Lanthanum Strontium Cobalt Ferrite Cathode Research Articles

Robust Pr6O11 infiltration for La0.6Sr0.4Co0.2Fe0.8O3-δ cathode performance enhancement on electrolyte supported solid oxide fuel cells

In this study, the infiltration of a novel electrocatalyst, Praseodymium oxide (Pr6O11), has successfully enhanced solid oxide fuel cell (SOFC) performance via simple infiltration method. Pristine Lanthanum strontium cobalt ferrite (LSCF) screen printed on a electrolyte supported SOFC button cell showed peak power density of 0.086 W/cm2 at 800 °C, infiltrating 0.1 mol/L of Pr6O11 precursor into the LSCF cathode increased performance by 16.3 % by recording a 0.100 W/cm2 peak power density and infiltrating higher concentration of 1 mol/L Pr6O11 precursor further increased power density to 0.118 W/cm2, a 37.2 % improvement. Although increasing temperature lowered the effectiveness of the electrocatalyst, 1 mol/L Pr6O11 precursor infiltrated LSCF still showed the highest peak power density overall with 0.237 W/cm2 at 900 °C, a 13.9 % increase from pristine LSCF's 0.208 W/cm2 at the same temperature. The results confirm that increasing Pr6O11 precursor concentration in infiltration solution is an effective way for improving SOFC performance.

Fabrication of Nano Samarium Doped Ceria(SDC) Infiltrated La6Sr4Co2Fe8O3-δ(LSCF) Composite Cathode for High Performance It-SOFCs

The solid oxide fuel cells(SOFCs) use oxygen ions generated by an oxygen reduction reaction(ORR) supplied to the cathode as charge carrier. Oxygen ions transferring across the solid oxide electrolyte via a hoping mechanism require a high operating temperature to overcome the low ionic conductivity. High ionic conductivity and performance can be obtained at high operating temperature, but the stability is reduced during operation condition due to deterioration of component materials and mutual chemical reactions at the interface. For this reason, researches have proceeded to lower operating temperature of to the intermediate temperature regime(650~750℃) and to develop the electrode layers having high performance at the lower operating temperature. However, since the oxygen reduction reaction resistance is increased, the performance of the SOFCs is reduced at the lower operating temperature. Therefore, many research institutes of fuel cells have added the composite cathode functional layer(CFL) to improve the fuel cell performance between electrolyte and electrode layers using various methods, composite powder, and infiltration. [1, 2] In this study, the solid oxide fuel unit cells are fabricated having the electrolyte/electrode composite layer which was applied to the LSCF electrode infiltrated with nanoparticle SDC for obtaining the many reaction site compared with conventional powder composite materials. When the LSCF-SDC composite cathode functional layer is manufactured, it is applied that the novel flash light sintering method replace the conventional thermal sintering method. Since it can finish the manufacturing process in seconds, the LSCF-SDC cathode layer has the LSCF cathode with nanoparticle SDC suppressed grain growth of the particles which can contribute to improving the performance of the fuel cells.[3] The microstructure of the infiltrated solution and the composite layer of the electrolyte material is analyzed using scanning electron microscopy (FE-SEM) and transmission electron microscopes energy dispersive spectroscopy (TEM-EDS). The crystallinity of nanoparticle SDC is analyzed using FR-TEM and X-ray diffraction. And, the electrochemical analysis of LSCF-SDC cathode cell is carried out at 650~750°C. The performance improvement of the solid oxide fuel cell at intermediate operating temperature is maximized through the fabrication of the cathode functional layer using the solution infiltration method and the alternative flash light sintering process. Reference [1] J. Hong, A. Bhardwaj, Y. Namgung, H. Bae, S.-J. Song, Evaluation of the effects of nanocatalyst infiltration on the SOFC performance and electrode reaction kinetics using the transmission line model, Journal of Materials Chemistry A, 8 (2020) 23473-23487.[2] J. Shin, S. Yang, H.-I. Ji, S. Park, H. Kim, J.-W. Son, J.-H. Lee, B.-K. Kim, J. Hong, K.J. Yoon, Low-temperature processing technique of Ruddlesden-Popper cathode for high-performance solid oxide fuel cells, Journal of Alloys and Compounds, 868 (2021) 159092.[3] Y. Lim, J. Park, H. Lee, M. Ku, Y.-B. Kim, Rapid fabrication of lanthanum strontium cobalt ferrite (LSCF) with suppression of LSCF/YSZ chemical side reaction via flash light sintering for SOFCs, Nano Energy, 90 (2021) 106524.

