Nitrogen and fluorine hybridization state tuning in hierarchical honeycomb-like carbon nanofibers for optimized electrocatalytic ORR in alkaline and acidic electrolytes

Nitrogen and fluorine co-doped hierarchical honeycomb-like carbon nanofibers (N-F-CNFs-950) are prepared by electro-blown spinning technology and high temperature calcination. It possesses large specific surface area, micro/meso/macro hierarchical through-pore structure, high pyridine-N and graphite-N content. These characteristics make it exhibit an outstanding alkaline electrocatalytic oxygen reduction reaction (ORR) activity (half wave potential of 0.833 V vs reversible hydrogen electrode and current density of 5.48 mA cm(-2)). In particular, the introduction of the ionic C-F/N-F successfully avoids the inactivation of pyridine N in the carbon skeleton due to protonation in the acidic electrolyte. And the ionic C-F/N-F activated pyridine N work synergistically with graphite N to promote N-F-CNFs-950 to exhibit an acidic ORR activity (half wave potential of 0.606 V vs reversible hydrogen electrode and current density of 5.58 rnA cm(-2)) that is only second to commercial Pt/C. Importantly, the N-F-CNFs-950 catalyst exhibits much better methanol tolerance and electrochemical stability in both alkaline and acidic environments.