Intermediate Temperature-operating Solid Oxide Fuel Cell Research Articles

Electrochemical properties of B-site non-stoichiometric layered perovskite SmBa0.5Sr0.5CoxO5+d (x=1.9–2.1) cathodes for IT-SOFC

In this study, layered perovskites were synthesized using a non-stoichiometric synthesis strategy that allowed the variation of the amount of Co substitution in the basic composition of SmBa0.5Sr0.5Co2O5+d (SBSCO), used as a cathode material for Intermediate Temperature-operating Solid Oxide Fuel Cells (IT-SOFCs).SmBa0.5Sr0.5CoxO5+d (x = 1.9–2.1, SBSCO-1.9–2.1), B-site non-stoichiometric layered perovskites, were analyzed to characterize the electrical and electrochemical properties with respect to the Co substitution. Among them, SmBa0.5Sr0.5Co2.05O5+d (SBSCO-2.05) exhibited the best electrical and electrochemical properties with an ASR of 0.082 Ωcm2 and an electrical conductivity of 268.42 S/cm at 700 °C (measured in air within a series of measurements of increasing measuring temperature). Therefore, B-site non-stoichiometric perovskite compositions with increased Co substitution on their B sites represent a key strategy for achieving high performance cathodes compared to cathodes with stoichiometric compositions.

Pr- and Sm-Substituted Layered Perovskite Oxide Systems for IT-SOFC Cathodes

In this study, the phase synthesis and electrochemical properties of A/A//A///B2O5+d (A/: Lanthanide, A//: Ba, and A//: Sr) layered perovskites in which Pr and Sm were substituted at the A/-site were investigated for cathode materials of Intermediate Temperature-Operating Solid Oxide Fuel cells (IT-SOFC). In the PrxSm1−xBa0.5Sr0.5Co2O5+d (x = 0.1–0.9) systems, tetragonal (x < 0.4) and orthorhombic (x ≥ 0.5) crystalline structures were confirmed according to the substitution amount of Pr, which has a relatively large ionic radius, and Sm, which has a small ionic radius. All of the layered perovskite oxide systems utilized in this study presented typical metallic conductivity behavior, with decreasing electrical conductivity as temperature increased. In addition, Pr0.5Sm0.5Ba0.5Sr0.5Co2O5+d (PSBSCO55), showing a tetragonal crystalline structure, had the lowest conductivity values. However, the Area-Specific Resistance (ASR) of PSBSCO55 was found to be 0.10 Ω cm2 at 700 °C, which is lower than those of the other compositions.

Enhanced Electrochemical Properties of Non-stoichiometric Layered Perovskites, Sm1-xBaCo2O5+d, for IT-SOFC Cathodes.

In this study, electrochemical properties of layered perovskites having non-stoichiometric compositions (Sm1−xBaCo2O5+d, x = 0, 0. 01, 0.02, 0.03, 0.04, 0.05, 0.10, and 0.15) were analyzed for the direct application of cathode materials for Intermediate Temperature-operating Solid Oxide Fuel Cells (IT-SOFC). From the Sm1−xBaCo2O5+d oxide systems calcined at 1,100°C for 8 h, single phase (SmBaCo2O5+d, SBCO_1) was maintained only in the case of the x = 0 composition. In the compositions of x = 0.05–0.10, BaCoO2.6 was mixed with the pattern of SBCO. In addition, in the composition of x = 0.15, it was confirmed that BaCoO2.6 and CoO phases coexisted with SBCO. In the compositions of Sm1−xBaCo2O5+d, the overall Area Specific Resistance (ASR) values decreased as the removal amount of Sm increased from x = 0–0.10; then, the values increased for compositions from x = 0.15. For example, the ASRs of SBCO_1, Sm0.95BaCo2O5+d (SBCO_0.95), Sm0.90BaCo2O5+d (SBCO_0.90), and Sm0.85BaCo2O5+d (SBCO_0.85) measured at 600°C were 0.301, 0.147, 0.119, and 0.179 Ω cm2, respectively. In particular, SBCO_0.90 was found to have an excellent ASR property of about 0.035 Ω cm2 at 700°C. Typical properties of the metal–insulator transition (MIT) electrical conductivity were shown in all measured compositions. The temperature at which MIT occurred increased as the non-stoichiometric composition increased.

