• Journal of the Korean Ceramic Society
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• v.53 no.5
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• pp.511-520
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• 2016

Electrolyte-supported symmetric Ni-YSZ cermet electrodes of ca. $23{\mu}m$ were prepared by screenprinting and the impedance was measured as a function of humidity from 2% to 90% balanced in $H_2$ at a total flow rate of 50 sccm. The Ni felt current collector of 1 mm thickness exhibited a Gerischer-like gas concentration impedance in the low frequency range, which was similarly observed in the cermet-supported solid oxide cells, while the Pt paste collector exhibited only electrochemical polarization. The electrochemical polarization of both samples was modeled by a non-ideal diffusion-reaction transmission line model including CPEs with ${\alpha}$= 0.5. In the case of the Pt paste collector, all the Bisquert parameters exhibited humidity dependence to the -1/2 power, supporting a non-faradaic chemical reaction mechanism at three phase boundaries. Consequently, the surface diffusivity and reaction rate increased linearly with humidity. Less pronounced humidity dependence and somewhat lower utilization length with an Ni felt collector can be attributed to the diffusion-limited gas flow through the collector.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.358-359
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• 2006

Ru-C nano-composite films were prepared by MOCVD, and their microstructures and their electrode properties for oxygen gas sensors were investigated. Deposited films contained Ru particles of 5-20 nm in diameter dispersed in amorphous C matrix. The AC conductivities associating to the interface charge transfer between Ru-C composite electrode and YSZ electrolyte were 100-1000 times higher than that of conventional paste-Pt electrodes. The emf values of the oxygen gas concentration cell constructed from the nano-composite electrodes and YSZ electrolyte showed the Nernstian theoretical values at low temperatures around 500 K. The response time of the concentration cell was 900 s at 500 K.

• Corrosion Science and Technology
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• v.17 no.5
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• pp.249-256
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• 2018

Metallic structures in the oil and gas production undergo severe degradation due to sweet and sour corrosion caused by the presence of $CO_2$ and $H_2S$ in the fluid environment. The corrosion behavior of 304 austenitic stainless was investigated in the presence of varying concentrations of $CO_2$ or $H_2S$ and $CO_2+H_2S$ to understand the effect of the parameters either individually or in combination. Potentiodynamic polarization study revealed that a small amount of $CO_2$ aided in the formation of calcareous deposit of protective layer on passive film of 304 steel, while increase in $CO_2$ concentration ruptured the layer resulting in sweet corrosion. The presence of $S^{2-}$ damaged the passive and protective layer of the steel and higher levels increased the degradation rate. Electrochemical impedance studies revealed lower polarization resistance and impedance at higher concentration of $CO_2$ or $H_2S$, supporting the outcomes of polarization study. XRD analysis revealed different types of iron carbides and iron sulphides corresponding to sweet and sour corrosion as the corrosion products, respectively. SEM analysis revealed the presence of uniform, localized and sulphide cracking in sour corrosion and general corrosion with protective carbide layer amid for sweet corrosion.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.461-461
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• 2010

For a low dielectric constant inter-metal dielectric application, the low-k SiCOH film with a dielectric constant of 2.8-3.2 has been deposited by plasma-enhanced chemical vapor deposition with decamethylcyclopentasiloxane, cyclohexane, and helium which is carrier gas. In this work, we investigated chemical deposition rate, dielectric constant, characterization of plasma polymer films according to temperature(25C-200C) of substrate and change of component concentration. We measured impedance by using V-I prove during process. From experimental result, deposition rate decrease with increasing temperature. Through real time impedance analysis of chamber, we find corelation between film thickness and impedance by assuming equivalent circuit.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.192-193
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• 2005

Magnesium thin films were prepared on cold-rolled steel substrates by RF(Radio Frequency) magnetron sputtering technique.$^{1)}$ The crystal orientation and monitoring of the deposited films were investigated by using XRD(X-ray Diffraction) and EIS(Electrochemical Impedance Spectroscopy), respectively. The corrosion rates of Mg thin films deposited with different argon gas pressure and substrate bias voltage were monitored by AC impedance method under a cyclic wet-dry condition, which was conducted by exposure to alternate conditions of 1h immersion in 3%NaCl solution and 5h drying at 60% RH and 25$^{\circ}C$. The result of corrosion rate of Mg thin films deposited at various Ar gas pressures and substrate bias voltage under wet-dry cyclic exposure in chloride-containing solutions was showed the following conclusions. At the region I during the onset of the wet cycle, corrosion rate showed relatively low value. The increase in the Corrosion rate of region II is due to the increase in the chloride concentration. Corrosion rate of region III during the onset of the cycle zero and salt crystals remain on the metal surface.$^{2)}$

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.184-187
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• 2007