Electrochemical Evaluation of Nickel Oxide Addition toward Lanthanum Strontium Cobalt Ferrite Cathode for Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFCS)

A mixture of lanthanum strontium cobalt ferrite (LSCF) and nickel oxide (NiO) makes for a desirable cathode material for an IT-SOFC due to its excellent oxygen reduction capability. This study investigates the effect of NiO addition into LSCF cathode on its physical and electrochemical properties. To optimise the amount of NiO addition, both electrochemical impedance spectra and bode phase were used to examine various weight ratios of nickel oxide and LSCF cathode. Brunauer-Emmett-Teller (BET) and thermal analyses validated the electrochemical observation that the LSCF:NiO ratio yields sensible oxygen reduction reaction and stoichiometric findings. Initial characterisation, comprising of phase and bonding analyses, indicated that LSCF-NiO was successfully synthesised at 800 °C using an improved modified sol gel technique. The addition of 5% nickel oxide to LSCF results in the lowest area specific resistance (ASR) value overall. The Bode phase implies that the addition of 5% nickel oxide to LSCF reduces the impedance at low frequencies by 64.28 percent, indicating that a greater oxygen reduction process happened at the cathode. After the addition of 5 wt% NiO, a single LSCF-NiO cell may function at temperatures as low as 650 °C and the LSCF cathode power density is increased by 25.35%. The surface morphology of the LSCF-NiO cathode reveals that the average particle size is less than 100 nm, and mapping analysis demonstrated a homogenous NiO distribution over the cathode layer. Consequently, the synthesis of LSCF-NiO at intermediate temperatures (800–600 °C) revealed outstanding chemical compatibility, bonding characteristics, and electrochemical performance.

Rapid fabrication of lanthanum strontium cobalt ferrite (LSCF) with suppression of LSCF/YSZ chemical side reaction via flash light sintering for SOFCs

The chemical side reaction between a lanthanum strontium cobalt ferrite (LSCF) cathode and an yttria-stabilized zirconia (YSZ) electrolyte is a key problem for solid oxide fuel cell (SOFC) fabrication. Herein, we demonstrate rapid fabrication of an LSCF cathode using a novel flash light sintering (FLS) technique to suppress the chemical side reaction; notably, no Gd-doped ceria interlayer is required. The FLS-fabricated LSCF cathode shows comparable crystalline development and microstructural evolution to a cathode fabricated using the conventional high-temperature sintering process. A clear LSCF/YSZ interface appears, indicating suppression of detrimental chemical side reactions via rapid and surface-dominant sintering kinetics. Detailed interfacial microstructure analysis reveals the absence of Sr segregation and SrZrO3 formation at the FLS-LSCF cathode/YSZ electrolyte interface. Remarkable performance of 0.9 W cm–2 power density at 750 °C is achieved for a cell incorporating the rapidly fabricated LSCF cathode on the interlayer-free YSZ electrolyte owing to suppression of the insulating secondary phases and significantly reduced polarization resistance. Hence, rapid LSCF cathode fabrication via the novel FLS method effectively suppresses secondary phase formation at the LSCF/YSZ interface and greatly simplifies SOFC fabrication by eliminating the doped-ceria-based interlayer. Moreover, this novel method could help overcome interfacial chemical reaction problems in various solid-state devices, while also providing new application opportunities for high-performance electrolyte/electrode materials.

