Controlled introduction of defects into single-walled carbon nanotubes via a fluorination-defluorination strategy using xenon difluoride and their alkaline oxygen reduction reaction catalytic activity

Abstract

The defect edges in carbon nanomaterials have attracted attention as catalytic active sites for the oxygen reduction reaction (ORR) of the cathode in electrolyte fuel cells, and the defect control in carbon nanomaterials is becoming increasingly important. This study evaluates a fluorination-defluorination strategy for the controlled introduction of defects into single-walled carbon nanotubes (SWCNTs) involving the fluorination of SWCNTs using xenon difluoride (XeF₂) and their subsequent defluorination through thermal annealing. We synthesized fluorinated SWCNTs with different fluorine contents using gaseous XeF₂ and annealed the fluorinated SWCNTs at 1000 °C for 3 h under nitrogen gas flow. Structural analyses revealed that SWCNTs derived from fluorinated SWCNTs with low fluorine contents primarily had single point defects. In contrast, SWCNTs derived from fluorinated SWCNTs with high fluorine contents had vacancy defects with edges. According to the ORR catalyst evaluation in alkaline aqueous solution, SWCNTs with edge defects, rather than point defects, can improve the efficiency of ORR catalytic activity. The proposed fluorination-defluorination strategy using gaseous XeF₂ is expected to enable the controlled introduction of defects in different types of carbon materials.

Keywords: Defect control; Defluorination; Fluorination; Single-walled carbon nanotubes; Xenon difluoride.