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김주식,변수일 한국전기화학회 2005 한국전기화학회지 Vol.8 No.2
This article covers the theoretical ac-impedance models for the analysis of oxygen reduction on the porous cathode electrode for solid oxide fuel cell (SOFC). Firstly, ac-impedance models were explained on the basis of the mechanism of oxygen reduction, which were classified into the rate-determining steps; (i) adsorption of oxygen atom on the electrode surface, (ii) diffusion of adsorbed oxygen atom along the electrode surface towards the three-phase (electrode/electrolyte/gas) boundaries, (iii) surface diffusion of adsorbed oxygen atom mixed with the adsorption reaction of oxygen atom on the electrode surface and (iv) diffusion of oxygen vacancy through the electrode coupled with the charge transfer reaction at the electrode/gas interface. In each section for ac-impedance model, the representative impedance plots and the interpretation of important parameters attributed to the oxygen reduction reaction were explained. Finally, we discussed in detail the applications of the proposed theoretical ac-impedance models to the real electrode of SOFC system.
Kim, Ju-Sik,Pyun, Su-Il The Korean Electrochemical Society 2005 한국전기화학회지 Vol.8 No.2
This article covers the theoretical ac-impedance models for the analysis of oxygen reduction on the porous cathode electrode f3r solid oxide fuel cell (SOFC). Firstly, ac-impedance models were explained on the basis of the mechanism of oxygen reduction, which were classified into the rate-determining steps; (i) adsorption of oxygen atom on the electrode surface, (ii) diffusion of adsorbed oxygen atom along the electrode surface towards the three-phase (electrode/electrolyte/gas) boundaries, (iii) surface diffusion of adsorbed oxygen atom m ixed with the adsorption reaction of oxygen atom on the electrode surface and (iv) diffusion of oxygen vacancy through the electrode coupled with the charge transfer reaction at the electrode/gas interface. In each section for ac-impedance model, the representative impedance plots and the interpretation of important parameters attributed to the oxygen reduction reaction were explained. Finally, we discussed in detail the applications of the proposed theoretical ac-impedance models to the real electrode of SOFC system.
Mills, Edmund M.,Min, Bok Ki,Kim, Seong K.,Kim, Seong Jun,Kang, Min-A,Song, Wooseok,Myung, Sung,Lim, Jongsun,An, Ki-Seok,Jung, Jongwan,Kim, Sangtae American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.33
<P>Graphene barristors are a novel type of electronic switching device with excellent performance, which surpass the low on–off ratios that limit the operation of conventional graphene transistors. In barristors, a gate bias is used to vary graphene’s Fermi level, which in turn controls the height and resistance of a Schottky barrier at a graphene/semiconductor heterojunction. Here we demonstrate that the switching characteristic of a thin-film ZnO/graphene device with simple geometry results from tunneling current across the Schottky barriers formed at the ZnO/graphene heterojunctions. Direct characterization of the current–voltage−temperature relationship of the heterojunctions by ac-impedance spectroscopy reveals that this relationship is controlled predominantly by field emission, unlike most graphene barristors in which thermionic emission is observed. This governing mechanism makes the device unique among graphene barristors, while also having the advantages of simple fabrication and outstanding performance.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-33/acsami.5b03380/production/images/medium/am-2015-03380u_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b03380'>ACS Electronic Supporting Info</A></P>
