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.