Lanthanum strontium cobaltite-infiltrated lanthanum strontium cobalt ferrite cathodes fabricated by inkjet printing for high-performance solid oxide fuel cells

Abstract In this study, lanthanum strontium cobalt ferrite cathodes surface-treated with lanthanum strontium cobaltite nanoparticles are synthesized using inkjet printing and their performances are evaluated using intermediate-temperature solid oxide fuel cells. The porous lanthanum strontium cobalt ferrite cathode of an anode-support solid oxide fuel cell is prepared under optimized inkjet printing conditions. The surface treatment is performed by infiltrating a lanthanum strontium cobaltite ink followed by calcination. The lanthanum strontium cobalt ferrite cathode is evenly surface-covered with lanthanum strontium cobaltite nanoparticles, confirming the effectiveness of the inkjet printing for the cathode surface modification. The fuel cell performances are evaluated in the intermediate temperature range of 550–650 °C. The power is significantly improved even with a small addition of the surface lanthanum strontium cobaltite; the enhancement factor reaches the value of five. An electrochemical impedance analysis confirms that the enhanced fuel cell performance is attributed to the reduced polarization impedance, significantly activating the surface catalysis. The addition of lanthanum strontium cobaltite retained the stability of the lanthanum strontium cobalt ferrite cell. However, an excessive amount of lanthanum strontium cobaltite significantly reduces the cell performance.

Experimental Optimization of Ni-GDC Microstructure with Various Phase Fractions for Solid Oxide Fuel Cell Anode

The design of electrode microstructure is important to enhance performance and stability of solid oxide fuel cells (SOFCs). The most common material used for the fuel electrode is nickel-yttria stabilized zirconia (Ni-YSZ) composite, in which electron, ion and gas conduct in the metallic Ni phase, the ceramic YSZ phase and the pores, respectively. The electrochemical reaction therefore takes place at the triple-phase-boundary (TPB), hence the increase in TPB density improves electrode performance. Recently, the ceramic materials, which exhibits mixed ionic-electronic conductivity (MIEC) properties, are considered to be beneficial solution for the SOFC electrodes. They can greatly enhance the available reaction sites by introducing surface reactions on the double phase boundaries (DPB) between MIEC phase and pore. One of the promising materials is considered to be gadolinium doped ceria (GDC). GDC exhibits higher ionic conductivity compared to YSZ and has MIEC property in the reducing atmosphere. In the case of Ni-GDC composites, the electrochemical performance is supported by both DPB and TPB reactions. In general, the active DPB density increases with the share of GDC phase in the composite. On the other hand, the active TPB density achieves maximum value when the share of both solid phases is balanced. The optimal electrode design has to be determined by the ratio between DPB and TPB reactions and their kinetics. In the present study, electrolyte supported SOFC with Ni-Gd0.1Ce0.9O2-δ anodes with various phase fractions were fabricated and their polarization characteristics were experimentally investigated. The ratio of Ni and GDC was controlled by the initial powder composition, and the porosity was varied by isostatically pressing the anode after screen printing. Initially, NiO (AGC Seimi) and GDC (ShinEtsu) powders were mixed to achieve the target volume fractions of Ni:GDC = 70:30, 60:40, 50:50, 40:60, 30:70 vol%. The anodes were then screen-printed on the YSZ discs and calcinated at 1350oC. In order to modify the porosity of the anodes, some of the cells undergoes isostatic pressing treatment at 200 MPa for 30 minutes prior to the calcination. The LSCF (lanthanum strontium cobalt ferrite by Fuel Cell Materials) cathode with GDC (ShinEtsu) barrier layer were screen-printed and sintered on the other side of the electrolyte. Current – voltage curves and electrochemical impedance spectra were measured at 500 – 800 oC. Additionally, the anodes with optimal phase composition were discharged for 100 hrs. 3D microstructural analysis was conducted with the focused ion beam scanning electron microscopy (FIB-SEM). The microstructural parameters, such as phase volume fractions, particle intercept length, TPB and DPB densities and tortuosity factors were quantified. By evaluating the connectivity of each phase, the total and active TPB and DBP densities were calculated. Quantified microstructural parameters were correlated with the polarization characteristics. Neither the DPB reactions nor the TPB reactions could individually explain the measured polarization resistances of the composite anodes. In the case of screen-printed anode samples without isostatic pressing, the high porosity (ca. 52% for all of the samples) lead to low connectivity of the solid phases. The optimal composition of the cermet was found to be Ni:GDC = 0.4:0.6 vol%. Introducing isostatic pressing, improvements in both ohmic and polarization resistances are observed. The decrease in ohmic resistance is mainly attributed to the improved connectivity between the electrode and the electrolyte. The polarization resistance was influenced by the changes in active DPB and TPB densities. As the porosity is reduced and connectivities of the solid phases are enhanced by the isostatic pressing, not only the nominal values of active DPB and TPB densities increased, but also the ratio between them has changed. This effect is most significant for Ni:GDC = 0.3:0.7 vol% sample, which exhibits the smallest polarization resistance among all the investigated electrodes. The discharge testing showed the improved stability of the cells with the decreased porosity. It is therefore concluded that not only the ratio between Ni and GDC but also porosity is a very important parameter for the performance and stability of the anode. Figure 1