Hydrogen could be produced from any substance containing hydrogen atoms, such as water, hydrocarbon (HC) fuels, acids or bases. Hydrocarbon fuels couold be converted to hydrogen-rich gas through reforming process for hydrogen production. Even though fuel cell have high efficiency with pure hydrogen from gas tank, it is more beneficial to generate hydrogen from city gas (mainly methane) in residential application such as domestic or office environments. Thus hydrogen is generated by reforming process using hydrocarbon. Unfortunately, the reforming process for hydrogen production is accompanied with unavoidable impurities. Impurities such as CO, $CO_2$, $H_2S$, $NH_3$, and $CH_4$ in hydrogen could cause negative effects on fuel cell performance. Those effects are kinetic losses due to poisoning of electrode catalysts, ohmic losses due to proton conductivity reduction including membrane and catalyst ionomer layers, and mass transport losses due to degrading catalyst layer structure and hydrophobic property. Hydrogen produced from reformer eventually contains around 73% of $H_2$, 20% or less of $CO_2$, 5.8% of less of $N_2$, or 2% less of $CH_4$, and 10ppm or less of CO. Most impurities are removed using pressure swing adsorption (PSA) process to get high purity hydrogen. However, high purity hydrogen production requires high operation cost of reforming process. The effect of carbon dioxide on fuel cell performance was investigated in this experiment. The performance of PEM fuel cell was investigated using current vs. potential experiment, long run (10 hr) test, and electrochemical impedance measurement when the concentrations of carbon dioxide were 10%, 20% and 30%. Also, the concentration of impurity supplied to the fuel cell was verified by gas chromatography (GC).

• The Korean Journal of Ceramics
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• v.4 no.2
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• pp.114-121
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• 1998

Using Hebb-Wagner's asymmetric cell, partial conductivities of holes and electrons in yttria stabilized zirconia doped with 10 mol% TiO2 have been estimated by a dc polarization measurement. The current interrruption method and ac impedance measurements have been also made to evaluate the ionic conductivity and to examine the consistency of the partial conductivities. Partial conductivities of electrons(σn) and holes (σp) were found to be pro-peortional to -1/4 and 1/4 power of partial pressure of oxygen gas, respectively, except for σn at reducing conditions. In comparison with 5 mol% doped YSZ, σn was found to increase with the increase of TiO2 concentration, but σp stayed at almost a constant value.

• Transactions of the Korean hydrogen and new energy society
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• v.18 no.4
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• pp.432-438
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• 2007

The reforming process for hydrogen production generates some impurities. Impurities in hydrogen such as $CO_2$, CO, $H_2S$, $NH_3$ affect fuel cell performance. It is well known that CO generated by the reforming process may negatively affect performance of cell, cause damage on catalysts resulting performance degradation. Hydrogen produced by reforming process includes about 2% methane. The presence of methane up to 10% is reported negligible degradation in cell performance. However, methane more than 10% in hydrogen stream had not been researched. The concentration of impurity supplied to the fuel cell was verified by gas chromatography(GC). In this study, the influence of $CH_4$ on performance of PEM fuel cell was investigated by means of current vs. potential experiment, long run(10 hr) test and electrochemical impedance measurement when the concentrations of impurities were 10%, 20% and 30%.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.4
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• pp.291-298
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• 2008

Carbon monoxide(CO) is one of the contamination source in reformed hydrogen fuel with an influence on performance of polymer electrolyte membrane fuel cell(PEMFC). The studies of CO injection presented here give information about poisoning and recovery processes. The aim of this research is to investigate cell performance decline due to carbon monoxide impurity in hydrogen. Performance of PEM fuel cell was investigated using current vs. potential experiment, long time(10 hours) test, cyclic feeding test and electrochemical impedance spectra. The concentrations of carbon monoxide were changed up to 10 ppm. Performance degradation due to carbon monoxide contamination in anode fuel was observed at high concentration of carbon monoxide. The CO gas showed influence on the charge transfer reaction. The performance recovery was confirmed in long time test when pure hydrogen was provided for 1 hour after carbon monoxide had been supplied. The result of this study could be used as a basis of various reformation process design and fuel quality determination.

• Journal of the Korean Electrochemical Society
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• v.10 no.4
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• pp.301-305
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• 2007

The performance of polymer electrolyte membrane fuel cell could be decreased due to coolant leaked from connection part. Micro pump was used to put small amount of coolant and investigate the effect on fuel cell. The stoichiometric ratio of hydrogen/air was 1.5/2.0, both side of gas was fully humidified, and current density of $400mA/cm^2$ was used as standard condition in this experiment. Constant current method was used to check performance recovery from coolant effect in 3 cell stack. The performance was recovered when coolant was injected in cathode side. On the other hand, the performance was not recovered when coolant was injected in anode side. Ethylene glycol could be converted to CO in oxidation process and cause poisoning effect on platinum catalyst or be adhered on GDL and cause gas diffusion block effect resulting performance decrease. Water with nitrogen gas was supplied in anode side to check performance recovery. Polarization curve, cyclic voltammetry, electrochemical impedance spectroscopy was used to check performance, and gas chromatography was used to check coolant concentration. Constant current method was not enough in full recovery of performance. However, water injection method was proved good method in full recovery of performance.