• Title, Summary, Keyword: Polarization resistance

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Fabrication Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF)/Ce0.9Gd0.1O2−δ (GDC) and La0.6Ba0.4Co0.2Fe0.8O3−δ (LBCF)/Ce0.9Gd0.1O2−δ (GDC) Composite Cathodes for Intermediate Temperature Solid Oxide Fuel Cells (중저온 SOFC용 Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF)/Ce0.9Gd0.1O2−δ (GDC) 및 La0.6Ba0.4Co0.2Fe0.8O3−δ (LBCF)/Ce0.9Gd0.1O2−δ (GDC) 복합체 양극 제조)

  • Lee, Seung-Hun;Yoon, Song-Seol;Cha, Young-Chul;Lee, Jun;Hwang, Hae-Jin;Moon, Ji-Woong
    • Journal of the Korean Ceramic Society
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    • v.44 no.12
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    • pp.740-746
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    • 2007
  • The potential candidates for IT-SOFCs cathode materials, $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$ (BSCF) and $La_{0.6}Ba_{0.4}Co_{0.2}Fe_{0.8}O_{3-{\delta}}$ (LBCF) powders, were synthesized by a EDTA-citrate combined method from $Sr(NO_3)_2$, $Ba(NO_3)_2$, $La(NO_3)_3{\cdot}6H_2O$, $Co(NO_3)_2{\cdot}6H_2O$, $Fe(NO_3)_3{\cdot}9H_2O$, citric acid and $EDTA-NH_3$. The cathode performance of symmetrical electrochemical cells consisting of BSCF-GDC or LBCF-GDC composite electrodes and a GDC electrolyte was investigated using by AC impedance spectroscopy at the temperature range of 500 to $700^{\circ}C$. It was found that a single phase perovskite could be successfully synthesized when the precursor is heated at $850^{\circ}C$ for 2 h. Due to thermal expansion mismatch between BSCF and GDC, the composite cathodes with lower GDC content than 45 wt% were peeled off from the GDC electrolyte and their electrode polarization resistance was estimated to be high. The thermal expansion coefficient of BSCF-GDC composites was decreased with increasing the GDC content and the electrode peeling off did not occur in BSCF-45 and 55 wt% GDC composites. BSCF-45 wt% GDC composite electrode showed the lowest area specific resistances (ASR) of 0.15 and $0.04{\Omega}{\cdot}cm^2$ at 600 and $700^{\circ}C$, respectively. On the other hand, LBCF-GDC composite cathodes showed higher ASR than the BSCF-45 and 55 wt% GDC and their cathode performance were decreased with the GDC content.

Synthesis and Electrochemical Properties of (La0.6Sr0.4)(Co0.2Fe0.8)O3 cathode for SOFC on pH Control Using Modified Oxalate Method (Modified Oxalate Method 의해 합성한 SOFC용(La0.6Sr0.4)(Co0.2Fe0.8)O3 Cathode의 pH 변화에 따른 특성)

  • Lee, Mi-Jai;Choi, Byung-Hyun;Kim, Sei-Ki;Park, Sang-Sun;Lee, Kyung-Hee
    • Journal of the Korean Electrochemical Society
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    • v.10 no.4
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    • pp.288-294
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    • 2007
  • The LSCF cathode far Solid Oxide Fuel Cell was investigated to develop high performance unit cell at intermediate temperature by modified oxalate method with different electrolytes and different pH. The LSCF powders employed La, Sr, Co and Fe oxides, oxalic acid, ethanol and $NH_4OH$ solution were synthesized with pH controlled as 2, 6, 7, 8, 9 and 10 at $80^{\circ}C$ Single crystalline phase was obtained from pH $2{\sim}9$. on the other hand, $La_2O_3$ appeared from pH 10. Very fine powder with particle size of 50 nm was obtained at calcination temperature of $800^{\circ}C$ for 4 hours. LSCF cathode synthesized at pH 7 showed the highest electric conductivity in the temperature range of $600^{\circ}C$ to $900^{\circ}C$ its value was 950 S/cm at $900^{\circ}C$ Under same synthesis conditions, polarization resistance of each LSCF cathode was changed with different calcination temperatures. As-prepared powder presented 2.52, 1.54 and $2.58\;{\Omega}$ at $600^{\circ}C$ with ScSZ, 8Y-YSZ and GDC as its electrolyte respectively after calcination at $800^{\circ}C$ for 4 hours.