Synthesis and electrochemical properties of layered perovskite substituted with heterogeneous lanthanides for intermediate temperature-operating solid oxide fuel cell

In this study, phase synthesis and electrochemical properties of Sm1-xNdxBa0.5Sr0.5Co2O5+d (x = 0–0.9) oxide systems where neodymium and samarium were replaced at the A-site of SmBa0.5Sr0.5Co2O5+d layered perovskite are investigated for use as cathode materials in Intermediate Temperature-operating Solid Oxide Fuel Cells (IT-SOFCs).The structure of Sm1-xNdxBa0.5Sr0.5Co2O5+d (x = 0–0.9) oxide systems can exist in either an orthorhombic (x = 0–0.4) or tetragonal (x = 0.5–0.9) form. The maximum electrical conductivities in Sm1-xNdxBa0.5Sr0.5Co2O5+d (x = 0–0.9) oxide systems were obtained from Sm0.2Nd0.8Ba0.5Sr0.5Co2O5+d (SNBSCO8) and their values are 1280 and 280 Scm−1 at 50 °C and 900 °C, respectively. The area specific resistances (ASRs) of SBSCO are 3.019, 0.611, and 0.092 Ωcm2 at 500, 600, and 700 °C, respectively. However, SNBSCO8 single phase gives the lowest ASRs of 1.751, 0.244 and 0.044 Ωcm2 at the same temperatures tested. SNBSCO8 is thus a promising candidate cathode material for IT-SOFC applications.

중·저온형 고체산화물 연료전지 공기극 물질로 사용되는 이중층 페로브스카이트와 컴플렉스 페로브스카이트의 전기 전도도 비교

Electrical conductivities of complex perovskites, layered perovskite and Sr doped layered perovskite oxides were measured and analyzed for cathode materials of Intermediate Temperature-operating Solid Oxide Fuel Cells (IT-SOFCs). The electrical conductivities of Sm 1-x Sr x CoO 3-δ (x = 0.3 and 0.7) exhibit a metal?insulator transition (MIT) behavior as a function of temperature. However, Sm 0.5 Sr 0.5 CoO 3-δ (SSC55) shows metallic conductivity characteristics and the maximum electrical conductivity value compared to the values of Pr 0.5 Sr 0.5 CoO 3-δ (PSC55) and Nd 0.5 Sr 0.5 CoO 3-δ (NSC55). The electrical conductivity of SmBaCo 2 O 5+δ (SBCO) exhibits a MIT at about 250℃. The maximum conductivity is 570 S/cm at 200℃ and its value is higher than 170 S/cm over the whole temperature range tested. SmBa 0.5 Sr 0.5 Co 2 O 5+δ (SBSCO), 0.5 mol% Sr and Ba substituted at the layered perovskite shows a typically metallic conductivity that is very similar to the behavior of the SSC55 cathode, and the maximum and minimum electrical conductivity in the SBSCO are 1280 S/cm at 50℃ and 280 S/cm at 900℃.

Effects of infiltrated Sr and Mn doped LaCrO3 on porous La0.8Sr0.2Ga0.8Mg0.2O3-δ scaffolds used as anodes in solid oxide fuel cells

The phase stability and electrochemical properties of infiltrated anode catalysts on porous La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) scaffold are investigated for possible applications as anode materials for an intermediate temperature-operating solid oxide fuel cell (IT-SOFC). To avoid the formation of secondary phases between the anode and the LSGM electrolyte, an infiltration method is proposed on the porous LSGM scaffold. No secondary phases between the infiltrated La0.75Sr0.25Cr0.5Mn0.5O3 (LSCM) catalyst and the LSGM are observed at 900 °C. However, LaSrGa3O7, LaSrGaO4 and other unknown secondary phases are formed above the calcination temperature of 1000 °C when LSCM was infiltrated on porous LSGM scaffolds. The current (I)–voltage (V) characteristics are measured in an LSGM electrolyte single cell with a Ba0.5Sr0.5Co0.2Fe0.8O3-δ (BSCF) cathode and LSCM infiltrated into the LSGM scaffold type anode. The maximum power density of the single cell is 0.214 W cm− 2 at 800 °C.