Au-Coated Lanthanum Strontium Cobalt Ferrite Cathode for Lowering Sheet Resistance of a Solid Oxide Fuel Cell

In this paper, we fabricate a thin film solid oxide fuel cell (SOFC) with a lanthanum strontium cobalt ferrite (LSCF) cathode which is coated with an Au layer by sputtering. The fabricated thin film SOFC has a 370-nm-thick Ni anode/880-nm-thick YSZ electrolyte/440-nm-thick LSCF cathode/130-nm-thick Au layer. The electrochemical performances of the thin film SOFC with the LSCF cathode coated with a 130-nm-thick Au layer and another SOFC without an Au layer are measured at the operating temperature of 600 °C. Since the LSCF cathode coated with a 130-nm-thick Au layer significantly lowers the sheet resistance (in-plane direction resistance), the peak power densities of the thin film SOFC with the LSCF cathode coated with a 130-nm-thick Au layer and the thin film SOFC with the LSCF cathode without a 130-nm-thick Au layer are 500 mW/cm2 and 49 mW/cm2, respectively. Due to the LSCF cathode coated with a 130-nm-thick Au layer, the peak power density of the thin film SOFC with the Au-coated LSCF cathode is 10 times higher than that of the LSCF cathode without Au layer.

Composite cathode material LSCF-Ag for solid oxide fuel cells obtained in one step sintering procedure

The lanthanum strontium cobalt ferrite (LSCF)-Ag composite cathode material was prepared in aqueous solution by new one-step method. In this method silver nanoparticles obtained by the reduction of [Ag(NH3)2]+ complex with sucrose were directly deposited onto the surface of LSCF powder. UV–Vis spectra of supernatant solution taken during synthesis showed the presence of a sharp excitation band near 397 nm attributed to the surface plasmon excitation of silver nanoparticles. Obtained composite powder was sintered to samaria doped ceria electrolyte in one step sintering procedure at 1000 °C. The presence of silver in LSCF cathode facilitates the oxygen reduction. The comparison of impedance spectra of LSCF-Ag cathodes with spectra reported in literature for similar LSCF cathodes shows that this effect is important at lower oxygen partial pressures. The analysis of the electrochemical impedance spectra recorded in the range 10−2–1010 Hz reveals that the second high frequency semicircle ascribed to the electrolyte grain boundary impedance is distorted due to process belonging to oxygen reduction reaction.

Effect of NiO addition on oxygen reduction reaction at lanthanum strontium cobalt ferrite cathode for solid oxide fuel cell

Lanthanum strontium cobalt ferrite (LSCF), a perovskite's family member, has gained much attention as the electrocatalyst for the oxygen reduction reaction (ORR) in intermediate temperature solid oxide fuel cells. However, it still needs a strategy to improve its catalytic activity. In this work, NiO is primarily investigated as a possible synergistic catalyst for ORR on the LSCF surface. The effect of NiO particles on the effective oxygen chemical surface exchange coefficient is revealed with the electrical conductivity relaxation (ECR) technique. At 800 °C, the coefficient is increased from 3.48 × 10−5 to 6.65 × 10−5 cm s−1 and 6.9 × 10−4 cm s−1 when NiO particles are deposited using the sputter and drop coating methods, respectively. Adding 5 wt % NiO to LSCF reduces the area specific interfacial polarization resistance, for example from 0.108 to 0.082 Ω cm2 at 700 °C, as demonstrated by impedance spectroscopy on symmetric cells using samaria-doped ceria as the electrolyte. Adding NiO can also improve the performance of anode supported button cells, increasing the peak power density from 0.731 to 1.031 W cm−2 at 800 °C. On the whole, the increased oxygen surface exchange rate together with the reduced electrode resistance and improved power density, exhibit that NiO is a potential additive to enhance the LSCF catalytic activity.