Min, Bok Ki,Kim, Seong K.,Kim, Seong Ho,Kang, Min-A,Noothongkaew, Suttinart,Mills, Edmund M.,Song, Wooseok,Myung, Sung,Lim, Jongsun,Kim, Sangtae,An, Ki-Seok American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.41
<P>A comprehensive study for the effect of interfacial buffer layers on the electrical transport behavior in CVD-grown graphene based devices has been performed by ac-impedance spectroscopy (IS) analysis. We examine the effects of the trap charges at graphene/SiO2 interface on the total capacitance by introducing self-assembled monolayers (SAMs). Furthermore, the charge transports in the polycrystalline graphene are characterized through the temperature-dependent IS measurement, which can be explained by the potential barrier model. The frequency-dependent conduction reveals that the conductivity of graphene is related with the mobility, which is limited by the scattering caused by charged adsorbates on SiO2 surface.</P>
GNP법을 이용한 고체산화물 연료전지의 공기극용 La0.75Sr0.25FeO3의 제조 및 특성
신동열,박주현,손희정,임탁형,이승복,윤기석,윤순길,송락현 한국전기화학회 2007 한국전기화학회지 Vol.10 No.1
Glycine Nitrate Process (GNP)를 이용하여 La0.75Sr0.25FeO3를 합성하였다. 이때, GNP의 글리신의 함량은 화학양론식 으로 계산하여 3.17 mol을 첨가하였다. ICP-AES분석으로 각각의 조성 함량을 조사하고, XRD, SEM 분석으로 합성된 분말의 결정성과 입자크기를 분석하였다. 이렇게 분석한 분말은 일축가압 성형으로 펠렛을 제조하였으며, 이 시편은 1200oC에서 소결하였다. 소결된 시편은 아르키메데스 법을 이용하여 소결밀도를 측정하였다. 전기화학적 성능을 평가하 기 위해 AC impedance spectroscopy로 측정하였으며, GNP 법으로 합성된 LSF가 기존의 LSM 보다 낮은 Ohmic resistance 및 Polarization resistance를 보임을 확인하였다. 또한 합성된 LSF를 양극으로 사용하여 연료극 지지체식 고체산화물 연료전지의 단위전지를 제작하였으며, 그 성능은 750oC에서 342 mW/cm2 (0.7 V, 488 mA/cm2)을 나타내었 다. 마지막으로 임피던스 분석에 의하여 단위전지의 전기화학적 분극저항을 평가하였다.
GNP법을 이용한 고체산화물 연료전지의 공기극용 La<sub>0.75</sub>Sr<sub>0.25</sub>FeO<sub>3</sub>의 제조 및 특성
박주현,손희정,임탁형,이승복,윤기석,윤순길,신동열,송락현,Park, Ju-Hyun,Son, Hui-Jeong,Lim, Tak-Hyoung,Lee, Seung-Bok,Yun, Ki-Seok,Yoon, Soon-Gil,Shin, Dong-Ryul,Song, Rak-Hyun 한국전기화학회 2007 한국전기화학회지 Vol.10 No.1
Glycine Nitrate Process(GNP)를 이용하여 $La_{0.75}Sr_{0.25}FeO_3$를 합성하였다. 이때, GNP의 글리신의 함량은 화학양론식으로 계산하여 3.17mol을 첨가하였다. ICP-AES분석으로 각각의 조성 함량을 조사하고, XRD, SEM분석으로 합성된 분말의 결정성과 입자크기를 분석하였다. 이렇게 분석한 분말은 일축가압 성형으로 펠렛을 제조하였으며, 이 시편은 $1200^{\circ}C$에서 소결하였다. 소결된 시편은 아르키메데스 법을 이용하여 소결밀도를 측정히였다. 전기화학적 성능을 평가하기 위해 AC impedance spectroscopy로 측정하였으며, GNP 법으로 합성된 LSF가 기존의 LSM 보다 낮은 Ohmic resistance및 Polarization resistance를 보임을 확인하였다. 또한 합성된 LSF를 양극으로 사용하여 연료극 지지체식 고체산화물 연료전지의 단위전지를 제작하였으며, 그 성능은 $750^{\circ}C$에서 $342mW/cm^2(0.7V,\;488mA/cm^2)$을 나타내었다. 마지막으로 임피던스 분석에 의하여 단위전지의 전기화학적 분극저항을 평가하였다. We synthesized and investigated $La_{0.75}Sr_{0.25}FeO_3$ by Glycine Nitrate Process(GNP) method used as cathode materials for SOFC(solid oxide fuel cell). Optimized amount of glycine is 3.17 mol. ICP elemental composition analysis indicated that the stoichiometry of the synthesized powders have nearly nominal values. SEM images and XRD patterns reveal that the synthesized powder has uniform size distribution and high degree of crystallinity. The sample powders were isostatically pressed to form a pellet. The green body was sintered at $1200^{\circ}C$ and the relative density of the sintered specimens were measured by Archimedes mettled. We measured electrochemical performance of LSF by AC impedance spectroscopy. Resistance of LSF shows lower value than that of LSM throughout all temperature region. The anode-supported solid oxide fuel cell showed a performance of $342mW/cm^2(0.7V,\;488mA/cm^2)$ at $750^{\circ}C$. The electrochemical characteristics of the single cell were examined by at impedance method.
