• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.105-105
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• 2012

We have developed a photoemission-assisted plasma-enhanced chemical vapor deposition (PAPE-CVD) [1,2], in which photoelectrons emitting from the substrate surface irradiated with UV light ($h{\nu}$=7.2 eV) from a Xe excimer lamp are utilized as a trigger for generating DC discharge plasma as depicted in Fig. 1. As a result, photoemission-assisted plasma can appear just above the substrate surface with a limited interval between the substrate and the electrode (~10 mm), enabling us to suppress effectively the unintended deposition of soot on the chamber walls, to increase the deposition rate, and to decrease drastically the electric power consumption. In case of the deposition of DLC gate insulator films for the top-gate graphene channel FET, plasma discharge power is reduced down to as low as 0.01W, giving rise to decrease significantly the plasma-induced damage on the graphene channel [3]. In addition, DLC thickness can be precisely controlled in an atomic scale and dielectric constant is also changed from low ${\kappa}$ for the passivation layer to high ${\kappa}$ for the gate insulator. On the other hand, negative electron affinity (NEA) of a hydrogen-terminated diamond surface is attractive and of practical importance for PAPECVD, because the diamond surface under PAPE-CVD with H2-diluted (about 1%) CH4 gas is exposed to a lot of hydrogen radicals and therefore can perform as a high-efficiency electron emitter due to NEA. In fact, we observed a large change of discharge current between with and without hydrogen termination. It is noted that photoelectrons are emitted from the SiO2 (350 nm)/Si interface with 7.2-eV UV light, making it possible to grow few-layer graphene on the thick SiO2 surface with no transition layer of amorphous carbon by means of PAPE-CVD without any metal catalyst.

• Journal of the Korea Organic Resources Recycling Association
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• v.23 no.1
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• pp.45-51
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• 2015

In this study, continuous microbial fuel cells (MFCs) were operated using non-precious metal catalysts such as iron(II) phthalocyanine (FePc) and cobalt tetramethoxyphenylporphyrin (CoTMPP)) as alternative cathode catalysts for platinum. To evaluate MFCs performance, operational conditions of organic loading rate (OLR) (0.5~3 g COD/L/d) and hydraulic retention rate (HRT) (0.25~1 day) were changed. Power density of MFCs were determined by cathode electrode performance. The maximum power density was $3.3W/m^3$ with platinum at OLR 3 g COD/L/d. Given each HRTs at 1 g COD/L/d, FePc showed to be a better alternative for platinum than CoTMPP because the power density of MFC with FePc was similar to that of MFC with platinum. CoTMPP catalyst, however, showed the lowest power density due to increase of internal resistance during continuous operation.

• Korean Journal of Materials Research
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• v.21 no.3
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• pp.180-185
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• 2011

This study is aimed to increase the activity of cathodic catalysts for PEMFCs(Polymer Electrolyte Membrane Fuel Cells). we investigated the temperature effect of 20wt% Pt/C catalysts at five different temperatures. The catalysts were synthesized by using chemical reduction method. Before adding the formaldehyde as reducing agent, process was undergone for 2 hours at the room temperature (RT), $40^{\circ}C$, $60^{\circ}C$, $80^{\circ}C$ and $100^{\circ}C$, respectively. The performances of synthesize catalysts are compared. The electrochemical oxygen reduction reaction (ORR) was studied on 20wt% Pt/C catalysts by using a glassy carbon electrode through cyclic voltammetric curves (CV) in a 1M H2SO4 solution. The ORR specific activities of 20wt% Pt/C catalysts increased to give a relative ORR catalytic activity ordering of $80^{\circ}C$ > $100^{\circ}C$ > $60^{\circ}C$ > $40^{\circ}C$ > RT. Electrochemical active surface area (EAS) was calculated with cyclic voltammetry analysis. Prepared Pt/C (at $80^{\circ}C$, $100^{\circ}C$) catalysts has higher ESA than other catalysts. Physical characterization was made by using X-ray diffraction (XRD) and transmission electron microscope (TEM). The TEM images of the carbon supported platinum electrocatalysts ($80^{\circ}C$, $100^{\circ}C$) showed homogenous particle distribution with particle size of about 2~3.5 nm. We found that a higher reaction temperature resulted in more uniform particle distribution than lower reaction temperature and then the XRD results showed that the crystalline structure of the synthesized catalysts are seen FCC structure.