CaO effect on the electrochemical performance of lanthanum strontium cobalt ferrite cathode for intermediate-temperature solid oxide fuel cell

The oxygen reduction reaction (ORR) on lanthanum strontium cobalt ferrite (LSCF) catalyst is critical for intermediate temperature solid oxide fuel cells (SOFCs). The reaction rate can be effectively improved by addition various nanoparticles including electrocatalysts such as Pd, Ag and mixed electronic-ionic conductors and electrolytes like samaria doped ceria (SDC). This work shows that ORR rate can also be improved by CaO, which is neither catalyst nor conductor. The CaO nanoparticles are deposited to porous LSCF electrodes using the infiltrating technique. No obvious reaction between CaO and LSCF is detected with X-ray diffraction analysis, indicating that CaO is chemically compatible with LSCF in the intermediate-temperature SOFC operation conditions. Impedance spectrum analysis demonstrates that the CaO nanoparticles can effectively reduce the interfacial polarization resistances for both single phase LSCF electrodes and LSCF-SDC composite electrodes. In addition, CaO nanoparticles can improve the peak power densities and reduce the total electrode resistances of single cells consisting of NiO-SDC anodes, SDC electrolytes, and LSCF based cathodes. Further, CaO can increase the oxygen surface exchange coefficient as demonstrated with electrical conductivity relaxation measurement. The improving factor is comparable to those for Rh and Pd catalysts, suggesting it is effective to increase ORR rate by infiltrating CaO nanoparticles.

High conductive (LiNaK)2CO3[sbnd]Ce0.85Sm0.15O2 electrolyte compositions for IT-SOFC applications

Composite electrolytes of lithium, sodium, and potassium carbonate ((LiNaK)2CO3), and samarium doped ceria (SDC) have been synthesized and the carbonate content optimized to study conductivity and its performance in intermediate-temperature solid oxide fuel cell (IT-SOFC). Electrolyte compositions of 20, 25, 30, 35, 45 wt% (LiNaK)2CO3–SDC are fabricated and the physical and electrochemical characterization is carried out using X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscope, and current–voltage measurements. The ionic conductivity of (LiNaK)2CO3–SDC electrolytes increases with increasing carbonate content. The best ionic conductivity is obtained for 45 wt% (LiNaK)2CO3–SDC composite electrolyte (0.72 S cm−1 at 600 °C) followed by the 35 wt% (LiNaK)2CO3–SDC composite electrolyte (0.55 S cm−1 at 600 °C). The symmetrical cell of the 35 wt% (LiNaK)2CO3–SDC composite electrolyte with lanthanum strontium cobalt ferrite (LSCF) electrode in air gives an area specific resistance of 0.155 Ω cm2 at 500 °C. The maximum power density of the fuel cell using 35 wt% (LiNaK)2CO3–SDC composite electrolyte, composite NiO anode and composite LSCF cathode is found to be 801 mW cm−2 at 550 °C.

A 2D and 3D X-ray μ-diffraction and μ-fluorescence study of a mixed ionic electronic conductor

Due to the mixed ionic electronic conductive properties of the Lanthanum Strontium Cobalt Ferrite (LSCF) La0.6Sr0.4Co0.2Fe0.8O3−δ compound, it is of great scientific and technological interest. Especially in the Solid Oxide Fuel Cell (SOFC) technology, this compound has receiving great attention as a cathode material. However, its chemical reactivity with the Yttria-stabilized Zirconia (YSZ) electrolyte still remains one of the main challenges, which demands a comprehension in the μm and sub-μm range. In order to address the reactivity issues locally in the micrometre scale range, 2D and 3D X-ray μ-diffraction and μ-fluorescence analysis have been performed on a pristine LSCF cathode layer. The cathode was deposited on a dense YSZ electrolyte substrate spaced by a thin Gadolinium doped Ceria Oxide (CGO) barrier layer in between LSCF and YSZ to limit the reactivity. The present approach offers a larger field of view in comparison to electron microscopy techniques. The method can provide a more representative information and may offer some insights on the reactivity distribution along the interfaces. The formation of micro SrZrO3 inclusions in LSCF layer is then indubitably identified, as well as in the CGO/YSZ interface.

