Nitrogen and fluorine co-doped graphite nanofibers as high durable oxygen reduction catalyst in acid

Fluorine doping to the GNF dramatically changes the nanofiber structure to graphene heets. Nitrogen and fluorine co-doped graphite nanofibers (N–F/GNFs) were synthesized usingmelamine and ammonium fluoride as precursors, respectively, for use as metal-free catalystsfor oxygen reduction reaction (ORR). The N–F/GNF catalyst undergoes structural transformationresulting in wrinkled graphene structures with many open-edge sites when F isdoped into N/GNF. The developed catalyst has no effect on CH3OH or CO, which makes ithighly desirable as a metal-free electrocatalyst for the ORR. The developed catalyst wassubjected to 20,000 repeated potential cycles, no degradation of ORR activity was observedin acidic media. X-ray photoelectron spectroscopy analysis of the N–F/GNF catalyst revealsthe presence of active pyridine and graphitic type N with highly active semi-ionic C–F bondin the graphitic structure. First-principles density functional theory calculations furthersupport the formation of graphene structures from the GNF with the interlayer distanceincreasing from 3.9 to 5.1A°. The Bader charge analysis predicts the site specificity of Fdoping in N-doped GNF.