LSGM Electrolyte Research Articles

Evaluation of GdSrCoO4+δ intergrowth oxides as cathode materials for intermediate-temperature solid oxide fuel cells

This paper reports on synthesis and evaluation of an intergrowth oxide, GdSrCoO4+δ (GSCO), as a new cathode material for intermediate-temperature solid oxide fuel cells. The oxygen content and the thermal expansion coefficient of GSCO oxide powders were measured. The GSCO oxide shows a semi-conducting behaviour in air with conductivities increasing from 16 S cm−1 at 500°C to 65 S cm−1 at 800°C. The catalytic activities of GSCO oxides for oxygen reduction reactions are evaluated using symmetrical impregnated GdSrCoO4+δ–La0.9Sr0.1Ga0.8Mg0.2O3 (GSCO-LSGM) cathode fuel cells. The polarization resistances for such composites increase from 0.072Ω cm2 at 650°C to 0.55Ω cm2 at 550°C. Furthermore, thin LSGM electrolyte supported fuel cells with impregnated Ni anodes and GSCO cathodes exibit high power densities at reduced temperatures, e.g., 782 mW cm−2 at 550°C and 1314 mW cm−2 at 650°C, respectively. These results demonstrate that GSCO is a promising cathode candidate for intermediate-temperature solid oxide fuel cells with LSGM electrolytes.

Mechanism and Kinetics of Oxygen Reduction in Porous Nd2NiO4+ δ Electrodes

Solid Oxide Fuel Cells (SOFC) cathodes must exhibit high catalytic activity for oxygen reduction, as well as good thermal and chemical compatibility with solid electrolytes in order to minimize resistance and promote stabile operation [1]. The Ln2NiO4+δ (Ln = La, Nd, Pr, for example) nickelates, belonging to the Ruddlesden-Popper series, have been proposed as cathode materials. These oxides have the aptitude to accommodate oxygen ions into interstitial sites in the LnOx layer, which gives rise to a high ionic conductivity by interstitial oxygen diffusion [2]. In addition, the Ln2NiO4+δ materials present Thermal Expansion Coefficients (TEC) similar to the most widely used SOFC or IT-SOFC electrolytes: 8mol% Y2O3 stabilized ZrO2 (YSZ), Ce0.9Gd0.1O1.96 (CGO) and La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM) [3-4].In this work, we present a study of the reaction mechanism and the kinetic parameters of porous Nd2NiO4+δelectrodes. Three different microstructures have been obtained using different preparation methods. The conventional Solid State Reaction (SSR) and Pechini methods, and a soft chemical route based on a sol-gel method. Details of these syntheses are described in [5]. These materials have been deposited by spin coating on dense LSGM electrolytes and were fired at 1000°C. The resulting microstructures were quantified by 3D focused ion beam-scanning electron microscope (FIB-SEM) tomography. Figure 1 shows example 2D images from the 3D FIB-SEM data sets showing markedly different microstructures.Electrochemical Impedance Spectroscopy (EIS) was used to measure the cells for temperatures ranging from 600 to 700°C and oxygen partial pressures (pO2) between 1 atm and 6∙10-4 atm in order to identify possible rate-limiting steps of the oxygen reduction reaction. The EIS spectra, which showed a low and a high frequency response, were fit using an electrical equivalent circuit model composed of two elements – the high frequency contribution was fit using a Gerischer-type element, whereas a parallel resistor/capacitor (RC) element was used for the low frequency arc. The low frequency contribution was only detected at low pO2 and temperatures, with its size increasing with increasing particle size. The Gerischer element suggests a co-limitation by surface exchange kinetics and oxygen diffusion. The variation of the resistance (RG) and relaxation time (τG) of the Gerischer-type contribution are plotted in Figure 2.The 3D FIB-SEM data (porosity, specific surface area, tortuosity) was used in the ALS model [6] to find the characteristic kinetic parameters, oxygen surface exchange (k) and oxygen chemical diffusion coefficient (Dchem) that correctly predict the EIS-measured RG and τG values. The results will be compared with reported values for Nd2NiO4+δ. Note that the main change in microstructure, the changes in particle size and specific surface area (Fig. 1), agree with the measured RG values according to the ALS model. That is, high surface area (smaller particle size) led to lower RG. The microstructure plays an important role in determining the mechanism of the reaction. Thus, the lower pO2 dependence for RG and τG and the high polarization resistance suggest that the kinetics of the oxygen reduction reaction is mainly limited by a bulk transport path for the SSR sample.