• Korean Journal of Materials Research
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• v.18 no.11
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• pp.583-591
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• 2008

In this study, two series of CNT/$TiO_2$ electrodes were prepared. The decrease of surface area compared with that of the pristine carbon nanotubes (CNTs) indicated the blocking of micropores on the surface of the CNTs; was further supported by scanning electron microscopy (SEM) and field emission SEM (FE-SEM) observations. The X-ray diffraction (XRD) results showed that the CNT/$TiO_2$ composites contained a mix of anatase and rutile forms of $TiO_2$ particles when the precursor was $TiO_2$ powder, whereas when the precursor was Ti ($OC_4H_7$) (TNB), the composites contained only the typical single and clear anatase $TiO_2$ particles. The energy dispersive X-ray spectroscopy (EDX) spectra showed the presence of C, O and Ti peaks for all samples. It was found that catalytic decomposition of methylene blue (MB) solution could be attributed to synthetic effects between the $TiO_2$ photocatalysis and electro-assisted CNTs network, and that photoelectrocatalytic oxidation increased with an increase of CNT composition. It was also found that the photoelectrocatalytic oxidation efficiency for MB is higher than that of photocatalytic oxidation. Moreover, the CNT/$TiO_2$ composites catalyst prepared by the impregnation method demonstrates higher photoelectrocatalytic activity than the mechanical mixture with the same CNT content.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.288-294
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• 2009

Various polymer electrolyte membrane fuel cell (PEMFC) startup procedures were tested to explore possible techniques for reducing performance decay and improving durability during repeated startup-shutdown cycles. The effects of applying a dummy load, which prevents cell reversal by consuming the air at the cathode, on the degradation of a membrane electrode assembly (MEA) were investigated via single cell experiments. The electrochemical results showed that application of a dummy load during the startup procedure significantly reduced the performance decay, the decrease in the electrochemically active surface area (EAS), and the increase in the charge transfer resistance ($R_{ct}$), which resulted in a dramatic improvement in durability. After 1200 startup-shutdown cycles, post-mortem analyses were carried out to investigate the degradation mechanisms via various physicochemical methods including FESEM, an on-line $CO_2$ analysis, EPMA, XRD, FETEM, SAED, FTIR. After 1200 startup-shutdown cycles, severe Pt particle sintering/agglomeration/dissolution and carbon corrosion were observed at the cathode catalyst layer when starting up a PEMFC without a dummy load, which significantly contributed to a loss of Pt surface area, and thus to cell performance degradation. However, applying a dummy load during the startup procedure remarkably mitigated such severe degradations, and should be used to increase the durability of MEAs in PEMFCs. Our results suggest that starting up PEMFCs while applying a dummy load is an effective method for mitigating performance degradation caused by reverse current under a repetition of unprotected startup cycles.

• Journal of the Korean Electrochemical Society
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• v.12 no.4
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• pp.335-341
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• 2009

Organic-inorganic hybrid sol-gel matrices were used as hosts for chloro (5, 10, 15, 20-tetraphenylporphyrinato) cobalt (III) (Co[TPP]Cl), a known ionophore for nitrite. The sol-gel precursor was prepared by the reaction of (3-isocyanopropyl) triethoxysilane with 1,4-butanediol. An appropriate amount of the anion-exchanger, tridodecylmethylammonium chloride (TDMAC) and the plasticizer, tributylphosphate (DBP) were used as membrane additives. On mixing with an acidic catalyst, the sol-state precursors slowly gelled, yielding a membrane in which the active components, Co[TPP]Cl and TDMAC, were encapsulated. The performances of the sol-gel membrane-based electrodes were compared to those of Co[TPP]Cl-based poly(vinyl chloride) (PVC) membrane electrodes. Membranes with a molar ratio of Co[TPP]Cl: TDMAC (1 : 0.1) showed reasonable response slopes toward nitrite. The response slopes were typically 53 mV/decade between $10^{-5.4}$ and $10^{-1.0}\;M$. Selectivities toward nitrite over hydrophilic and small anions such as chloride were somewhat inferior to those observed with PVC-based membranes, but selectivities over lipophilic anions were quite similar. Reduced asymmetry potentials due to protein adsorption were found to occur with the sol-gel matrix relative to PVC-based films when the sensors were employed as a detector in flow-through configuration.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.3
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• pp.27-33
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• 2004

