Pyridinic

Pyridinic refers to a type of nitrogen configuration found in nitrogen-doped carbon materials, where a nitrogen atom substitutes a carbon at an edge or defect and adopts a pyridine-like environment. It is one of the common nitrogen functionalities described in doped graphitic systems, alongside pyrrolic and graphitic (quaternary) nitrogen.

In pyridinic sites, nitrogen is typically sp2-hybridized and bonds to two carbon atoms at the edge of the graphitic lattice. The nitrogen’s lone pair resides outside the π-system, which gives pyridinic N basic character and can influence local electronic structure. This contrasts with pyrrolic nitrogen, which resides in five-membered rings and contributes differently to the π-system, and graphitic nitrogen, which is embedded within the graphene plane and bonded to three carbons.

Pyridinic nitrogen is often implicated as an active site for catalytic processes, particularly the oxygen reduction reaction (ORR) in alkaline media. By altering charge distribution and providing a favorable adsorption site for O2, pyridinic N can enhance catalytic activity and electron transfer. It can also coordinate with metal species, supporting the development of single-atom catalysts on carbon supports.

Characterization of pyridinic nitrogen commonly uses X-ray photoelectron spectroscopy (XPS), where the N 1s binding energy for pyridinic N typically appears near about 398–399 eV, though exact values can vary with the chemical environment. The relative abundance of pyridinic versus other nitrogen functionalities depends on synthesis conditions, including precursor choice and heat treatment, influencing material properties in energy storage, sensing, and catalysis applications.