Dielectric-barrier-stabilized solution plasma for high-nitrogen, few-layer graphene via low-temperature CN radical polymerization

Abstract

Nitrogen-doped graphene (NG) with high crystallinity and elevated nitrogen content is highly desirable for energy and catalytic applications, yet conventional high-temperature methods suffer from nitrogen volatilization, structural degradation, and metal contamination. Here, we report a dielectric-barrier-assisted criss-cross electrode configuration for solution plasma (SP) synthesis that achieves stable, low-temperature glow discharge in a benzene–DMF mixture. Finite-element simulations and optical diagnostics reveal that the dielectric barrier suppresses electron avalanches, producing a spatially uniform CN-rich plasma (∼2505 K) while minimizing C₂ formation, thereby preserving aromatic integrity and limiting nitrogen loss. Compared to the conventional pin-to-pin SP, which generates high-temperature (∼5280 K), C₂-dominated abnormal glow, the dielectric-stabilized system yields few-layer NG with markedly reduced defect density (I_D/I_G = 0.133), narrower 2D band (FWHM = 70 cm⁻¹), and higher crystallinity. XPS analysis shows a nitrogen content of 12.22 at% with a high fraction of quaternary N (32.6 %), achieved without detectable metal carbide impurities. Mechanistic analysis suggests that the CN-rich plasma environment promotes polymerization of nitrogen-containing oligomers (e.g., CN·, C₆H₅·) into ordered graphene frameworks, providing a controllable pathway for tailoring both the structural and chemical properties of NG. Additional precursor tests (σ-bonded aliphatic, π-bonded aromatic, and extended conjugated molecules) further confirm the generality of this CN-driven mechanism. This work establishes a scalable, low-temperature, in-liquid plasma strategy for producing high-purity, nitrogen-rich graphene with tunable functionalities.