An Operando Fluorescence XAS Study of a Ni/YSZ Anode in a Solid Oxide Fuel Cell

Introduction Solid oxide fuel cells (SOFC) have high energy conversion efficiencies because of their ability to directly convert the chemical energy stored in fuels into electrical energy. Ni/YSZ (yttria-stabilized zirconia) cermet is commonly used for SOFC anodes, because Ni provides excellent catalytic activity and current collectability and YSZ provides good ionic conductivity and structural support. However, Ni/YSZ facies several problems such as instability upon redox cycling, nickel coarsening, carbon deposition and so on. Therefore, designing anode materials with high durability is a key objective in the development of SOFC technology. Especially, it is essential to understand the redox behavior of the Ni electrocatalysts at work. Operando X-ray absorption spectroscopy (XAS) is a powerful tool to investigate the relationship between the oxidation state of active site and cell performance under an operating condition. Hence in this work, we developed an operando fluorescence XAS measurement system for SOFC to study the oxidation state of the working Ni electrocatalyst at temperatures ranging from 973 to 1073 K. Experimental Figure 1a depicts a two-chamber SOFC for operando fluorescence XAS measurement developed in the present work. An anode-supported cell having a groove for the investigation of the interfacial region between the Ni/YSZ anode and the YSZ electrolyte was installed to the operando XAS measurement system. The lidded XAS instrument was heated up to 1073 K in the air to melt the seal material (Pyrex glass), and subsequently NiO in the anode was reduced in a gas flow consisting of 4% H2, 3% H2O, and N2 balance. After completing gas seal and NiO reduction, the reactor temperature was lowered to 973 K for operation. The Ni K-edge XAS measurement was implemented at the BL33XU (the Toyota beamline) of SPring-8 in fluorescence mode by irradiating the bottom center of the groove at the anode and detecting the emitted X-ray with a four-element silicon drift detector. The anode potential was measured or adjusted with reference to the potential of lanthanum strontium cobalt ferrite cathode. Results The operando XAS technique was applied to the reduction of NiO at the Ni/YSZ anode at 1073 K. Figure 1b shows a chronopotentiogram of the Ni/YSZ anode and corresponding change in average Ni valence estimated by the height of the main peak at the Ni K-edge. The average Ni valence and the anode potential exhibited different changing trends in the reduction process. There seemed to exist four regions for anode potential (i.e., two potential transition and two plateau regions) and two regions for average Ni valence. In situ observation with a CCD camera clarified that the reduction of NiO around the anode–electrolyte interface started in region 2 and continued until region 4. Operando XAS measurement was also conducted to examine the oxidation state of Ni in a high-power operation at 973 K. As a time-averaged oxidation state, Ni at the Ni/YSZ anode kept its metallic state even though the anode potential was so high as −0.4 V. The oxidation behavior of Ni at the anode as mentioned above and its relationship with degradation in the high-power operation will be further discussed in the conference. Acknowledgements The authors are grateful to Prof. Koji Amezawa of Tohoku University for his fruitful advices and discussion on the development of the operando fluorescence XAS measurement system for SOFC. All the XAFS measurements were performed at the BL33XU (the Toyota beamline) of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) with the proposal numbers of 2014B7024, 2015A7024, and 2015B7024. Figure 1

Fabrication of lanthanum strontium cobalt ferrite (LSCF) cathodes for high performance solid oxide fuel cells using a low price commercial inkjet printer

In this study, we investigate a method to fabricate high quality lanthanum strontium cobalt ferrite (LSCF) cathodes for solid oxide fuel cells (SOFCs) using a commercial low price inkjet printer. The ink source is synthesized by dissolving the LSCF nanopowder in a water-based solvent with a proper amount of surfactants. Microstructures of the LSCF layer, including porosity and thickness per printing scan cycle, are adjusted by grayscale in the printing image. It is successfully demonstrated that anode-supported SOFCs with optimally printed LSCF cathodes can produce decent power output, i.e., a maximum peak power density of 377 mW cm−2 at 600 °C, in our experiment. We expect that this approach can support the quick and easy prototyping and evaluating of a variety of cathode materials in SOFC research.