Effect of the A-site Deficieny of ABO3 type (La0.75Sr0.25)1-xFeO3-δ Used as Cathode Materials for SOFC on the Electrode Properties (고체산화물 연료전지의 공기극용 ABO3구조의 (La0.75Sr0.25)1-xFeO3-δ의 A-site변화에 따른 전극 특성 연구)

  • Park, Ju-Hyun;Lee, Seung-Bok;So, Hui-Jeong;Lim, Tak-Hyoung;Yoon, Soon-Gil;Shin, Dong-Ryul;Song, Rak-Hyun
    • Journal of the Korean Electrochemical Society
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    • v.11 no.2
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    • pp.89-94
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    • 2008
  • We synthesized and investigated $(La_{0.75}Sr_{0.25})_{1-x}FeO_{3-\delta}$ perovskite oxides having different stoichiomety (x = 0, 0.02, 0.04, 0.06, 0.08) as cathode materials. SEM images and XRD patterns reveal that the synthesized powder has uniform size distribution and high degree of crystallinity. The electrochemical performances of the synthesized powders were investigated by AC impedance spectroscopy. Both the electric conductivity and the electrochemical performance showed the highest properties at the stoichiometry x = 0.02. Finally, we concluded that the variation of A-site deficiency results in the variation of the amount of oxygen vacancy and micro structure, which leads to the variation of electric conductivity and polarization resistance.

Effects of alloy elements on electrochemical characteristics improvement of stainless steel in sea water (해수환경하에서 스테인리스강의 전기화학적 특성 개선을 위한 합금원소의 영향)

  • Lee, Jung-Hyung;Choi, Yong-Won;Jang, Seok-Ki;Kim, Seong-Jong
    • Journal of the Korean Society of Marine Engineering
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    • v.38 no.7
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    • pp.890-899
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    • 2014
  • Austenitic stainless steel is widely used in various industries due to its excellent corrosion resistance. However, Cr carbides precipitation along the grain boundaries after heat treatment or welding may develop Cr depleted zone, which acts as a preferential site for intergranular corrosion attack. To resolve this, carbon stabilizing element such as Ti or Nb are added to suppress formation of Cr carbides. However, there are few reports on corrosion characteristics under seawater environment of the stabilized stainless steel. This study investigated the effects of alloying contents on the electrochemical characteristics in seawater of stainless steel containing stabilizing element(Ti and Nb). To achieve this, the changes on the microstructure due to alloying were observed with microscope, and the electrochemical characteristics were determined by measurement of natural potential and potentiodynamic polarization experiments. The microscopic observation revealed that all specimens had inclusions other than the austenite matrix phase due to the addition of alloying elements. Such inclusions are considered to have different electrochemical characteristics from those of the matrix, and thus a clear distinction was found according to the type of stabilizers and the contents. The results of this study suggest that it is important to consider the effects of alloying contents on the electrochemical characteristics in seawater with the addition of Ti or Nb into austenitic stainless steel.

Electrorefining Behavior of Zirconium Scrap with Multiple Cathode in Fluoride-Based Molten Salt (불화물계 용융염을 이용한 지르코늄 스크랩의 다중전극 전해정련 거동)

