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Lee, Tae-Hee,Jeon, Sang-Yun,Im, Ha-Ni,Song, Sung-Ju 한국전력공사 2021 KEPCO Journal on electric power and energy Vol.7 No.1
In general, SOFCs mainly use Ni-YSZ cermet, a mixture of Ni and YSZ, as an anode material, which is stable in a high-temperature reducing atmosphere. However, when SOFCs have operated at a high temperature for a long time, the structural change of Ni occurs and it results in the problem of reducing durability and efficiency. Accordingly, a development of a new anode material that can replace existing nickel and exhibits similar performance is in progress. In this study, SrTiO<sub>3</sub>, which is a perovskite-based mixed conductor and one of the candidate materials, was used. In order to increase the electrical conduction properties, Y<sub>0.08</sub>Sr<sub>0.92</sub>Fe<sub>0.3</sub>Ti<sub>0.7</sub>O<sub>3</sub>, doped with 0.08 mol of Y<sup>3+</sup> in Sr-site and 0.03 mol of transition metal Fe<sup>3+</sup> in Ti-site, was synthesized and its chemical diffusion coefficient and reaction constant were measured. Its electrical conductivity changes were also observed while changing the oxygen partial pressure at a constant temperature. The performance as a candidate electrode material was verified by predicting the defect area through the electrical conductivity pattern according to the oxygen partial pressure.
Lee, Tae-Ryong,Im, Ha-Ni,Jeon, Sang-Yun,Yoo, Young-Sung,Chavan, Archana U.,Song, Sun-Ju The Electrochemical Society 2016 Journal of the Electrochemical Society Vol.163 No.7
<P>High temperature co-electrolysis of steam and CO2 based on solid oxide electrolysis cell (SOEC) to produce syngas as a feedstock for the well-known Fischer-Tropsch process is the main aim of the present research. Here Ni-8YSZ/8YSZ/LSCF6428-GDC button cells have been fabricated and the effect of the different microstructural parameters like air electrode thicknesses, fuel electrode porosities, adhesion layer and thermodynamic parameters like gas composition, temperature, on the performance of SOEC has been investigated systematically. The SOEC with 10 mu m air electrode thickness, functional layer, fuel electrode having 20 vol% PMMA content, addition of YSZ-GDC adhesion layer gives the better performance in overall results and the voltage obtained for this SOEC at current density of 0.8 A.cm(-2) is similar to 1.25 V at 800 degrees C in 49% N-2, 5% H-2, 23% CO2 and 23% H2O gas mixture at fuel electrode side. To identify the electrochemical processes occurring at the electrodes of SOEC, distribution function of relaxation time (DRT) analysis of the electrochemical impedance (EIS) data is carried out. (C) 2016 The Electrochemical Society. All rights reserved.</P>
Im, Ha-Ni,Kim, In-Ho,Singh, Bhupendra,Jeon, Sang-Yun,Yoo, Young-Sung,Song, Sun-Ju The Electrochemical Society 2017 Journal of the Electrochemical Society Vol.164 No.4
<P>In this work, we investigated charge transport properties of La0.1Sr0.9Co0.8Fe0.2O3-delta (LSCF1982) by a blocking cell experiment in isothermal conditions in 800-950 degrees C range. By measuring the ionic charge of transport (alpha(*)(i)) vs. oxygen partial pressure (pO(2)), the cross-effect between ionic and electronic flows were investigated. The values of alpha(*)(i) were found to be non-zero with a magnitude of 0.43-1.15 in 800-950 degrees C range, indicating that even in the absence of a direct cause of electron flow a significant number of electrons are dragged by the cations. By constructing an Onsager matrix, the values of Onsager transport coefficients were extracted. It was observed that the Onsager coefficients related with the cross-effect (L-ie = L-ei) have nearly of the same order of magnitude that of the Onsager coefficient for ionic flow (L-ii) and therefore cannot be ignored. The values of partial ionic conductivity were calculated from Onsager matrix and which showed an exponential increase (sigma O-2-alpha pO(2)(m), m = 1/2) with increasing pO(2) and temperature at 800 degrees C but less dependence on pO(2) at the higher temperatures. (C) 2017 The Electrochemical Society. All rights reserved.</P>
Im, Ha-Ni,Choi, Moon-Bong,Singh, Bhupendra,Lim, Dae-Kwang,Song, Sun-Ju The Electrochemical Society 2015 Journal of the Electrochemical Society Vol.162 No.7
