Metal-free nitrogen-doped carbon materials are currently considered at the forefront of potential alternative cathode catalysts for the oxygen reduction reaction (ORR) in fuel cell technology. ...Despite numerous efforts in this area over the past decade, rational design and development of a new catalyst system based on nitrogen-doped carbon materials via an innovative approach still present intriguing challenges in ORR catalysis research. Herein, a new kind of nitrogen-doped carbon nanoparticle–carbon nanofiber (NCNP–CNF) composite with highly efficient and stable ORR catalytic activity has been developed via a new approach assisted by a solution plasma process. The integration of NCNPs and CNFs by the solution plasma process can lead to a unique morphological feature and modify physicochemical properties. The NCNP–CNF composite exhibits a significantly enhanced ORR activity through a dominant four-electron pathway in an alkaline solution. The enhancement in ORR activity of NCNP–CNF composite can be attributed to the synergistic effects of good electron transport from highly graphitized CNFs as well as abundance of exposed catalytic sites and meso/macroporosity from NCNPs. More importantly, NCNP–CNF composite reveals excellent long-term durability and high tolerance to methanol crossover compared with those of a commercial 20 wt % supported on Vulcan XC-72. We expect that NCNP–CNF composite prepared by this synthetic approach can be a promising metal-free cathode catalyst candidate for ORR in fuel cells and metal−air batteries.
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IJS, KILJ, NUK, PNG, UL, UM
Fluorine-doped carbon nanoparticles (FCNPs) were synthesized viaa 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 (C sub(6)H sub(5)CH sub(3)) and trifluorotoluene (C sub(6)H sub(5)CF sub(3)) 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.
Metal-free nitrogen-doped carbon nanoparticles (NCNPs) have been synthesized via a solution plasma process with the potential to achieve uniformly distributed nitrogen atoms. A set of cyano-aromatic ...molecules, including benzonitrile, 2-cyanopyridine, and cyanopyrazine, were used as a single-source precursor in the synthesis without the addition of a metal catalyst source. The resultant NCNPs reveal uniformly nanosized particles (20–40 nm) and an interconnected hierarchical pore structure with a high specific surface area (210–250 m2 g−1). The difference in carbon/nitrogen mole ratios of organic precursors gives rise to the variation of nitrogen-doping level in NCNPs from 0.63 to 1.94 atom %. Detailed electrochemical evaluation toward the oxygen reduction reaction (ORR) demonstrates that NCNPs exhibit a significant improvement in terms of both onset potential and current density under alkaline and acidic conditions. The predominant distribution of graphitic-N and pyridinic-N sites on NCNPs plays an essential role in enhancing the ORR activity and the selectivity toward a four-electron reduction pathway. More importantly, NCNPs possess excellent robust long-term durability and strong methanol tolerance compared with those of a commercial Pt/carbon catalyst.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Abstract
Cathode materials are essential for enhancing electrocatalytic activity in energy-conversion devices. Carbon is one of the most suitable cathodic materials for Li–O
2
batteries owing to its ...chemical and thermal stability. Carbon materials synthesized from tributyl borate (TBB) using a nonthermal solution plasma method were characterized using x‐ray diffraction, Raman, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy, and x-ray photoelectron spectroscopy and were evaluated as additive materials for cathodes in a Li–O
2
battery. Two separate carbon materials were formed at the same time, a carbon dispersed in solution and a carbon precipitate at the bottom of the reactor, which had amorphous and graphite-like structures, respectively. The amorphous carbon contained boron and tungsten carbide, and the graphite-like carbon had more defects and electronic conductivity. The crystallinity and density of defects in the graphite-like carbon could be tuned by changing the SP operating frequency. The Li–O
2
battery with the amorphous carbon containing boron and tungsten carbide was found to have a high capacity, while the one with the graphite-like carbon showed an affinity for the formation of Li
2
O
2
, which is the desired discharge product, and exhibited high cycling performance.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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•Composite films were formed on non-combustible magnesium alloy by steam coating.•The film consists of mixed phases composed mainly of Mg(OH)2 and Mg–Al LDH.•Corrosion resistance of ...the film were investigated by electrochemical measurements.