  • Park, Dong Jae;Kim, Seung Hyun;Park, Kyoung Tae;Mun, Jong Han;Lee, Hyuk Hee;Lee, Jong Hyeon
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.13 no.1
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    • pp.11-19
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    • 2015
  • The production of nuclear fuel cladding tube is expected to increase with the nuclear power plant expansion. Zirconium(Zr) scrap that is generated during manufacturing is also expected to increase. Zr electrorefining experiment was carried out in the fluoride salt of LiF-KF-ZrF4 using multiple electrode for scale up and improving throughput Zr electrorefiner develop-ment. The Zr reduction peak observed at-0.8 V(vs.Ni). Polarization behavior showed that the amount of applied current increases because of decreasing cell resistance as the number of cathode increases. Experimental results showed the highest recovery rate about 98% at lowest current density of 25.64 mA/cm2 using 6 electrodes. XRD and TG analysis result show that pure Zr was recovered 99.92% and ICP analysis shows that lower impurity content than conventional impurity content of the Anode(97.8%). Electrorefining consumes energy about 7.15 kWh/kg less than 39.7% compared to the Kroll process using 6 electrode width of 20 mm and height of 65 mm. Because of increasing cell efficiency and recovery rate, using multiple cathode is determined as an efficient technique for scale up electrorefining Zr scrap.

Morphology Controlled Cathode Catalyst Layer with AAO Template in Polymer Electrolyte Membrane Fuel Cells (AAO를 사용한 고분자전해질 연료전지의 공기극 촉매층 구조 제어)

  • Cho, Yoon-Hwan;Cho, Yong-Hun;Jung, Nam-Gee;Ahn, Min-Jeh;Kang, Yun-Sik;Chung, Dong-Young;Lim, Ju-Wan;Sung, Yung-Eun
    • Journal of the Korean Electrochemical Society
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    • v.15 no.2
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    • pp.109-114
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    • 2012
  • The cathode catalyst layer in polymer electrolyte membrane fuel cells (PEMFCs) was fabricated with anodic aluminum oxide (AAO) template and its structure was characterized with scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis. The SEM analysis showed that the catalyst layer was fabricated the Pt nanowire with uniform shape and size. The BET analysis showed that the volume of pores in range of 20-100 nm was enhanced by AAO template. The electrochemical properties with the membrane electrode assembly (MEA) were evaluated by current-voltage polarization measurements and electrochemical impedance spectroscopy. The results showed that the MEA with AAO template reduced the mass transfer resistance and improved the cell performance by approximately 25% through controlling the structure of catalyst layer.

Effect of Period of Immersion on Corrosion Potential, Anodic Polarization, and Impedance Characteristics of Reinforced Steel in Mortar (W/C: 0.6) (모르타르(W/C:0.6)의 철근의 부식전위와 양극분극 및 임피던스 특성에 미치는 재령 년수)

  • Jeong, Jae-Hyun;Moon, Kyung-Man;Lee, Sung-Yul;Lee, Myeong-Hoon;Baek, Tae-Sil
    • Journal of Ocean Engineering and Technology
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    • v.30 no.4
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    • pp.327-333
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    • 2016
  • Reinforced concrete structures have found wide usage in land and maritime applications. However, the corrosion of reinforced concrete has been recognized as a serious problem from economic and safety standpoints. In previous studies, the corrosion behavior of the inner steel bar embedded in mortar (W/C: 0.4, 0.5) was investigated using electrochemical methods. In this study, multiple mortar test specimens (W/C: 0.6) with six different cover thicknesses were prepared and immersed in flowing seawater for five years. Subsequently, equations related to the cover thickness, period of immersion, and corrosion characteristics of the embedded steel bar were evaluated using electrochemical methods. Prior to immersion, the corrosion potentials indicated an increase with increasing cover thickness, and after five years, all corrosion potentials demonstrated a trend in the positive direction irrespective of the cover thickness. However, the relationships between the corrosion potential and cover thickness were not in complete agreement. Furthermore, after five years, all of the corrosion potentials indicated values that were nobler compared to those obtained prior to immersion, and their corrosion current densities also decreased compared to their values obtained prior to immersion. It was considered that the embedded steel bar was easily corroded because of the aggression of water, dissolved oxygen, and chloride ions; a higher W/C ratio also assisted the corrosion process. The corrosive products deposited on the surface of the steel bar for five years cast a resistance polarizing effect shifting the corrosion potential in the nobler direction. Consequently, it was considered that the W/C ratio of 0.6 showed nearly same results as those of W/C of 0.4 and 0.5. Therefore, the corrosion potential as well as various parameters such as the cover thickness, period of immersion, and W/C ratio must be considered at once for a more accurate evaluation of the corrosion property of reinforced steel exposed to marine environment for a long period.