Investigations on structural and electrical properties of calcium substituted LSGM electrolyte materials for IT-SOFC

Strontium and magnesium doped lanthanum gallate, La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM) and a few compositions of calcia (CaO) incorporated LSGM, La(0.9−x)CaxSr0.1Ga0.8Mg0.2O2.85; x≤0.10, were prepared by conventional solid state ceramic route. The X-ray diffraction patterns showed orthorhombic LSGM phase along with a few impure secondary phases. SEM micrograph depicted fairly dense grain morphology of the system. The textural properties were also found to be quite suitable for solid oxide fuel cell electrolyte applications. The electrical conductivity of the systems was measured in the frequency range 20Hz to 1MHz and temperature range 300–800°C. The total conductivity of the system was found to first increase up to x=0.05 and thereafter it decreased for higher concentrations of the dopant. A small amount of calcia (upto x=0.05) scavenges the intergranular secondary impure phases resulting in a significant increase in grainboundary conduction. The presence of extra secondary phases in the higher compositions has been attributed to decrease in electrical conductivity.

MoO3 nanorods/Fe2(MoO4)3 nanoparticles composite anode for solid oxide fuel cells

MoO3 nanorods/Fe2(MoO4)3 nanoparticles composite has been prepared by a hydrothermal method combined with an in situ diffusion growth process. Single cells based on 300 μm LSGM electrolyte have been fabricated with the MoO3 nanorods/Fe2(MoO4)3 nanoparticles composite anode and a composite cathode consisting of Sr0.9Ce0.1CoO3−δ and Sm-doped ceria (SDC). The peak power densities reach 225, 50, 75 mW cm−2 at 900 °C in H2, CH4 and C3H8, respectively. The cell shows excellent long-term stability at 850 °C. The preliminary results demonstrate that the MoO3 nanorods/Fe2(MoO4)3 nanoparticles composite is a promising alternative anode for solid oxide fuel cells.

Decreased sintering temperature of anode-supported solid oxide fuel cells with La-doped CeO2 and Sr- and Mg-doped LaGaO3 films by Co addition

Effects of decrease in sintering temperature (1473–1623 K) on the electrochemical performance of anode-supported solid oxide fuel cells (SOFCs) were investigated using Sr- and Mg-doped LaGaO3 (LSGM) electrolyte film while using La-doped CeO2 with Co addition (Co–LDC) as the buffer layer. The sintering temperature of the single cell was reduced to 1523 K by the use of Co–LDC buffer layer. The cell showed maximum power density (MPD) of ∼1 W cm−2 and an open circuit voltage (OCV) close to the theoretical value at 973 K, which was comparable with previous results for cells prepared by sintering at 1673 K. The cell performance was further improved with increasing the sintering temperature because of the reduced internal resistances, and it was stable after operation for 92 h at 973 K, suggesting that the Co–LDC buffer layer posed no detrimental effect. Thus, Co–LDC is a promising buffer layer for LSGM electrolyte film prepared by wet coating and cosintering processes to improve the performance of anode-supported SOFCs.

Electrical conductivity of barium substituted LSGM electrolyte materials for IT-SOFC

Strontium and magnesium doped lanthanum gallate, La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM), and Ba-incorporated LSGM with compositions La0.9−xBaxSr0.1Ga0.8Mg0.2O2.85;x≤0.15 (LBSGM) were prepared by conventional solid state route. The X-ray diffraction patterns of the LBSGM system showed the main orthorhombic LSGM phases along with a few impure secondary phases. SEM micrographs exhibited fairly densed grain morphology of the system. The XPS spectra of the system indicated the presence of the constituent elements. It was found that sintered samples are stable in air and the constituent elements were found to exist in their characteristic valence states. The electrical conductivity of the LBSGM system was measured in the frequency range 20Hz to 1MHz and a temperature range of 300–800°C. The electrical conductivity of the system was found to increase slightly first up to x=0.07 and thereafter it decreased for higher dopant concentrations. The formation of additional Ba-derived secondary phases in the compositions with x>0.07 may lead to a decrease in electrical conductivity.

