CF bonding in fluorinated N-Doped carbons

Highlights: • N-doped porous carbons displaying different properties were fluorinated. • The total N content remains unchanged during fluorination. • Fluorination does not decrease drastically the specific surface area. • A huge decomposition in F₂ gas is avoided by the use of mild conditions. Porous carbons are used in various applications for energy storage. Nitrogen doping of these carbons modifies their electrochemical and chemical properties and co-doping them with fluorine atoms, appears as a promising route to further tailor their physical and chemical properties. The present paper focuses on the gas/solid fluorination with molecular fluorine (F₂) of various types of N-doped porous carbons. The consequences of the fluorination on the porosity of these materials were studied as well as their CF bonding type. Mild conditions avoid a huge decomposition in F₂ gas of these materials and a drastic decrease of their specific surface area. Micropores, which are hosting most of the FeNx catalytic sites, are the most affected by fluorination, and a new N1s XPS peak assigned to pyridinic-N---CF has been identified, coinciding with that of the XPS binding energy of N1s in FeNx. However, molecular fluorine did not react directly with nitrogen atoms in these materials, whatever their type since no NF containing volatile products were evolved during the treatment. Finally, a dual CF bonding, characterized by the coexistence of CF bonds with weakened covalence and covalent CF, is evidenced in all fluorinated N-doped porous carbons.