Degradation Studies and Sr Diffusion Behaviour in Anode Supported Cell after 3,000 h SOFC Short Stack Testing

Solid Oxide Fuel Cells (SOFCs) are promising candidates for future energy conversion devices that transform chemical energy of fuel into electricity [1]. One of the main challenges in improving the performance and cost-effectiveness of SOFC is the control of the degradation processes, such as Sr diffusion and chemical interactions which can contribute to the overall reduction of the cell performance [2-4]. Several authors have evaluated the importance of cation diffusivities for surface segregation of Sr and thus for a major degradation mechanism of SOFC cathodes [5, 6]. In the present work, a 3000 hour degradation test was carried out at 780 ºC in a short stack under real time operation conditions. After the test, a cell from this stack was disassembled and samples from nine different areas were analyzed, looking for evidences of degradation phenomena taking place. A pristine sample was also analysed as reference. The stack consist on coated ferritic stainless steel, anode supported cells and seal. The cells are supportend on a Ni-YSZ cermet anode with yttria-stabilized zirconia (YSZ) as electrolyte and a lanthanum strontium cobalt ferrite (LSCF) oxide as cathode material. A gadolinia-doped ceria (GDC) is used as barrier layer between cathode and electrolyte to prevent the formation of poorly conducting secondary phases, such as SrZrO3 or La2Zr2O7[7]. The aim of this work is to study the Sr diffusion, the effectiveness of GDC barrier layer and the evolution of LSCF cathode during operation. The deterioration of the performance measured in the cell is correlated with degradation mechanisms observed in post mortem experiments carried out in pristine and aged cells. The evolution of the Sr and other species in the cathode is examined by X-ray diffraction (XRD), confocal laser Raman spectroscopy, electron probe micro analyzer (EPMA-WDS), scanning electron microscopy equipped with an Energy-dispersive X-ray analyzer. Besides, the concentrations of pollutants in cells were obtained by inductively coupled plasma optical emission spectrometry (ICP-OES) after dissolution in acid. A local microstructural and phase distribution study is carried out by means of transmission electron microscopy (TEM) and a high resolution scanning electron microscope coupled with electron energy-loss spectroscopy (EELS). The results throw light on the evolution of the cathode/barrier layer/electrolyte system of SOFC cells working under real conditions after long operating time (Figure 1). Figure 1. SEM images of the cross section and EPMA elemental distribution maps of the LSCF/GDC/YSZ in pristine and aged cells.

Effect of nanostructured anode functional layer thickness on the solid-oxide fuel cell performance in the intermediate temperature

Effect of anode functional layer thickness on the performance of solid-oxide fuel cells (SOFCs) has been investigated in the intermediate temperatures of 600–650 °C. Three types of cells with different thickness (0, 4, 10 micron) of nanostructured anode functional layer (AFL) consisting of Ni-ScSZ (Scandia stabilized zirconia) are prepared. The SOFCs consist of Ni-3YSZ (3 mol% yttria stabilized zirconia) anode tube support with the AFL, ScSZ electrolyte, and LSCF (lanthanum strontium cobalt ferrite) and GDC (gadolinium doped ceria) mixture cathode. It is shown that the performance of the cell is improved as the thickness of the anode functional layer increases. Power densities of the cell with 10 micron thick AFL at 600 and 650 °C are shown to be 0.22 and 0.27 W/cm2 at 0.75 V, respectively. According to impedance spectroscopy, improvement of both ohmic and polarization resistances has been observed by increasing the thickness of the AFL, suggesting that the AFL also acts as a better contact layer between the electrolyte and the anode support, and the effectiveness of the AFL by optimizing the thickness.

Long-Term SOFCs Button Cell Testing

This paper reports a new study where relatively long-term tests of about a 1000 h are performed on several planar anode-supported solid oxide fuel cells. The cell electrochemical behaviors are studied by using voltage-current density measurement, electrochemical impedance spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The cell total polarization obtained from electrochemical impedance spectroscopy results is shown to be consistent with the area-specific resistance calculated from the voltage-current density curve over the course of the test. In addition, a four-constant phase element model is used to analyze the cell components resistances at different intervals over the lifetime of the test. Scanning electron microscopy and energy-dispersive X-ray spectroscopy are used postmortem to determine if any damages occurred to the cells and to determine if any change in composition occurred to the lanthanum strontium cobalt ferrite cathode. This study shows that the tested cells remain stable with a relatively small increase in the cell total polarization but with no increase in ohmic resistance.