Anode-Supported LSGM Films Prepared by Slurry Spin Coating

La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM) electrolyte films were successfully prepared by slurry spin coating method on porous La0.7Sr0.3Cr0.5Mn0.5O2.75 (LSCM) anode substrates. Ethyl celluloses content, coating cycles for slurry spin coating on the fabrication LSGM electrolyte films were investigated. The compatibility between LSGM and LSCM powders, microstructures and electricity conductivity of fabricated LSGM films were examined using XRD, SEM and electrochemical workstation. The film with good apparent morphology and electrical conductivity were obtained when the operating parameters were setted as the content of ethyl cellulose 10wt%, and the coating cycles 5.

Cobalt-free perovskite cathode materials SrFe1−xTixO3−δ and performance optimization for intermediate-temperature solid oxide fuel cells

Fe-based perovskite oxides SrFe1-xTixO3-δ (SFT, x=0.00–0.15) are developed as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Dense single-phase SFT solid solutions are obtained by sintering the samples at 1300°C for 10h. The SFT materials are chemically compatible with the La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) and Ce0.8Sm0.2O1.9 (SDC) electrolytes at 1000°C for 2h. The highest electrical conductivity of 72 S cm−1 at 650°C in air is obtained for the x=0.05 sample. The substitution of Ti for Fe significantly reduces the thermal expansion coefficients (TECs) from 26.5×10−6K−1 at x=0.00 to 22.9×10−6K−1 at x=0.15 between 30 and 1000°C. Single cells that use SFT as cathodes with x=0.00, 0.05, 0.10, and 0.15 on a 300μm-thick LSGM electrolyte reach the peak power density of 446, 475, 439, and 432 mW cm−2 at 800°C, respectively. The addition of SDC in x=0.05 cathode significantly enhances the cell performance and reduces the TEC of the SFT–SDC composite cathodes. The Ti-substituted SFT perovskites and SFT–SDC composites can be considered cheaper alternative cathode materials for use in IT-SOFCs.

Growth of Thin-Film Layered Perovskite Cathodes by Pulsed Laser Deposition and their Electrochemical Studies in IT-SOFCs

Layered perovskites have attracted abundant interest as advanced cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) due to their high electrical conductivity and excellent catalytic properties for the oxygen reduction reaction (ORR). However, cobalt related layer perovskite oxides generally suffer from larger thermal expansion co-efficiency (TEC) than that of electrolyte materials. In this study, we have prepared a thin interlayer, SmBa0.5Sr0.5Co2O5+δ (SBSCO) layered perovskite, via pulsed laser deposition (PLD) on a Sr- and Mg- doped LaGaO3 (LSGM) thin film electrolyte to prevent the formation of a micro-gap arising from the thermal mismatch between the SBSCO cathode and LSGM electrolyte. A Samaria-doped ceria (SDC) buffer layer was prepared between the cathodic interlayer and LSGM electrolyte in order to prevent interdiffusion of cations. The cathodic interlayer of SBSCO is helpful for overcoming the thermal mismatch between the SBSCO powder cathode and the LSGM electrolyte, and also shows high power generating properties and small area specific resistance under typical fuel cell operating conditions.