Vaidya, Saiprasad,Allouche, Erez N. Techno-Press 2011 Smart Structures and Systems, An International Jou Vol.7 No.1
Geopolymer concrete is finding a growing number of niche applications in the field of civil engineering due to its high compressive strength and strength gain rate, retainage of structural properties in elevated temperature environments, chemical stability in highly acidic conditions and environmental benefits. Combining the above mentioned characteristics with induced electrical conductivity, could enable geopolymer cement to serve as a smart and sustainable cementitious material suitable for health monitoring of civil structures. Carbon fibers were added to fresh geopolymer and OPC (ordinary Portland cement) mixes to enhance their electrical conductivities. AC-impedance spectroscopy analysis was performed on the specimens with fiber fraction ranging from 0.008 to 0.8 with respect to the weight of cementitious binder, to measure their electrical resistivity values and to determine the maximum beneficial fiber content required to attain electrical percolation. Experimental observations suggest that CFR-geopolymer cement exhibits superior performance to CFR-OPC in terms of conducting electrical current.
박주현,이승복,손희정,임탁형,윤순길,신동렬,송락현,Park, Ju-Hyun,Lee, Seung-Bok,So, Hui-Jeong,Lim, Tak-Hyoung,Yoon, Soon-Gil,Shin, Dong-Ryul,Song, Rak-Hyun 한국전기화학회 2008 한국전기화학회지 Vol.11 No.2
GNP(Glycine Nitrate Process)을 이용하여$(La_{0.75}Sr_{0.25})_{1-x}FeO_{3-\delta}$를 합성하고, perovskite의 A-site deficiency에 따른 특성을 분석하기 위해 x=0, 0.02, 0.04, 0.06, 0.08로 바꾸어 합성하였다. SEM과 XRD분석을 통하여 균질하고 결정성이 높은 분말이 합성된것을 확인하였으며, 4단자법과 AC impedance spectroscopy를 통하여 전도도는 x = 0.02가 $750^{\circ}C$ $155{\Omega}cm^2$로 가장 우수하였으며, AC impedance결과 역시 x = 0.02가 가장 낮은 분극저항과 활성화 에너지를 가지고 있었다. 이 결과 Perovskite의 A-site deficiency를 가함에 따라 산소 결핍 및 구조의 변화가 생겼으며 이로 인해 전도도와 분극 저항, 활성화 에너지에 영향을 미친 것을 알 수 있었다. 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.
고체산화물 연료전지의 공기극용 ABO3 구조의(La0.75Sr0.25)1-x FeO3-∂의 A-site변화에 따른 전극 특성 연구
박주현,윤순길,이승복,손희정,임탁형,신동렬,송락현 한국전기화학회 2008 한국전기화학회지 Vol.11 No.2
GNP(Glycine Nitrate Process)을 이용하여 (La0.75Sr0.25)1-xFeO3-δ를 합성하고, perovskite의 A-site deficiency에 따른 특 성을 분석하기 위해 x = 0, 0.02, 0.04, 0.06, 0.08로 바꾸어 합성하였다. SEM과 XRD 분석을 통하여 균질하고 결정성 이 높은 분말이 합성된것을 확인하였으며, 4단자법과 AC impedance spectroscopy를 통하여 전도도는 x = 0.02가 750 oC 155 Ωcm2로 가장 우수하였으며, AC impedance결과 역시 x = 0.02가 가장 낮은 분극저항과 활성화 에너지를 가지고 있 었다. 이 결과 Perovskite의 A-site deficiency를 가함에 따라 산소 결핍 및 구조의 변화가 생겼으며 이로 인해 전도도와 분극 저항, 활성화 에너지에 영향을 미친 것을 알 수 있었다