Boosting Oxygen Reduction Catalysis with N-doped Carbon Coated Co9S8 Microtubes.

Herein, nitrogen-doped carbon coated hollow Co9S8 microtubes (Co9S8@N-C microtubes) are prepared through a facile solvothermal procedure, followed by dopamine polymerization process together with a post-pyrolysis which present excellent electrocatalytic activity for oxygen reduction reaction (ORR). The Co9S8 within the hollow Co9S8@N-C microtubes presents a well-defined single-crystal structure with dominated (022) plane. To obtain desired electrocatalyst, the annealing temperature and the thickness of carbon layer tuned by changing the dopamine concentration are optimized systematically. The electrochemical results demonstrate that the coordination of the N-doped carbon layer, exposed (022) plane, and hollow architecture of Co9S8 microtubes calcined at 700 °C affords outstanding ORR performance to Co9S8@N-C microtubes. The moderate thickness of the carbon layer is crucial for improving ORR activity of Co9S8@N-C microtubes, while increasing or decreasing the thickness would result in activity decrease. More importantly, the N-doped carbon layer can protect inner Co9S8 from undergoing aggregation and dissolution effectively during the ORR, resulting in excellent electrocatalytic stability.