Fluorine-doped carbon nanoparticles (FCNPs) were synthesized via a simple one-step solution plasma process for the first time. This synthesis strategy can be achieved at relatively low temperature and atmospheric pressure without the involvement of a metal catalyst. A mixture of toluene (C₆H₅CH₃) and trifluorotoluene (C₆H₅CF₃) was used as a precursor for the synthesis. The fluorine doping content can be varied from 0.95 to 4.52 at%, depending on the precursor mixing ratio. The structural analyses reveal that FCNPs mainly exhibit a disordered amorphous structure. The incorporation of fluorine atoms results in the creation of more defect sites and disordered structure in the carbon particles. The electrocatalytic activity toward the oxygen reduction reaction (ORR) of FCNPs in an alkaline solution shows a significant improvement with increasing fluorine doping content, as reflected in an increased limiting current density and a positively shifted onset potential. In association with X-ray photoelectron spectroscopy (XPS) analysis, an improved ORR activity is possibly attributed to the intercalation of ionic C–F and semi-ionic C–F bonds in the carbon structure. In addition, FCNPs possess excellent long-term operation durability and strong tolerance to methanol oxidation compared to those of a commercial Pt-based catalyst. Our results from this study not only confirm the applicability of the solution plasma process to the synthesis of FCNPs with a controllable fluorine doping level but also provide detailed information of FCNPs as potential alternative ORR catalysts for the electrocatalysis research.

We present an alternative way to fabricate a N-doped carbon matrix via a room temperature solution plasma process. The type of C–N bonding states was controlled by choosing the structure of the original precursor and additive. In this research, pyridine and acrylonitrile were employed as the heterocyclic and linear structure precursor respectively. A small amount of anthracene (7 mM) was introduced as an additive to further promote the graphitic structure in the carbon matrix. The effects of the structure of the CN precursor on the chemical bonding states and electrocatalytic activities were investigated. The most pronounced peak was pyridinic-N when pyridine was applied as the precursor, whereas the dominant peak shifted to amino-N when the precursor changed to acrylonitrile. Furthermore, graphitic-N increased 30–40% when anthracene was added to the original precursors. From the results of electrochemical measurements, the current density was proportional to the content of graphitic-N, while a higher percentage of amino-N shifted the ORR onset potential to more positive values. N-doped carbon with the highest graphitic-N content showed the highest electron transfer number of 3.7 and the lowest peroxide yield of 30%. In contrast, N-doped carbon consisting of dominant pyridinic-N resulted in the lowest current density, ORR onset and peak potentials. The results indicated that the presence of graphitic-N encouraged a direct four electron transfer pathway for ORR. Herein, our research showed a room temperature solution method to control the chemical bonding states of nitrogen through designing the original precursors for the first time, as well as reports the synergic effect of amino-N and graphitic-N towards advanced ORR activity.

We report the in situ synthesis of nitrogen-doped carbon nanoparticles (NCNPs) by a solution plasma process without the addition of metal catalysts. Organic liquid mixtures of benzene and pyrazine were used as the precursors for the synthesis. The nitrogen-doping content can be easily controlled by changing the amount of pyrazine in the precursor. The NCNPs synthesized from the solution plasma process exhibit a turbostratic structure with highly uniform nanoscale particles. The nitrogen atoms can be homogeneously incorporated into the entire carbon structure due to the in situ doping during the growth and formation of the carbon particles. The electrochemical activity toward the oxygen reduction reaction (ORR) of the NCNPs in an alkaline medium reveals the improvement in terms of both the onset potential and current density as the nitrogen-doping content increases. The enhanced ORR activity of the NCNPS is mainly attributed to the presence of pyridinic-N and graphitic-N bonding configurations. They also possess long-term durability and excellent tolerance to methanol crossover effects. The results obtained in this study have demonstrated that the solution plasma process has great potential for the synthesis of metal-free nitrogen-doped carbon electrocatalysts for the ORR. We expect that this approach can be extended to the synthesis of other heteroatom-doped carbonaceous materials for a broad range of research applications in energy conversion and storage.

Stable black titania spheres (H-TiO_2−x) were synthesized via a simple green method assisted by water plasma at a low temperature and atmospheric pressure.

Although solution-plasma processing enables room-temperature synthesis of nanocarbons, the underlying mechanisms are not well understood. We investigated the routes of solution-plasma-induced nanocarbon formation from hexane, hexadecane, cyclohexane, and benzene. The synthesis rate from benzene was the highest. However, the nanocarbons from linear molecules were more crystalline than those from ring molecules. Linear molecules decomposed into shorter olefins, whereas ring molecules were reconstructed in the plasma. In the saturated ring molecules, C–H dissociation proceeded, followed by conversion into unsaturated ring molecules. However, unsaturated ring molecules were directly polymerized through cation radicals, such as benzene radical cation, and were converted into two- and three-ring molecules at the plasma–solution interface. The nanocarbons from linear molecules were synthesized in plasma from small molecules such as C₂under heat; the obtained products were the same as those obtained via pyrolysis synthesis. Conversely, the nanocarbons obtained from ring molecules were directly synthesized through an intermediate, such as benzene radical cation, at the interface between plasma and solution, resulting in the same products as those obtained via polymerization. These two different reaction fields provide a reasonable explanation for the fastest synthesis rate observed in the case of benzene.