Gasidit Panomsuwan

Nitrogen-Doped Carbon Nanoparticle–Carbon Nanofiber Composite as an Efficient Metal-Free Cathode Catalyst for Oxygen Reduction Reaction

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.

Fastest Formation Routes of Nanocarbons in Solution Plasma Processes

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 C2 under 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.

Epitaxial growth of (111)-oriented BaTiO3/SrTiO3 perovskite superlattices on Pt(111)/Ti/Al2O3(0001) substrates

Symmetric BaTiO3/SrTiO3 (BTO/STO) superlattices (SLs) were epitaxially grown on Pt(111)/Ti/Al2O3(0001) substrates with various modulation periods (Λu2009=u20094.8u2009−u200948u2009nm) using double ion beam sputter deposition. The BTO/STO SLs exhibit high (111) orientation with two in-plane orientation variants related by a 180° rotation along the [111]Pt axis. The BTO layer is under an in-plane compressive state, whereas the STO layer is under an in-plane tensile state due to the effect of lattice mismatch. A remarkable enhancement of dielectric constant is observed for the SL with relatively small modulation period, which is attributed to both the interlayer biaxial strain effect and the Maxwell-Wagner effect.

Synthesis of graphitic-N and amino-N in nitrogen-doped carbon via a solution plasma process and exploration of their synergic effect for advanced oxygen reduction reaction

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.

Fe–N-doped carbon-based composite as an efficient and durable electrocatalyst for the oxygen reduction reaction

We herein report the preparation of an Fe–N-doped carbon nanoparticle–carbon nanofiber (Fe–N-CNP–CNF) composite using a solution plasma process followed by heat treatment. The resulting Fe–N-CNP–CNF exhibits excellent catalytic activity, durability, and methanol tolerance for the oxygen reduction reaction (ORR) in an alkaline solution. The enhanced ORR activity of Fe–N-CNP–CNF can reasonably be attributed to the synergistic contributions provided by a high degree of graphitization of CNF, meso/macroporosity of CNP, presence of catalytically active sites for ORR (i.e., graphitic N and Fe–N bond), and existence of carbon-encapsulated Fe/Fe3C particles.

Synthesis of Polybenzoxazine and Nano-Barium Titanate for a Novel Composite

Polymer-ceramic composites are suitable materials for low temperature fabrication of embedded capacitor technology. Dielectric properties of composites can be improved by adding amount of high dielectric constant ceramic powders (i.e. barium titanate). In this study, the composites with 0-3 connectivity were fabricated from barium titanate (BaTiO3) ceramic powders and polybenzoxazine as a polymer matrix. It was found that the dielectric constants of composites at frequency range of 1 kHz -10 MHz increase with increasing the amount of BaTiO3, and shows low frequency dependence. By adding 70wt% of BaTiO3, the dielectric constant at 10 MHz significantly increased from 3.56 of pure polybenzoxazine to 13.2 at room temperature. Dielectric losses of these composites are less than 0.016. Subsequently, Yamadas model with a shape parameter about 5.2 was proposed to describe the dielectric behavior of BaTiO3/polybenzoxazine composites.

Differences in intermediate structures and electronic states associated with oxygen adsorption onto Pt, Cu, and Au clusters as oxygen reduction catalysts

We used ab initio molecular orbital (MO) calculations to study the differences in the intermediate structures and the electronic states involved in the adsorption of O2 onto 13-atom metal clusters of Pt, Cu, and Au. Additionally, the conditions required for the electrocatalytic oxygen reduction reaction (ORR) on the Pt, Cu, and Au clusters were investigated and discussed. The intermediates involved in O2 adsorption onto Pt, Cu, and Au were found to be (Pt–O)–(Pt–O), Cu–O, and Au–O2, respectively. The differences in the O2 adsorption intermediates is explained on the basis of our analysis of the projected density of state (PDOS) area of the new MOs produced from a mixture of the 2pπ * orbitals of O2 and the d orbitals of the metal clusters. The formation of the (Pt–O)–(Pt–O) intermediate after the adsorption of O2 onto the Pt cluster is attributed to the emergence of an antibonding orbital above the Fermi level. Thus, this electronic state can lead to the decomposition and desorption of O2 molecules, thereby promoting the high-activity level of ORR. For the Cu cluster, a new antibonding orbital was observed below the Fermi level. Moreover, the Cu cluster surface can only promote O2 decomposition and not O2 desorption due to the formation of copper oxides. For the Au cluster, no new MOs related to 2pπ * orbitals of O2 appeared because O2 was molecularly adsorbed, implying that the Au cluster is an inefficient ORR catalyst.