Determination of Electrode Oxygen Transport Kinetics Using Electrochemical Impedance Spectroscopy Combined with Three-Dimensional Microstructure Measurement: Application to Nd2NiO4+δ

Oxygen reduction kinetic parameters – oxygen ion diffusion Dδ, molar surface exchange rate ℜO and surface exchange coefficient k – were determined for porous Nd2NiO4+δ solid oxide fuel cell cathodes as a function of temperature and oxygen partial pressure by analyzing electrochemical impedance spectroscopy data using the Adler-Lane-Steele model. Electrode microstructural data used in the model calculations were obtained by three-dimensional focused ion beam-scanning electron microscope tomography. Cathodes were fabricated using Nd2NiO4+δ powder derived from a sol-gel method and were tested as symmetrical cells with LSGM electrolytes. The oxygen surface exchange rate exhibited a power-law dependency with oxygen partial pressure, whereas the oxygen diffusivity values obtained varied only slightly. The present analysis suggests that the O-interstitial diffusion has a bulk transport path, whereas the surface exchange process involves dissociative adsorption on surface sites followed by O-incorporation. For Nd2NiO4+δ at 700°C and 0.2 atm oxygen pressure, Dδ = 5.6·10−8 cm2s−1, ℜO = 2.5·10−8 mol·cm−2 s−1. The present Dδ and ℜO values and their activation energies are slightly different to those previously reported for Nd2NiO4+δ using other measurement methodologies, and lower than typical state-of-the-art Co-rich perovskites. However, the average kδ = 1.0 10−5 cm·s−1 at 700°C is comparable to those of fast oxygen exchange rate perovskites.

Effects of transition metal addition on sintering and electrical conductivity of La-doped CeO2 as buffer layer for doped LaGaO3 electrolyte film

Abstract Effects of transition metal additives (0.5 at.% Fe, Mn, and Co) on densification, microstructure, crystal structure, and electrical conductivity of Ce 0.6 La 0.4 O 2 (LDC) were investigated. The power generation property of a single cell using LDC with the transition metal addition as buffer layer was measured. The addition of Co decreased the sintering temperature of LDC to 1373 K and increased the grain size when the sintering was performed at 1623 K. No impurity phase appeared by the addition of transition metals. The total conductivity of the Co-LDC sample sintered at 1373 K was even higher than that of LDC sintered at 1623 K, and Co-LDC sintered at 1623 K exhibited a conductivity of around 0.01 S cm − 1 at 973 K for the high density and large grain size. The single cell using an LSGM electrolyte film and Co-LDC buffer layers showed an open circuit voltage (~ 1.1 V) close to the theoretical value and the maximum power density of 974, 353, and 84 mW cm − 2 at 973, 873, and 773 K, respectively. Thus, Co-LDC is a promising buffer layer for enhanced sintering density and decreasing the ohmic resistance in anode supported SOFCs using LSGM electrolyte films.

Nonstoichiometric (La0.95Sr0.05)xGa0.9Mg0.1O3−δ electrolytes and Ce0.8Nd0.2O1.9–(La0.95Sr0.05)xGa0.9Mg0.1O3−δ composite electrolytes for solid oxide fuel cells

A-site nonstoichiometric electrolytes (La0.95Sr0.05)xGa0.9Mg0.1O3−δ (LSGM, x = 0.97, 1.00, 1.03), and their composites Ce0.8Nd0.2O1.9 (NDC)–LSGM, were synthesized and investigated. The nonstoichiometry efficiently enhanced the total conductivity of LSGM electrolyte, and the A-site deficient composition showed the highest total conductivity above 550 °C (σt,LSGM(x=0.97) = 0.880 S m−1 > σt,LSGM(x=1.03) = 0.808 S m−1 > σt,LSGM(x=1.00) = 0.582 S m−1 at 600 °C). The cubic fluorite and perovskite structures were adopted by all the composites. The LSGM additive significantly promoted the grain growth of the composite electrolyte. The grain boundary conductivities of the composite electrolytes were more or less 5–10 times higher than that of NDC electrolyte at 500 °C. The optimum A-site nonstoichiometry was found to be x = 0.97 in composite electrolytes. This study provides a possible route to design high performance single phase or composite electrolytes for SOFCs.

