Lanthanum Strontium Manganite Cathode Research Articles

Revised Zero-Dimensional Model for a Solid Oxide Fuel Cell with Mo-Doped Ceria Anode Using Syngas as Fuel

A zero-dimensional model was implemented to simulate the performance of a solid oxide fuel cell (SOFC) with Mo-doped ceria (CMO) anode using humidified (3%v/v water) hydrogen or syngas (50%v/v H2 – 50%v/v CO) as fuel. The model was validated preliminarily through experimental data generated at 800ºC using a SOFC with coated electrodes supported in the electrolyte (a 20 mm diameter yttria-stabilized zirconia, YSZ, disc) with a 14 mm diameter CMO|CMO-YSZ anode and a 14 mm diameter LSM-YSZ|LSM (lanthanum strontium manganite) cathode. Polarization (cell voltage vs current density, ΔEcell vs j) and power density (power density vs current density, Pelec vs j) curves were generated via linear sweep voltammetry connecting the SOFC to a Gamry Reference 3000 potentiostat/galvanostat/ZRA using platinum mesh and wires.The open circuit voltage (OCV) of the SOFC operating with humidified hydrogen was modelled directly using Nernst equations for the electrochemical hydrogen oxidation and oxygen reduction reactions. For the case of the SOFC operating with humidified syngas, the electrochemical hydrogen and carbon monoxide oxidation reactions occur simultaneously at the anode. Hence, the Nernst equation was corrected by each anodic reaction selectivity determined solving mass balances coupled to an electrochemical kinetics model.Figure 1.a shows the fitted polarization and power density curves. Maximum SOFC power densities of ca. 1295 W m-2 (at 0.53 V and 2434 A m-2) and ca. 1084 W m-2 (at 0.52 V and 2106 A m-2) are predicted for the cell operating with humidified hydrogen and humidified syngas as fuel, respectively. These values are 2 and 5% lower than the experimental values. The OCVs calculated are ca. 1.10 V and 1.01 V, respectively, which are 5 and 8% higher/lower than the experimental values. The differences observed are attributed to the non-ideality of the gases due to their interaction with the electrode surfaces, and the possible infiltration of air into the anodic chamber [1,2].The SOFC ohmic losses calculated represent ca. 72% of the total voltage losses when operating at the maximum power density, which are attributed to the low electrical conductivities of the CMO|CMO-YSZ anode (CMO electrical conductivity is ca. 0.501 S m-1 at 800ºC [3]) and the thick electrolyte (ca. 2.203 S m-1 at 800ºC [4]). Improvements are being introduced to the anode material by including nickel, which will contribute to increase the hydrogen oxidation kinetics while CMO protects the electrode from carbon deposition when syngas is used as fuel. Presently, activation losses represent ca. 28% of the total voltage losses at the maximum power density. It has been reported that for SOFCs using syngas as fuel, the anode active sites are more occupied by carbon monoxide molecules due to their slower oxidation kinetics in comparison with hydrogen. Nevertheless, carbon monoxide is also susceptible to undergo a surface reforming process via the water-gas shift reaction. Such phenomenon becomes more relevant at high carbon monoxide concentrations, which was the case in this study (50% v/v CO), thus favoring the electricity generation through hydrogen oxidation at the anode surface [2].For the SOFC using humidified syngas as fuel, the model assumes that the desorption equilibrium pressure of hydrogen (pH2 *) on the surface of molybdenum in the CMO|CMO-YSZ anode is equal to that reported for humidified hydrogen on the surface of nickel in Ni-YSZ anodes (0.09 atm) [5]. Figure 1.b shows the results obtained for the sensitivity analysis of the model as a function of pH2 *, which indicates that unless its value is increased by ca. 220% over 0.09 atm the exchange current density for carbon monoxide oxidation (j0,CO) does not go below its lower confidence limit. It is unlikely that this parameter reaches such level of discrepancy because it implies that hydrogen adsorption at the anode surface is strongly diminished, thus electrochemical oxidation kinetics decrease considerably which is not consistent with the experimental observations.Future work includes the analysis of the kinetic parameters dependence on the temperature and the fuels partial pressures.