중·저온형 고체산화물 연료전지 공기극의 적용을 위한 Sr이 치환된 이중층 페로브스카이트 기반 복합공기극 물질의 분말 크기 및 열 사이클에 따른 전기화학특성 분석

본 연구에서는 Sr이 치환된 이중층 페로브스카이트(<TEX>$SmBa_{0.5}Sr_{0.5}Co_2O_{5+{\delta}}$</TEX>, SBSCO)와 전해질 물질로 사용되는 <TEX>$Ce_{0.9}Gd_{0.1}O_{2-{\delta}}$</TEX> (CGO91)을 기반으로 한 중 저온형 고체산화물 연료전지 (ITSOFC) 복합공기극의 분말 크기와 열 사이클에 대한 전기화학특성을 연구하였다. 복합공기극의 모체가 되는 SBSCO에 CGO91물질을 이용하여 면적비저항을 확인 한 결과 약 <TEX>$0.54\sim9.04{\mu}m$</TEX>의 분말 크기를 보이는 SBSCO와 <TEX>$0.4\sim42{\mu}m$</TEX>의 분말 크기를 보인 CGO91이 각각 50 wt%로 구성된 SBSCO : 50 복합공기극이 600 및 <TEX>$700^{\circ}C$</TEX>에서 약 0.102 및 <TEX>$0.013{\Omega}cm^2$</TEX>의 우수한 면적비 저항을 가지는 것을 확인 하였으며 상대적으로 분말 크기가 큰 CGO91 분말을 이용한 두 개의 공기극의 경우 <TEX>$700^{\circ}C$</TEX>에서 약 <TEX>$0.260{\Omega}cm^2$</TEX>와 <TEX>$0.055{\Omega}cm^2$</TEX>의 특성을 보여주었다. 10회에 걸친 열 사이클실험을 통하여 SBSCO : 50의 면적비저항은 <TEX>$0.0193{\Omega}cm^2$</TEX>에서 <TEX>$0.094{\Omega}cm^2$</TEX>로 증가하였으며 7회 이후의 면적비저항은 일정하게 유지됨을 확인하였다. The electrochemical characteristics from various particle sizes of <TEX>$Ce_{0.9}Gd_{0.1}O_{2-{\delta}}$</TEX> (CGO91) in composite cathode comprised of the samarium-strontium doped layered perovskite (<TEX>$SmBa_{0.5}Sr_{0.5}Co_2O_{5+{\delta}}$</TEX>) and CGO91 have been investigated for possible application as a cathode material for an intermediate temperature-operating solid oxide fuel cell (IT-SOFC). The area specific resistances (ASRs) of composite cathodes with CGO91 having smaller particle size (<TEX>$0.4\sim42{\mu}m$</TEX>) and SBSCO of 1 : 1 ratio (50wt% SBSCO and 50 wt% CGO91, SBSCO: 50) give the lowest ASR of <TEX>$0.10{\mu}cm^2$</TEX> at <TEX>$600^{\circ}C$</TEX> and <TEX>$0.013{\Omega}cm^2$</TEX> at <TEX>$700^{\circ}C$</TEX>. However, composite cathodes with having relatively bigger CGO91 particle size show the two times higher ASR results than those of SBSCO : 50. From the 10 times thermal cycles in SBSCO : 50, the ASRs of SBSCO : 50 increased from <TEX>$0.0193{\Omega}cm^2$</TEX> to <TEX>$0.094{\Omega}cm^2$</TEX> at <TEX>$700^{\circ}C$</TEX>, however, the ASR value was maintained after 7 times of thermal cycling.

X-ray photoelectron spectroscopy analysis of (Ln 1− xSr x)CoO 3− δ (Ln: Pr, Nd and Sm)

The chemical states of the surface of (Ln 0.5Sr 0.5)CoO 3− δ (Ln (lanthanides) = Pr, Nd and Sm) used for cathode materials of intermediate temperature operating solid oxide fuel cells (IT-SOFCs) were investigated by X-ray photoelectron spectroscopy (XPS). Oxygen peaks comprised of lower binding energy (LBE) and higher binding energy (HBE) peaks from (Ln 0.5Sr 0.5)CoO 3− δ and Pr 0.3Sr 0.7CoO 3− δ (PSC37) showed that some merged oxygen peak behavior is a function of the Sr and lanthanide concentrations. By investigating the oxygen peaks, it was determined that more oxygen vacancies were generated on the surface of the cathodes when the lanthanides and Sr were substituted into perovskite oxides. When comparing the binding energies (BEs) of PSC37 with Pr 0.5Sr 0.5CoO 3− δ (PSC55), the LBE and HBE of the Sr peaks both increased when Sr was substituted at the A-site of a perovskite. Surface analysis of the Co peak on the surface of the cathode materials showed that the Co exists mainly as Co 3+ and partially oxidized to Co 4+ on the cathode materials. The partial existence of Co 4+ can provide some polaron hopping providing electronic conduction for the solid oxide fuel cell.