<P>The oxygen reduction reaction (ORR) on La0 1Sr0.9Co0.8Fe0.2O3-delta (LSCF1982) electrode is investigated by electrochemical impedance spectroscopy (EIS) in 550-650 degrees C range under different oxygen partial pressures (pO(2)). The distribution function of relaxation time (DAT) analysis of EIS data enabled us to distinguish 3 individual sub-processes contributing toward the overall electrode polarization during ORR. Based on these results, oxygen chemical diffusivity (D-chem) and surface exchange coefficient (K-sur) values are obtained under open circuit voltage (OCV) conditions by Gerischer impedance model. In 500-650 degrees C range, K-sur values ranges between 10(-5)-10(-8) cm.s(-1) and D-chem, values are in 10(-4)-10(-6) cm(2).s(-1) range which, due to the higher ionic conductivity of LSCF1982, is relatively higher than those for similar mixed-conducting LaxSr1-xCo1-yFeyO3-delta (LSCF). The values of activation overpotential are separated under the fixed current load, which are well-fitted to the Butler-Volmer equation. Under the current load, the variation of exchange current density (i(0)) with pO(2) indicated that at the high temperature the total reaction-rate is determined by charge transfer reaction, but when temperature is decreased the reaction-rate is determined by the gas diffusion reaction. (C) 2015 The Electrochemical Society. All rights reserved.</P>
Im, Ha-Ni,Singh, Bhupendra,Hong, Jae-Woon,Kim, In-Ho,Lee, Kang Taek,Song, Sun-Ju The Electrochemical Society 2016 Journal of the Electrochemical Society Vol.163 No.14
<P>In case of highly defective perovskite oxides such as La0.1Sr0.9Co0.8Fe0.2O3-delta (LSCF1982), the ionic defect has been in question by suggesting direct oxygen ion diffusion by considering lattice oxygen site as an interstitial rather than an oxygen vacancy. In the present study, the thermomigration of ionic defect species was measured by ionic thermopower measurement to provide strong evidence of interstitial diffusion and the defect structure was further analyzed in terms of effectively negatively charged oxygen interstitial as a charge-compensating defect against hole. Two kinds of holes-delocalized and localized at B-site cations; were investigated by defect chemical analysis. From the conductivity analysis based on the non-stoichiometry results, the contributions of delocalized holes, localized hole at Co site, localized hole at Fe site, and localized hole moving from Co site to Fe site were successfully separated, and it was observed that the hopping reaction involving hole localized at Co is dominant in conductivity mechanism. The measurement of electronic thermopower further confirms the involvement of two different types of holes in p-type conduction. (C) 2016 The Electrochemical Society. All rights reserved.</P>
Im, Ha-Ni,Jeon, Sang-Yun,Lim, Dae-Kwang,Singh, Bhupendra,Choi, Mihwa,Yoo, Young-Sung,Song, Sun-Ju The Electrochemical Society 2015 Journal of the Electrochemical Society Vol.162 No.1
<P>In this work, a YSZ electrolyte based solid oxide cell (SOC) with La0.6Sr0.4Co0.2Fe0.8O3-delta-Gd0.1Ce0.9O2-delta (LSCF6428-GDC) composite oxygen-electrode and a barrier layer of GDC between the electrolyte and oxygen electrode was fabricated and its performance was investigated while operating in fuel cell mode and steam/CO2 co-electrolysis mode in 700-850 degrees C range. The distribution of relaxation times (DRT) analysis of the electrochemical impedance spectroscopy (EIS) data was employed to isolate the contributions of electrode polarization processes. The reversibility of SOC was tested during the SOFC and steam/CO2 co-electrolysis operations at 800 degrees C. It was observed that at low current densities the current-voltage (i-V) curves showed good continuity across the open circuit voltage (OCV) but minor fluctuations in the SOC performance were observed at the higher current densities, which could be due to the gas-diffusion limitation of the reactants inside the electrodes or the microstructural changes occurring due to the electrode degradation. (C) 2015 The Electrochemical Society. All rights reserved.</P>
Im, Ha-Ni,Jeon, Sang-Yun,Choi, Moon-Bong,Singh, Bhupendra,Song, Sun-Ju The Electrochemical Society 2013 Journal of the Electrochemical Society Vol.160 No.9