Photoelectrochemical Properties of Gallium Nitride (GaN) Photoelectrode Using Cobalt-phosphate (Co-pi) as Oxygen Evolution Catalyst (산소발생용 Cobalt-phosphate (Co-pi) 촉매를 이용한 Gallium Nitride (GaN) 광전극의 광전기화학적 특성)

  • Seong, Chaewon;Bae, Hyojung;Burungale, Vishal Vilas;Ha, Jun-Seok
    • Journal of the Microelectronics and Packaging Society
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    • v.27 no.2
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    • pp.33-38
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    • 2020
  • In the photoelectrochemical (PEC) water splitting, GaN is one of the most promising photoanode materials due to high stability in electrolytes and adjustable energy band position. However, the application of GaN is limited because of low efficiency. To improve solar to hydrogen conversion efficiency, we introduce a Cobalt Phosphate (Co-pi) catalyst by photo-electrodeposition. The Co-pi deposition GaN were characterized by SEM, EDS, and XPS, respectively, which illustrated that Co-pi was successfully decorated on the surface of GaN. PEC measurement showed that photocurrent density of GaN was 0.5 mA/㎠ and that of Co-pi deposited GaN was 0.75 mA/㎠. Impedance and Mott-Schottky measurements were performed, and as a result of the measurement, polarization resistance (Rp) and increased donor concentration (ND) values decreased from 50.35 Ω to 34.16 Ω were confirmed. As a result of analyzing the surface components before and after the water decomposition, it was confirmed that the Co-pi catalyst is stable because Co-pi remains even after the water decomposition. Through this, it was confirmed that Co-pi is effective as a catalyst for improving GaN efficiency, and when applied as a catalyst to other photoelectrodes, it is considered that the efficiency of the PEC system can be improved.

A.C. Impedance Properties of HA/Ti Compound Layer coated Ti-30Ta-(3~15)Nb Alloys (Ti-30Ta-(3~15)Nb 합금에 HA/Ti 복합 코팅한 표면의 교류임피던스 특성)

  • Jeong, Y.H.;Lee, H.J.;Moong, Y.P;Park, G.H.;Jang, S.H.;Son, M.K.;Choe, H.C.
    • Journal of the Korean institute of surface engineering
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    • v.41 no.5
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    • pp.181-188
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    • 2008
  • A.C. impedance properties of HA/Ti compound layer coated Ti-30Ta-($3{\sim}15$)Nb alloys have been studied by electrochemical method. Ti-30Ta binary alloys contained 3, 7, 10 and 15 wt% Nb were manufactured by the vacuum furnace system. And then specimen was homogenized at $1000^{\circ}C$ for 24 hrs. The sample was cut and polished for corrosion test and coating. It was coated with HA/Ti compound layer by magnetron sputter. The non-coated and coated morphology of Ti alloy were analyzed by X-ray diffractometer (XRD), energy X-ray dispersive spectroscopy (EDX) and filed emission scanning electron microscope (FE-SEM). The corrosion behaviors were investigated using A.C. impedance test (PARSTAT 2273, USA) in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. Ti-30Ta-($3{\sim}15\;wt%$)Nb alloys showed the ${\alpha}+{\beta}$ phase, and $\beta$ phase peak was predominantly appeared in the case of increasingly Nb contents. The microstructures of Ti alloy were transformed from needle-like structure to equiaxed structure as Nb content increased. From the analysis of coating surface, HA/Ti composite surface uniformed coating layer with 750 nm thickness. The growth directions of film were (211), (112), (300) and (202) for HA/Ti composite coating on the surface after heat treatment at $550^{\circ}C$, whereas, the growth direction of film was (110) for Ti coating. The polarization resistance ($R_p$) of HA/Ti composite coated Ti-alloys were higher than those of the Ti and HA coated samples in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. Especially, corrosion resistance of Ti-Ta-Nb system increased as Nb content increased.