X-ray analysis of strain distribution in two-step grown epitaxial SrTiO3 thin films

Epitaxial SrTiO3 (STO) thin films were grown on (001)-oriented LaAlO3 (LAO) substrates using a two-step growth method by ion beam sputter deposition. An STO buffer layer was initially grown on the LAO substrate at a low temperature of 150u2009°C prior to growing the STO main layer at 750u2009°C. The thickness of the STO buffer layer was varied at 3, 6, and 10u2009nm, while the total film thickness was kept constant at approximately 110u2009nm. According to x-ray structural analysis, we show that the STO buffer layer plays an essential role in controlling the strain in the STO layer grown subsequently. It is found that the strains in the STO films are more relaxed with an increase in buffer layer thickness. Moreover, the strain distribution in two-step grown STO films becomes more homogeneous across the film thickness when compared to that in directly grown STO film.

Recycling Waste Soot from Merchant Ships to Produce Anode Materials for Rechargeable Lithium-Ion Batteries

In this study, the waste soot generated by ships was recycled to produce an active material for use in lithium-ion batteries (LIBs). Soot collected from a ship was graphitized by a heat treatment process and used as an anode active material. It was confirmed that the graphitized soot was converted into a highly crystalline graphite, and was found to form carbon nano-onions with an average diameter of 70u2009nm. The graphitized soot showed a high discharge capacity and an excellent cycle life, with a reversible capacity of 260 mAhg−1 even after 150 cycles at a rate of 1u2009C. This study demonstrates that the annealed soot with a unique graphitic multilayer structure has an electrochemical performance that renders it suitable as a candidate for the production of low-cost anode materials for use in LIBs.

Influence of hydrothermal and calcination process on metakaolin from natural clay

In this study, metakaolin was synthesized from natural clay from Lampang province via hydrothermal and calcination process. The hydrothermal process was studied at different temperature from 160 °C, 180 °C and 200 °C for 4, 8 and 12 hours. The calcination process was studied at different temperature from 500 to 900 °C for 2 hours. Regarding the characterization, physical morphology of resulting products was observed by scanning electron microscope showing that the surface of resulting product was enhanced its surface area with more roughness when the temperature was increased. Moreover, FT-IR spectroscopy was applied for the chemical structure analysis indicating that Lampang clay can be transformed into metakaolin using hydrothermal at 200 °C for 8 hours followed by the calcination at 800 °C and 900 °C as well as through the most condition for this studied. The improvement of the surface area of metakaolin leads to high metal dispersion for catalytic activity of the catalyst.In this study, metakaolin was synthesized from natural clay from Lampang province via hydrothermal and calcination process. The hydrothermal process was studied at different temperature from 160 °C, 180 °C and 200 °C for 4, 8 and 12 hours. The calcination process was studied at different temperature from 500 to 900 °C for 2 hours. Regarding the characterization, physical morphology of resulting products was observed by scanning electron microscope showing that the surface of resulting product was enhanced its surface area with more roughness when the temperature was increased. Moreover, FT-IR spectroscopy was applied for the chemical structure analysis indicating that Lampang clay can be transformed into metakaolin using hydrothermal at 200 °C for 8 hours followed by the calcination at 800 °C and 900 °C as well as through the most condition for this studied. The improvement of the surface area of metakaolin leads to high metal dispersion for catalytic activity of the catalyst.