<P>Oxygen nonstoichiometry (δ) and transport properties of Y<SUB>0.08</SUB>Sr<SUB>0.92</SUB>Fe<SUB>0.1</SUB>Ti<SUB>0.9</SUB>O<SUB>3-δ</SUB> (YSFT01) were assessed for the understanding of charge compensation mechanism, and electronic and transport behavior of co-doped SrTiO<SUB>3</SUB> systems having transition metal acceptor-cation, which are being considered as potential anode materials in solid oxide fuel cell (SOFC). Oxygen nonstoichiometry of YSFT01 was measured by thermogravimetric analysis (TGA) as a function of oxygen partial pressure ([Formula]) and temperature. The δ isotherms indicated that the valence of the variable-valence acceptor cation Fe changed from Fe<SUP>3+</SUP> to Fe<SUP>2+</SUP> with decreasing [Formula]. Total conductivity of YSFT01 showed a δ-dependent trend and in p-type region when Fe existed as Fe<SUP>3+</SUP>, total conductivity decreased with decreasing [Formula], but in n-type region when Fe<SUP>3+</SUP> started reducing to Fe<SUP>2+</SUP>, total conductivity increased with decreasing [Formula]. The chemical diffusivity ([Formula]) and surface exchange coefficient (<I>k</I>) of oxygen were calculated from the DC conductivity relaxation measurement and at 1000°C they were 8.1 × 10<SUP>−6</SUP> cm<SUP>−2</SUP> s<SUP>−1</SUP> and 3.3 × 10<SUP>−4</SUP> cm s<SUP>−1</SUP>, respectively. Oxygen-ion conductivity was calculated as a function of [Formula] from the chemical diffusivity and nonstoichiometry results, and it increased with increasing temperature; it was nearly constant in higher [Formula] regime but in low [Formula] regime it increased with decreasing [Formula].</P>
Hong, Jaewoon,Balamurugan, Chandran,Im, Ha-Ni,Jeon, Sang-Yun,Yoo, Young-Sung,Song, Sun-Ju The Electrochemical Society 2018 Journal of the Electrochemical Society Vol.165 No.3
<P>Ni-YSZ/YSZ/GDC/LSCF6428-GDC10 solid oxide cells were fabricated and investigated in high-temperature H2O/CO2 co-electrolysis using various inlet fuel compositions at 800 degrees C. Furthermore, to see the effect of infiltration on co-electrolysis, the precursor solution for a 10% gadolinium-doped ceria (GDC10) catalyst was dispersed into a fuel electrode backbone by a controlled urea/cation infiltration method. The influence of the inlet gas composition on the syngas product ratio was investigated by in-line gas chromatography. To understand the high-temperature H2O/CO2 co-electrolysis cell performance, electrochemical impedance spectroscopy (EIS) under open-circuit voltage and I-V characteristics, by the electrochemical reactions occurring at the electrodes of prepared solid oxide electrolysis cell (SOEC) were examined. When the inlet gas composition was N-2 63.5%, H-2 5%, CO2 11.5% and H2O 20% under electrolysis current density at -0.6 A cm(-2), the H-2/CO ratio of infiltrated cell was improved from 2.1 to 2.8 compared with the non-infiltrated cell. The thermodynamic factors determining the size, morphology and shape of the infiltrated particles were discussed. (C) The Author(s) 2018. Published by ECS.</P>
Lim, Dae-Kwang,Im, Ha-Ni,Singh, Bhupendra,Song, Sun-Ju The Electrochemical Society 2015 Journal of the Electrochemical Society Vol.162 No.6
<P>The performance of a proton-conducting ceramic-electrolyte fuel cell (PCFC) with BaCe<SUB>0.85</SUB>Y<SUB>0.15</SUB>O<SUB>3-δ</SUB> (BCY15) electrolyte, NiO-BCY15 anode and La<SUB>0.8</SUB>Sr<SUB>0.2</SUB>MnO<SUB>3</SUB> (LSM) cathode is analyzed in different gas conditions in 600–750°C range. The distribution of relaxation time (DRT) analysis of the electrochemical impedance spectroscopy (EIS) data obtained by varying the gas-flow rate, water vapor pressure (<I>p</I>H<SUB>2</SUB>O) and oxygen partial pressure (<I>p</I>O<SUB>2</SUB>) is performed to identify the major electrode sub-processes involved in overall electrode reactions. The study of variations in cathodic <I>p</I>O<SUB>2</SUB> shows that the cathodic polarization due to the charge transfer reaction is the major contributor toward the overall electrode polarization resistance. The effect of electrolyte thickness on the fuel cell performance is also studied and a peak power density of ∼0.76 W⋅cm<SUP>−2</SUP> at a current density of ∼1.95 A⋅cm<SUP>−2</SUP> is achieved at 750°C with 8 μm thick electrolyte. The PCFC shows stable performance without any sign of material degradation during the long term operation at a fixed input current for 100 h. The fuel cell performance is compared with those of similar PCFCs with Ba<SUB>0.5</SUB>Sr<SUB>0.5</SUB>Co<SUB>0.8</SUB>Fe<SUB>0.2</SUB>O<SUB>3-δ</SUB> (BSCF5582), LSM-GDC, and LSM-BCY15 as cathodes, and possible reasons for the observed difference is discussed in terms of the nature of their conductivity.</P>