic activity. The composite catalyst also exhibits a higher ORR catalytic activity than the Co₃O₄/carbon nanotube (CNT) catalyst. The tolerance for methanol molecules and the cycle stability performance of the composite catalyst are even superior to those of the highly efficient Pt/C catalyst. Such an excellent ORR catalytic activity can be ascribed to (1) the core–shell Co@Co₃O₄ nanoparticles embedded in BNCNTs, (2) the N-doping in BNCNTs, and (3) the synergetic effect of (1) and (2) on Co₃O₄ firmly attached to both Co nanoparticles and BNCNTs, resulting in accelerated electron transport and enhanced charge delocalization.