Optimization of La 0.6Ca 0.4Fe 0.8Ni 0.2O 3–Ce 0.8Sm 0.2O 2 composite cathodes for intermediate-temperature solid oxide fuel cells

Sample of nominal composition La 0.6Ca 0.4Fe 0.8Ni 0.2O 3 (LCFN) was prepared by liquid mix method. The structure of the polycrystalline powder was analyzed with X-ray powder diffraction data. This compound shows orthorhombic perovskite structure with a space group Pnma. In order to improve the electrochemical performance, Sm-doped ceria (SDC) powder was added to prepare the LCFN–SDC composite cathodes. Electrochemical characteristics of the composites have been investigated for possible application as cathode material for an intermediate-temperature-operating solid oxide fuel cell (IT-SOFC). The polarization resistance was studied using Sm-doped ceria (SDC). Electrochemical impedance spectroscopy measurements of LCFN–SDC/SDC/LCFN–SDC test cell were carried out. These electrochemical experiments were performed at equilibrium from 850 °C to room temperature, under both zero dc current intensity and air. The best value of area-specific resistance (ASR) was for LCFN cathode doped with 10% of SDC (LCFN–SDC9010), 0.13 Ω cm 2 at 850 °C. The dc four-probe measurement exhibits a total electrical conductivity over 100 S cm −1 at T ≥ 600 °C for LCFN–SDC9010 composite cathode.

SmBaCo2O5+d and LnBa0.5Sr0.5Co2O5+δ, Potential Cathode Materials for IT-SOFC

The electrical conductivity of SmBaCo2O5+δ (SBCO) showed a Metal-Insulator Transition (MIT) at about 200åC with maximum conductivity of 570 Scm-1 at 200oC and minimum conductivity 170 Scm-1 at 900oC. The area specific resistance (ASR) of composite cathode (50wt% of SBCO and 50wt% of Ce0.9Gd0.1O2, SBCO:50) on a Ce0.9Gd0.1O2 (CGO91) electrolyte was observed to be 0.05Ωcm2 at 700oC. SmBa0.5Sr0.5Co2O5+δ (SBSCO) electrode was sintered onto CGO91 at 1000oC to form symmetrical cells and exhibited an ASR value of 0.092 Ωcm2 at 700oC. The lowest ASR value was observed when the composite cathode of 50wt% of SBSCO and 50wt% of CGO91 (SBSCO:50) was used and these were 0.10 Ωcm2 at 600oC and 0.013 Ωcm2 at 700oC, respectively. The coefficient of thermal expansion (CTE) was 21.9 x 10-6 K-1 at 700oC. However, the CTE of SBSCO:50 was shown to be 13.6 x 10-6 K-1 at 700oC which are similar to the value of CGO91 electrolyte for intermediate temperature-operating solid oxide fuel cell (IT-SOFC) applications.

Cathode Properties of SmxSr1−x(Co,Fe,Ni)O3−δ/Sm0.2Ce0.8O1.9 Composite Material for Intermediate Temperature-Operating Solid Oxide Fuel Cell

Perovskite-structured cathode material containing samarium (Sm) has been recognized as a promising electrode material due to its high electrocatalytic property for intermediate temperature-operating solid oxide fuel cell (IT-SOFC). This research investigated the optimized composition of SmxSr1−x(Co,Fe,Ni)O3−δ/Sm0.2Ce0.8O1.9 on the Sm0.2Ce0.8O1.9 electrolyte and the possible use of an optimized composite material for the IT-SOFC system. The electrochemical and thermal properties of SmxSr1−x(Co,Fe,Ni)O3−δ and its composite material with the Sm0.2Ce0.8O1.9 electrolyte were investigated in terms of area specific resistance (ASR) and thermal expansion coefficient at various temperature conditions. Durability of the selected materials was verified by thermal cycling and long-term degradation tests. Sm0.5Sr0.5CoO3−δ and the Sm0.5Sr0.5CoO3−δ/Sm0.2Ce0.8O1.9(6:4) composite cathode showed a very low ASR of 0.87 Ωcm2 and 0.30 Ωcm2 at 600°C, respectively. The composite type cathode for the Sm0.5Sr0.5CoO3−δ material was more attractive due to its thermal expansion compatibility with neighboring cell components.