Fabrication of Solid Oxide Fuel Cells with a Thin (La0.9Sr0.1)0.98(Ga0.8Mg0.2)O3–δ Electrolyte on a Sr0.8La0.2TiO3 Support

AbstractThis paper describes Sr0.8La0.2TiO3 (SLT)‐supported solid oxide fuel cells with a thin (La0.9Sr0.1)0.98Ga0.8Mg0.2O3–δ (LSGM) electrolyte and porous LSGM anode functional layer (AFL). Optimized processing for the SLT support bisque firing, LSGM electrolyte layer co‐firing, and LSGM AFL colloidal composition is presented. Cells without a functional layer yielded a power density of 228 mW cm–2 at 650 °C, while cells with a porous LSGM functional layer yielded a power density of 434 mW cm–2 at 650 °C. Cells with an AFL yielded a higher open circuit voltage, possibly due to reduced Ti diffusion into the electrolyte. Infiltration produced Ni nanoparticles within the support and AFL, which proved crucial for the electrochemical activity of the anode. Power densities increased with increasing Ni loadings, reaching 514 mW cm–2 at 650 °C for 5.1 vol.% Ni loading. Electrochemical impedance spectroscopy analysis indicated that the cell resistance was dominated by the cathode and electrolyte resistance with the anode resistance being relatively small.

Electrochemical Investigation of Composite Nano La0.6Sr0.4Co0.2Fe0.8O3-δ Infiltration into LSGM Scaffold Cathode on LSGM Electrolyte

As a potential intermediate temperature SOFC cathode, a nano La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) infiltrated into a porous La0. 8Sr0. 2Ga0. 8Mg0. 2O3-δ (LSGM) scaffold cathode was evaluated in combination with a LSGM electrolyte. A XRD analysis revealed resistive phases of LaSrGa3O7 and LaSrGaO4 present in the LSCF/LSGM binary system with sintering over 950 oC. To fabricate a nano catalyst infiltrated into the LSGM scaffold cathode, the porous LSGM scaffold is formed at high temperature (1250 oC). Nano catalysts are coated on the scaffold surface using an infiltration technique and fired at 850oC in air. The cathode polarization resistance (Rp) of nano LSCF infiltrated into the LSGM scaffold cathode was 0.02 Ωcm2, 0.11 Ωcm2, and 0.66 Ωcm2 at 800oC, 700oC, and 600oC, respectively. To improve the oxygen reduction reaction, a Pt/LSCM composite solution was infiltrated into the LSGM scaffold cathode. However, the Rp of the nano Pt/LSCM composite infiltrated into the LSGM scaffold cathode was increased to 0.90 Ωcm2 at 700 oC, despite the Pt has higher electrochemical activity for oxygen reduction than LSCF (Rp for LSCM infiltration was 0.317 Ωcm2 at 700oC).

La0.6Sr0.4Fe0.9Mn0.1O3 Oxide Cathode for the High Temperature CO2 Electrolysis Using LSGM Electrolyte

Solid oxide electrolysis cell for reducing CO2 to CO was studied by using a LaGaO3-based (LSGM) electrolyte at elevated temperature (i.e. 973 - 1173 K). Different kinds of oxide were tried as cathodes for CO2 electrolysis. It was found that LaFeO3–based perovskite material (La0.6Sr0.4Fe0.9Mn0.1O3, LSFM) shows higher activity for CO2 electrolysis with a current density of 0.76 A/cm2 at 1.6 V and 1173 K. Doping Sr and Mn to LaFeO3 is effective for improving the cathode activity for CO2 electrolysis under a reducing atmosphere, which consists of 50%CO2, 1%CO/Ar. a cell with the LSFM oxide has a high selectivity for the electrolysis of CO2 to CO.

Reliability of an All Perovskite-Based Solid Oxide Fuel Cell

A solid oxide fuel cell (SOFC) has been manufactured using a Ni-modified perovskite and perovskite-based electrolyte and cathode. The SOFC has been investigated for operation at intermediate temperatures. In this regard, we have first studied the electrical properties of La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) and gadolinia-doped ceria (GDC) electrolytes and afterwards we have investigated the reliability of the Ni-modified La0.6Sr0.4Fe0.8Co0.2O3 based anode operation in combination with LSGM electrolyte and La0.6Sr0.4Fe0.8Co0.2O3 (LSFC) cathode. A 50 h electrochemical test for the SOFC operation under different fuel feed is presented to show the reliability characteristics of such SOFC architecture.

