From Cyano-aromatic Molecules to Nitrogen-doped Carbons by Solution Plasma for the Oxygen Reduction Reaction in Alkaline Medium

Nitrogen-doped carbon nanoparticles (NCNPs) were synthesized by a solution plasma process followed by a thermal annealing at 900°C. Cyano-aromatic molecules, including cyanobenzene (C₇H₅N), 2-cyanopyridine (C₆H₄N₂), and cyanopyrazine (C₅H₃N₃), were used as single source precursors for the synthesis. The morphological features of NCNPs were governed by the aggregates and agglomerates of uniform nanosized particles (20-40nm). The structural analyses confirmed that NCNPs mainly exhibited a disordered amorphous carbon structure. The nitrogen doping contents determined from an X-ray photoelectron spectroscopy were found to be 0.58, 1.36, and 1.29 at% for NCNPs synthesized from cyanobenzene, 2-cyanopyridine, and cyanopyrazine, respectively. The improvements of oxygen reduction reaction activity and selectivity toward a four-electron pathway in an alkaline solution of NCNPs were correlated with the nitrogen doping content and nitrogen bonding state. The NCNPs also possessed excellent long-term durability and strong methanol tolerance in an alkaline solution compared to those of a commercial Pt/carbon catalyst.