Influence of wet atmosphere on electrical and transport properties of lanthanum strontium cobalt ferrite cathode materials for protonic ceramic fuel cells

Abstract Lanthanum strontium cobalt iron oxide (LSCF) is a mixed ionic and electronic conducting cathode material used in solid oxide fuel cells (SOFCs) and protonic ceramic fuel cells (PCFCs). However, owing to the lack of understanding of LSCF materials' electrical and transport properties under actual PCFC operating conditions, the general criterion that can determine whether LSCF can be applied to PCFC cathodes has yet to be determined. In this study, the influence of wet atmosphere on the electrical and transport properties of an LSCF cathode was investigated. After changing the gas from dry air to wet air, the electrical conductivity of the LSCF cathode measured via the DC four-probe method increases very slowly, and it reaches a saturated value after about 120 h. The chemical diffusivity ( D chem ) measured via the conductivity relaxation technique also decreases to log D chem = − 6.15 ± 0.01 (cm 2 s − 1 ) after the LSCF cathode is exposed to wet atmosphere, which is one order of magnitude lower than that of log D chem = − 4.91 ± 0.01 measured in dry atmosphere. In the conductivity relaxation experiment, all the relaxation characteristics during a cycle of changes in water vapor activity are found to be caused by oxygen diffusion rather than proton diffusion. Using XPS depth profiling, we demonstrate that the reduction in D chem and its related sluggish conductivity relaxation in wet atmosphere are caused by the compositional change in the region approximately 100 nm away from the LSCF surface.

Nanostructured ceria based thin films (≤1 μm) As cathode/electrolyte interfaces

Gadolinium doped cerium oxide (CGO: Ce0,9Gd0,1O2−δ) films were used as an oxygen anion diffusion layer at the cathode/electrolyte interface of Solid Oxide Fuel Cells (SOFCs), between LSCF (lanthanum strontium cobalt ferrite) and YSZ (yttria-stabilized zirconia).Thin (∼100nm) and thick (∼700nm) mesoporous CGO layers were synthesized through a sol–gel process including organic template coupled with the dip-coating method. Structural and microstructural characterizations were performed, highlighting a well-bonded crystalline CGO nanoparticles network which delineates a 3-D inter-connected mesoporous network. Their electrical behaviors were investigated by impedance spectroscopy analysis of YSZ/mesoporous-CGO/LSCF half-cell. Anode-supported SOFCs, operating at 800°C, with either dense or mesoporous CGO dip-coated interlayers were also fabricated [NiO-YSZ anode/YSZ/CGO/LSCF cathode]. The impact of the mesoporous CGO interlayers on SOFCs performances was investigated by galvanostatic analysis and compared to the behavior of a dense CGO interlayer.The polarization curves revealed an enhancement in the electrical performance of the cell, which is assigned to a decrease of the polarization resistance at the cathode/electrolyte interface. The integrity and connectivity of the CGO nanoparticles bonded network facilitates O2− transport across the interface.

Design and Preparation of SOFC Unit Cells Using Scandia-Stabilized Zirconia Electrolyte for Intermediate Temperature Operation

A solid oxide fuel cell unit cell based on a scandia-stabilized zirconia (ScSZ) electrolyte for intermediate temperature operation (below 650°C) was manufactured as an anode-supported unit cell via uniaxial pressing, dip-coating, and screen printing methods. The nanocomposite powders used to improve anode performance were synthesized by selectively coating nanosized NiO particles on ScSZ core particles by the Pechini process. Anode-supported ScSZ electrolytes were fabricated by dip-coating a slurry of Ni-ScSZ composite powder on a die-pressed anode pellet, followed by dip-coating of the electrolyte ScSZ slurry. The lanthanum strontium manganite (LSM)-ScSZ cathode and the samarium doped ceria (SDC) interlayer were formed on the anode-supported ScSZ electrolyte using the screen printing method. The lanthanum strontium cobalt ferrite (LSCF)–SDC cathode was also formed on the SDC interlayer. The anode-supported unit cells designed and prepared in this study had a power density of 0.61 W cm−2 at 800°C. Moreover, the unit cell structured by the functional layer and the LSCF cathode demonstrated excellent performance with a power density of 0.49 W cm−2 at 650°C.