Films of the Mg(OH)2/Mg–Al layered double hydroxide composite were formed on the combustion-resistant magnesium alloy AMCa602 by steam coating and characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy. The corrosion-resistance performances of the films in a 5wt% NaCl solution were investigated using electrochemical measurements. The corrosion current density of the sample that was steam-coated at 433K for 6h using the aqueous solution containing 200mM Al(NO3)3 decreased significantly more than that of the bare AMCa602. The correlations between the Mg–Al LDH content in the films, Al(NO3)3 concentration in the aqueous solutions, and corrosion current densities were investigated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Nitrogen-doped carbon nanoparticles were synthesized via a solution plasma process, with acrylonitrile as a single-source precursor, followed by a post-thermal annealing process. The nitrogen-bonding ...states can be tuned by varying the annealing temperature. The best electrocatalytic activity for oxygen reduction reaction (ORR) in terms of both onset potential and limiting current density can be achieved for the catalyst annealed at an optimal temperature of 800 °C because of the high content of graphitic-N catalytic sites and a large specific surface area.
A super-hydrophobic film was successfully deposited on magnesium alloy AZ31 by the microwave plasma-enhanced chemical vapor deposition (MPECVD) process. The film surface showed a static water contact ...angle of more than 150°. The hydrophobicity and root mean square roughness of the film surface increased with an increase in deposition time. The anticorrosion resistance of the deposited film was estimated by electrochemical impedance spectroscopy (EIS) measurements. The EIS measurements and appropriate equivalent circuit models revealed that the super-hydrophobic film considerably improved the anticorrosion resistant performance of magnesium alloy AZ31. The anticorrosion mechanism of the super-hydrophobic film was also considered. Moreover, the chemical stability of the super-hydrophobic film in acidic, neutral, and alkaline aqueous solutions was investigated. The super-hydrophobic film showed high chemical stability in acidic and neutral aqueous solutions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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 mu m depending on the preparation conditions. The films had two crystal structures that were composed of crystalline Mg(OH) sub(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 sub(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.
The synthesis of boron-doped carbon nanoparticles (BCNP) has been achieved through a solution plasma process without the addition of a metal catalyst source using a mixture of benzene and triphenyl ...borate as precursor. The electrocatalytic activity toward the oxygen reduction reaction (ORR) of BCNP can be improved in terms of onset potential and current density compared to that of undoped carbon nanoparticles in alkaline solution. Moreover, BCNP possesses superior long-term durability and tolerance to methanol oxidation in the ORR.
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•Boron-doped carbon nanoparticles (BCNP) were synthesized by solution plasma process.•Boron doping can improve the oxygen reduction reaction (ORR) activity in alkaline solution.•The ORR catalyzed on BCNP proceeds through two-step consecutive two-electron pathway.•BCNP exhibits better durability in comparison with a commercial Pt/carbon catalyst.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Selective N moieties in N-doped carbon catalysts were successfully controlled by a room temperature plasma process, where its ORR catalytic activity was found to be related to Lewis Basicity of ...catalysts.
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•Tailored 4 types of nitrogen bonding states in N-doped carbon by plasma synthesis.•Correlated the Lewis basicity of N-doped carbon catatlysts to their ORR activities.•Amino-N showed the superior Lewis basicity and ORR activity.
The ORR electrocatalytic activity of nitrogen-doped carbon (N-doped carbon) is highly related to the type of nitrogen bondings, which is originated to the charge transfer between carbon and nitrogen. Based on Lewis theory of acid-base reactions, N-doped carbon can be defined as a Lewis base catalyst. The lone pair of electrons on the nitrogen atom mainly contributed to its reactivity, or in other terms, Lewis basicity. Herein, we fabricated selective amino-N, pyrrolic-N, nitrile-N, and oxide-N in N-doped carbon systematically, as well as compared their electrocatalytic activities and Lewis basicities for the first time. Based on the molecular structure of four starting precursors, aniline (C6H5NH2), pyrrole (C4H5N), benzonitrile (C5H7N), and nitrobenzene (C6H5NO2) were successfully formed as selective amino-N, pyrrolic-N, nitrile-N and oxide-N, respectively, via a room temperature plasma synthesis process. From the electrochemical performance, N-doped carbon catalyst with highly selective amino-N demonstrated comparatively higher ORR activity in terms of ORR onset potential and current density. Also, we confirmed the correlation between the ORR activity and Lewis basicity of various N moieties. Based on the electronic structural properties, amino-N with the most superior ORR activity also exhibited the highest basic strength among the studied CN bonding structure. This study provided the relationship among the structural properties, Lewis basicity, and electrocatalytic activity of selective N-doped carbon.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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