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.

Direct growth of anticorrosive magnesium hydroxide films containing Mg–Al layered double hydroxide with anion-exchangeability on magnesium alloy were successfully realized by a simple, easy, environmentally friendly, and chemical-free steam coating method. The crystal structures, chemical composition, surface morphologies, and chemical bonding states of the film were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM) measurements. All the films had thicknesses ranging from 2 to 68 μm depending on the preparation conditions. The films had two crystal structures that were composed of crystalline Mg(OH)₂ and carbonate Mg–Al layered double hydroxide (LDH). The corrosion resistant performances of the films in 5 wt% NaCl aqueous solution were investigated by electrochemical measurements. The potentiodynamic polarization curves revealed that the corrosion current density (j_corr) of a sample treated at 433 K for 6 h decreased by more than six orders of magnitude as compared to that of the bare magnesium alloy, indicating that the film had an inhibiting effect on the corrosion reaction. The formation mechanism of the film was also discussed.

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.

Oxygen-containing nanocarbon materials were successfully synthesized from a mixed solvent of benzene (BZ) and 1,4-dioxane (DO) by solution plasma. TEM observation demonstrated that the synthesized carbons had a diameter in the nanoscale range, their size increased with an increase in the DO content. XRD and Raman spectroscopy measurements revealed that the nanocarbon samples had the (002) characteristic plane of the turbostratic carbon phase and structural defect sites. XPS spectra showed that the nanocarbon sample synthesized from BZ100 consisted of hydroxyl/epoxide groups as the main surface functional groups on the sample surface, whereas the main surface functional groups of the nanocarbon samples synthesized from mixed solvents containing BZ and DO changed from hydroxyl/epoxide groups to carboxyl groups. The O content in the samples increased with an increase in the DO volume ratio in the mixed solvent. The electrocatalytic activity of the synthesized nanocarbon samples for the oxygen reduction reaction (ORR) was investigated electrochemically using cyclic voltammograms (CVs) and linear sweep voltammograms (LSVs) in an O₂-saturated 0.1 M KOH aqueous solution. It was found that the addition of DO to the mixed solvent could only influence the current density, whereas no significant change in the onset potential was observed. The order of the current density of the nanocarbon samples for the ORR was as follows: BZ90 + DO10 > BZ100 > BZ70 + DO30 > BZ50 + DO50. The number of electron transfers for the ORR of the nanocarbon samples estimated by Koutechy–Levich (K–L) plots was about three at low potentials, indicating the coexistence of two- and four-electron reduction of O₂. The oxygen-containing functional groups formed on the carbon surface and structural defects seemed to play the key roles in enhancing the electrocatalytic activity for the ORR rather than the total oxygen content in the nanocarbon samples.

A simple, easy, and rapid process of fabricating superhydrophobic surfaces on magnesium alloy AZ31 by a one-step immersion at room temperature was developed. The myristic acid-modified micro-/nanostructured surfaces showed static water contact angles over 150° and water contact angle hysteresis below 10°, thus illustrating superhydrophobic property. The shortest treatment time for obtaining the superhydrophobic surfaces was 30 s. In addition, we demonstrated for the first time that crystalline solid myristic acid could be formed on a Mg alloy using a suitable molar ratio of Ce ions and myristic acid. The contact angle hysteresis was lowered with an increase in the immersion time. Potentiodynamic polarization curve measurements revealed that the corrosion resistance of AZ31 treated by the immersion process improved considerably by the formation of superhydrophobic surfaces. The chemical durability of the superhydrophobic surfaces fabricated on AZ31 was also examined. The static water contact angle values for the superhydrophobic surfaces after immersion in aqueous solutions at pHs 4, 7, and 10 for 12 h were estimated to be 90 ± 2°, 119 ± 2°, and 138 ± 2°, respectively, demonstrating that their chemical durability in a basic solution was high.