Performance analysis of cobalt-based cathode materials for solid oxide fuel cell

The area specific resistance (ASR) characteristics of Ln 1 − x Sr x M ′ 1 − y M″ y O 3 – δ (Ln=Lanthanides, M′ and M″: transition metal such as Co and Fe), Sm 0.5Sr 1.5Co 1 − y Ni y O 4 – δ and Sm 0.5Sr 1.5Co 1 − y Fe y O 4 – δ oxides were investigated as cathode materials for intermediate temperature operating solid oxide fuel cell (IT-SOFC) application. As an effect of Sr substitution in A-site of perovskite, ASR of Nd 0.5Sr 0.5CoO 3 (NSC55) was 0.14 Ω cm 2 at 700 °C. Sm 0.5Sr 0.5CoO 3 – δ (SSC55) on Ce 0.9Gd 0.1O 2 – δ (CGO91) and Ce 0.8Sm 0.2O 2 – δ (CSO82) showed the lowest ASR as 0.10 Ω cm 2 and 0.085 Ω cm 2 at 700 °C among various perovskite compositions in this study. ASR of B-site substituted Pr 0.3Sr 0.7Co 0.3Fe 0.7O 3 – δ (PSCF3737) in the Pr 0.3Sr 0.7Co 1 − y Fe y O 3 – δ was about 0.13 Ω cm 2 at 700 °C. Comparing ASR of SSC55 as a perovskite structure with the value of Sm 0.5Sr 1.5Co 1 − y Fe y O 4 – δ ( y = 0, 0.3, 0.5 and 0.7) as a spinel structure, the ASR of SSC55 was 0.085 Ω cm 2. However, the value of Sm 0.5Sr 1.5Co 1 − y Fe y O 4 – δ ( y = 0, 0.3, 0.5 and 0.7) was much higher than SSC55 at 700 °C. In XPS analyses, the atomic percentage values of PSC55 and PSC37 were 83.5, and 83.1%. However, the value of SrCoO 3 – δ was 50.2%. The results claim that more oxygen sites including oxygen vacancies on the surface of PSC55 and PSC37 exist than that of SrCoO 3 – δ .

Cathodic behavior of La 0.8Sr 0.2Co 1 − xMn xO 3 − δ perovskite oxide on YSZ electrolyte for intermediate temperature-operating solid oxide fuel cells

A study of the cathode properties of an intermediate temperature-operating solid oxide fuel cell (IT-SOFC) was carried out using La 0.8Sr 0.2Co 1 − x Mn x O 3 − δ (LSCM). LSCM-8246 had the lowest impedance on the 8 mol% yttria-stabilized zirconia (YSZ) electrolyte among the various compositions investigated in this study. A Ce 0.9Gd 0.1O 2 − δ (CGO) interlayer between LSCM and YSZ was introduced to inhibit the formation of resistive phases. Cathode impedance was decreased by approximately three times compared to that shown with non-interlayer samples. Investigation of the oxygen partial pressure dependence of LSCM-8246 on CGO-layered YSZ showed that the adsorbed oxygen ionization is the rate-determining step of the cathode reaction. The cathode material and structure can be applied to IT-SOFC at 700 °C because the area-specific resistance is sufficiently low, leading to a cell power density higher than 0.5 W/cm 2 at 0.7 V.

Characteristics of ABO 3 and A 2BO 4 (A [dbnd6]Sm, Sr; B [dbnd6]Co, Fe, Ni) samarium oxide system as cathode materials for intermediate temperature-operating solid oxide fuel cell

Samarium strontium cobalt oxide with ABO 3 lattice structure, which is mixed ionic and electronic conductor (MIEC), is considered as a promising cathode material for intermediate temperature-operating solid oxide fuel cell (IT-SOFC) due to its high electrocatalytic property. Cathode material containing cobalt (Co) is unstable at high temperature and has a relatively high thermal expansion coefficient. In this study, samarium oxide cathodes with ABO 3 and A 2BO 4 (A Sm, Sr; B Co, Fe, Ni) structure on Sm 0.2Ce 0.8O 1.9 electrolyte were investigated in terms of electrochemical property and thermal expansion property. Area specific resistance (ASR) was measured by ac impedance spectroscopy, and thermal expansion coefficient (TEC) was measured using a dilatometer. Microstructure of cathode was observed using a scanning electron microscopy. Sm 0.5Sr 0.5CoO 3−δ with ABO 3 structure showed the ASR of 0.87 Ωcm 2 at 600 °C, and Sm 0.5Sr 0.5NiO 3 ± δ , which actually has A 2BO 4 structure, showed the lowest TEC value of 13.3 × 10 − 6 /K.