Core-Shell Structured Sr0.88Y0.08TiO3-Ce0.8Sm0.2O1.9 Composite as an Anode for Solid Oxide Fuel Cells Operating with CH4

A porous Sr0.88Y0.08TiO3 (YST)-Ce0.8Sm0.2O1.9 (SDC) composite with a core/shell structure has been prepared with a sol-gel method and evaluated as an alternative anode for solid oxide fuel cells. The single cells were studied with a YST-SDC anode screened on a 300um LSGM electrolyte and a composite cathode consisting of Sr0.90Ce0.10CoO3- d-SDC (30wt%). When CH4 was used as fuel, the peak power density of the single cell reached about 150 mW cm-2 at 900oC. This anode material showed good stability, without obvious degradation after operating in CH4 more than 10 hours. The preliminary results demonstrate that YST coated SDC composite is a promising alternative anode in solid oxide fuel cells with hydrocarbon fuels.

Application of Low Temperature Ceramic Coating Process for SOFC Electrolyte and Electrode Fabrication

Aerosol deposition, ceramic coating process by powder spray at room-temperature under low vacuum, is a promising process for preparation of SOFC cells and stacks’ component to minimize a detrimental reaction during cell production. Moreover, the process has flexibility of microstructure modification from gas-tight dense structure to porous structure with nano-scaled composites on various substrates including Ni-based cermet or even metal-support. In this study, we developed dense electrolyte coating of LSGM electrolyte on Ni-GDC, Ni, and Crofer22APU support, respectively, at room temperature, and achieved maximum power density of 1.31, 0.79, and 0.28 W/cm2 at 750oC, respectively. Nano-structured porous LSCF cathode were also prepared at room-temperature and polarization resistance of 0.11 Ω·cm2 was achieved.

Electrochemical behaviour of an all-perovskite-based intermediate temperature solid oxide fuel cell

A solid oxide fuel cell (SOFC) has been manufactured using a Ni-modified perovskite and perovskite-based electrolyte and cathode. The SOFC has been investigated for operation at intermediate temperatures (800 °C). The electrical properties of La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) perovskite have been compared to gadolinia-doped ceria (GDC) electrolyte. This has allowed to validate the promising properties of the perovskite electrolyte compared to ceria-based ceramic membranes for operation at intermediate temperatures. The reliability of the Ni-modified La0.6Sr0.4Fe0.8Co0.2O3 perovskite-based anode for operation in combination with the LSGM electrolyte and a La0.6Sr0.4Fe0.8Co0.2O3 (LSFC) cathode has been studied. A 50 h electrochemical test for the SOFC operating under different fuel feed compositions is reported. The all-perovskite SOFC shows promising fuel-flexibility characteristics.

Crystal and magnetic structure of the Bi2RuMnO7 pyrochlore: A potential new cathode for solid oxide fuel cells

A new pyrochlore-like phase of composition Bi2RuMnO7 has been prepared as polycrystalline powder, structurally characterized from X-ray diffraction (XRD) and neutron powder diffraction (NPD) data, in complement with magnetic and transport measurements, and finally tested as cathode material for solid-oxide fuel cells (SOFCs). Bi2RuMnO7 pyrochlore is defined in a cubic unit cell with space group Fd-3m; the structural analysis from NPD data unveils a singular feature consisting of a cation disorder of Mn and Bi atoms between A and B positions. This disorder leads to the reduction of Mn4+ at B position to Mn2+ at A position and the oxidation of Bi3+ at A position to Bi5+ at B position. The low-temperature NPD data indicates an antiferromagnetic coupling of two subsets of Mn4+/Ru4+ spins, demonstrating that the magnetic frustration is partially relieved by the random distribution of Mn and Ru over the 16c sites. The obtained compound displays a metallic-like behavior with conductivity values at the SOFCs working temperatures (650–850 °C) that span between 39 and 28 Scm−1. Bi2RuMnO7 shows good performance working as a cathode with LSGM electrolyte, yielding output power densities of 360 mW cm−2 at 850 °C with pure H2 as a fuel.