Cobalt-Embedded Nitrogen-Doped Carbon Nanotubes as High-Performance Bifunctional Oxygen Catalysts

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are key processes in various renewable-energy technologies and call for high-performance bifunctional ORR/OER electrocatalysts. In this study, a highly efficient bifunctional oxygen catalyst, which was made of bamboo-like nitrogen-doped carbon nanotubes with embedded cobalt nanoparticles (Co@NCNTs), was fabricated by a one-step pyrolysis route. Systematic electrochemical results demonstrated that the optimized electrocatalyst only needed a small potential hysteresis of about 0.834 V to achieve 1 mAcm(-2) ORR current and 10 mAcm(-2) OER current, and simultaneously gave superior stability and methanol tolerance to those of commercial metal catalysts. The major factors that influenced the bifunctional catalyst performance of Co@NCNTs are discussed, among which the nitrogen chemical state and metal element play important roles. Moreover, the catalyst showed good activity and stability in rechargeable zinc-air batteries, which indicated their potential applications in metal-air batteries, fuel cells, and water-splitting devices.