The solution plasma process (SPP), known as non-equilibrium cold plasma at atmospheric pressure and room temperature, was used to investigate the synthesis of nitrogen-carbon nasnosheets (NCNs). To verify the effect of elementary composition and structure of N-methyl-2-pyrrolidone (NMP), various precursors were used in the SPP to synthesize NCNs via the bottom-up synthesis method for the first time. The NCNs were analyzed by transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Among the various precursors, SPP of 2-pyrrolidone was demonstrated to facilitate the formation of highly ordered NCNs. On the other hand, the SPP with cyclopentanone, cyclohexanone and pyrrole did not lead to the formation of carbon nanosheets. The results of this study would uncover new parameter fields for the growth of heteroatom-carbon nanosheets using this synthesis system. In addition, the study is expected to contribute toward research in improving the large-area growth and quality of two-dimensional nanostructures, such as heteroatom-carbon nanosheets or graphene, for various applications in other synthesis methods.Among various carbon nanomaterials, two-dimensional (2D) carbon allotropes such as carbon nanosheets (CNs), which are composed of few-to multi-layer graphene sheets 1, 2 , have emerged as a promising material for the development of lithium-ion batteries 3 , supercapacitors 4 , organic solar cells 5 , sensitive gas-detection materials 6 , field emission materials 7 , carbon dioxide adsorbents 8 , and fuel cells 9 .The introduction of heteroatoms (e.g., nitrogen or boron) into CNs, which do not exhibit a band gap by themselves, has been important for tailoring their electronic properties and chemical reactivity by opening the band gap and modulating conducting types 10-14 . In particular, nitrogen has attracted much attention as the most common dopant element because it is similar in size to carbon and contains five valence bonds with carbon atoms [15][16][17] . Therefore, it can potentially be used for various applications [18][19][20] .Recently, the solution plasma process (SPP), known as non-equilibrium cold plasma at atmospheric pressure and room temperature 21 , was used to synthesize CNs via the bottom-up synthesis method for the first time 22 . Nitrogen-carbon nasnosheets (NCNs), composed of multi-layer graphene (MLG) with turbostratic stacking, were synthesized by the SPP at a high-repetition frequency with N-methyl-2-pyrrolidone (NMP). The findings demonstrated the advantages of the SPP, such as a short synthesis time, simple experimental apparatus, no impurity issues, and the ability to operate at room temperature, when compared with nanosheets prepared by conventional methods 22,23 . Before the synthesis of NCNs, various organic precursor solutions have been used in the SPP to produce carbon nanomaterials for use in carbon nanomaterial-based electrocatalysts such as fuel cells and lithium-air batteries [24][25][26][27] . Although these syntheses were under the same or simi...

Heteroatom-carbon nanosheets, composed of multi-layer graphene with turbostratic stacking, were successfully synthesized through a solution plasma processing (SPP) with N-methyl-2-pyrrolidone at room temperature and an atmospheric pressure.

Nitrogen-containing carbon nanoparticles were synthesized in aniline by solution plasma with high-repetition frequency discharges. We developed a bipolar pulsed power supply that can apply high-repetition frequencies ranging from 25 to 200 kHz. By utilizing high-repetition frequencies, conductive carbons were directly synthesized. The crystallinity was increased and H/C ratio of carbon was decreased. Furthermore, nitrogen atoms were simultaneously embedded in the carbon matrix. Due to the presence of nitrogen atoms, the conductivity and electrocatalytic activity of the samples were remarkably improved compared to that of a pure carbon matrix synthesized from a benzene precursor.

Heterocarbon nanosheets incorporating iron phthalocyanine (FP-NCNs-SP) have been successfully synthesized by a facile one-pot solution plasma process at high repetition frequency. It was found that the Fe-N4 catalytic active sites could be preserved on the FP-NCNs-SP without degradation. The FP-NCNs-SP also possessed large surface area, good conductivity and high degree of graphitization. Electrochemical evaluations demonstrated that NCNs-SP had excellent electrocatalytic activity and selectivity toward oxygen reduction reaction (ORR) in alkaline medium through a direct four-electron pathway. Although the significant improvement in ORR activity was clearly observed in acidic medium, it was much poorer than in alkaline medium. We believe that the results presented in this work will shed light on the advanced synthesis and design of ORR electrocatalysts at room temperature with an abundance of catalytically active sites and high ORR performance.