Dual-template strategy for electrocatalyst of cobalt nanoparticles encapsulated in nitrogen-doped carbon nanotubes for oxygen reduction reaction

Abstract

Development of non-precious metal catalysts (NPMCs) with high performance and stability has important value for oxygen reduction reaction (ORR) of fuel cells. In this paper, a novel structure of nitrogen-doped carbon nanotubes-encapsulated cobalt nanoparticles (Co@NCNTs) is synthesized by a simple dual-template strategy using silica colloid and tri-block copolymer (polyethylene oxide-polypropylene oxide-polyethylene oxide, PEO-PPO-PEO, F127) as hard and soft templates, respectively. The Co@NCNTs-800 synthesized at 800 °C shows an excellent ORR performance, which can be attributed to the desirable combination of their unique one-dimensional carbon nanotube structure, the adequate nitrogen doping level, the large surface area created by the dual-template strategy, and the synergistic effect between graphitic carbon layer and cobalt nanoparticles. The doped N atoms can provide coordination sites for cobalt nanoparticles and form NC moieties as dominant active sites, which provide positive effect on catalytic ORR activity. The graphitic carbon layers can protect cobalt nanoparticles against agglomeration and electrolyte corrosion, while cobalt nanoparticles can activate the bordering graphitic carbon layers and further increase ORR activities. This dual-template synthetic strategy provides an opportunity to promote the catalytic performance of NPMCs for application of polymer electrolyte membrane fuel cells.