The catalytic effect of waterworks sludge on NOx removal in $BaTiO_3$pellets and sludge pellets combined packed-bed plasma reactor with plate-plate electrode geometry is measured for the various conditions. NOx removal rate is about 90[%] at $BaTiO_3$-sludge combined reactor used fresh sludge. $NO_2$ and $O_3$ as byproducts are significantly generated in only $BaTiO_3$ packed-bed plasma reactor, however, in $BaTiO_3$-sludge combined packed-bed reactor, $NO_2$ and $O_3$ are completely removed while $CO_2$ as by-products are observed from FTIR spectra. $NO_2$ and $O_3$ seem to react with metallic molecules, metal oxide, and organic compounds that are generally chlorophyll included in sludge. NOx removal rate increases with $O_2$ concentration increasing. Removal rates $NO_2$ and $O_3$ are independent of operating time and repetition measurement times.

• Korean Journal of Materials Research
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• v.20 no.5
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• pp.235-240
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• 2010

We investigated the carbon monoxide (CO) gas-sensing properties of nanostructured Al-doped zinc oxide thin films deposited on self-assembled Au nanodots (ZnO/Au thin films). The Al-doped ZnO thin film was deposited onto the structure by rf sputtering, resulting in a gas-sensing element comprising a ZnO-based active layer with an embedded Pt/Ti electrode covered by the self-assembled Au nanodots. Prior to the growth of the active ZnO layer, the Au nanodots were formed via annealing a thin Au layer with a thickness of 2 nm at a moderate temperature of $500^{\circ}C$. It was found that the ZnO/Au nanostructured thin film gas sensors showed a high maximum sensitivity to CO gas at $250^{\circ}C$ and a low CO detection limit of 5 ppm in dry air. Furthermore, the ZnO/Au thin film CO gas sensors exhibited fast response and recovery behaviors. The observed excellent CO gas-sensing properties of the nanostructured ZnO/Au thin films can be ascribed to the Au nanodots, acting as both a nucleation layer for the formation of the ZnO nanostructure and a catalyst in the CO surface reaction. These results suggest that the ZnO thin films deposited on self-assembled Au nanodots are promising for practical high-performance CO gas sensors.

• Korean Journal of Materials Research
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• v.26 no.11
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• pp.649-655
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• 2016

Ni nanoparticles (NPs)-graphitic carbon nanofiber (GCNF) composites were fabricated using an electrospinning method. The amounts of Ni precursor used as catalyst for the catalytic graphitization were controlled at 0, 2, 5, and 8 wt% to improve the photovoltaic performances of the nanoparticles and make them suitable for use as counter electrodes for dye-sensitized solar cells (DSSCs). As a result, Ni NPs-GCNF composites that were fabricated with 8 wt% Ni precursors showed a high circuit voltage (0.73 V), high photocurrent density ($14.26mA/cm^2$), and superb power-conversion efficiency (6.72%) when compared to those characteristics of other samples. These performance improvements can be attributed to the reduced charge transport resistance that results from the synergetic effect of the superior catalytic activity of Ni NPs and the efficient charge transfer due to the formation of GCNF with high electrical conductivity. Thus, Ni NPs-GCNF composites may be used as promising counter electrodes in DSSCs.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.57.2-57.2
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• 2011

Dye-sensitized solar cells (DSSC) have recently been developed as a cost-effective photovoltaic system due to their low-cost materials and facile processing. The production of DSSC involves chemical and thermal processes but no vacuum is involved. Therefore, DSSC can be fabricated without using expensive equipment. The use of dyes and nanocrystalline $TiO_2$ is one of the most promising approaches to realize both high performance and low cost. The efficiency of the DSSC changes consequently in the particle size, morphology, crystallization and surface state of the $TiO_2$. Nanocrystalline $TiO_2$ materials have been widely used as a photo catalyst and an electron collector in DSSC. Front electrode in DSSC are required to have an extremely high porosity and surface area such that the dyes can be sufficiently adsorbed and be electronically interconnected, resulting in the efficient generation of photocurrent within cells. In this study, DSSC were fabricated by an screen printing for the $TiO_2$ thin film. $TiO_2$ nanoparticles characterized by X-ray diffractometer (XRD) and scanning electron microscope (SEM) and scanning auger microscopy (SAM) and zeta potential and electrochemical impedance spectroscopy(EIS).In addition, DSSC module was modeled and simulated using the SILVACO TCAD software program. Improve the efficiency of DSSC, the effect of $TiO_2$ thin film thickness and $TiO_2$ nanoparticle size was investigated by SILVACO TCAD software program.