A solid oxide fuel cell with molten tin anode for electricity generation and methane reforming

A methane-fuelled solid oxide fuel cell (SOFC) with molten tin anode (Sn(l)-SOFC) is designed, fabricated, demonstrated and characterized. This SOFC design incorporates molten tin contained in an alumina crucible as anode for the solution of oxygen atoms transported to an anode | Yttria stabilized Zirconia (YSZ) electrolyte interface and provides bubble | molten tin interfaces for the reaction of methane with oxygen atoms during cell operation. A peak power density of ca. 100 W m−2 at a current density of 222 A m−2 and potential difference of 0.45 V is obtained for this methane-fuelled Sn(l)-SOFC at 850 °C. The ohmic and non-ohmic impedance are ca. 16.72 and 3.36 Ω cm2, respectively. Ohmic potential losses control the reactor performance, with about ca. 59% of those arising from the inherent difficulty in achieving a low resistance contact at the silver wire (silver wool) current collector | Lanthanum strontium manganite cathode interface. Improved performance is achievable by eliminating contact resistance, utilising a molten metal/alloy with greater activity for methane oxidation and operating the cell at higher temperatures. The reaction of methane at bubble | molten tin interface involves its coupling in addition to oxidation, to produce steam, carbon dioxide, hydrogen, ethane and ethylene.

Improving fuel cell performance via optimal parameters identification through fuzzy logic based-modeling and optimization

Improving the performance of solid oxide fuel cell via maximizing its available peak power density is a key requirement of research in the field of renewable energy. This could be achieved through identifying the optimal controlling parameters such as, the deposition instrument power (P), the temperature (T), and the electrolyte thickness (Thick). Nickel–Gadolinium Doped Ceria cermet anode films are deposited on one side of the Zirconia electrolyte by radio frequency sputtering. The sputtering plasma power is varied at 50, 100, 150, and 200 W. Lanthanum Strontium Manganite cathodes were screen-printed on the other side of the electrolyte supports to complete the configuration. Cells were electrochemically tested at various intermediate solid oxide fuel cell temperatures of 600, 700 and 800 °C using different electrolyte thicknesses. The cell’s current density, I (A/cm2) and voltage (V) and hence the power density (W/cm2) are recorded in each case. Based on the obtained experimental results, a fuzzy model is built using different control parameters. Then, the particle swarm optimization technique is used for obtaining the best parameters of the cell that maximizes its power density. The results show that by utilizing the optimized conditions, the power density can be increased to 0.39 (W/cm2), which is almost two times higher than the maximum power density obtained experimentally.

Controlling Porosity of Anode Support in Tubular Solid Oxide Fuel Cells by Freeze Casting

Abstract Precise porosity control is highly desirable for improving the electrochemical performance of solid oxide fuel cells (SOFCs). Freeze casting is an established method for enabling high bulk porosity in structures and controlling pore orientation. In this study, freeze casting was used to fabricate tubular, anode-supported SOFCs with aligned and varying amounts of porosity by controlling the solids/water ratio in different casting slurries. SOFCs were prepared with a Ni/yttria and scandia stabilized zirconia (ScYSZ) anode support (AS), an anode functional layer (AFL), a ScYSZ electrolyte, a lanthanum strontium manganite (LSM)/ScYSZ cathode interlayer (CIL), and an LSM cathode. The permeability of the anode support was found to increase from 1.4 × 10−2 to 1.8 × 10−2 m2 as porosity was increased from 57 to 64 vol%, while the total cell resistance decreased by 35% from 0.93 to 0.60 Ohm cm2. When evaluated with 30 vol% H2 as the fuel at 800 °C, the decrease of concentration polarization enabled an increase in electrochemical performance by 42% from 0.35 to 0.50 W/cm2 as the porosity in the anode support was increased. Mechanical strength characterization using a three-point method showed there is a practical upper limit of the amount of porosity that can be designed into the anode support. This work paves a way for controlling porosity by freeze casting and understanding the correlation between porosity and concentration polarization losses in SOFCs.

Composition-gradient protective coatings for solid oxide fuel cell interconnectors

Protective Ni-based coatings for stainless steel current collectors of the planar solid oxide fuel cells (SOFCs) were developed and tested during 21,000 h in contact with lanthanum-strontium manganite cathode material. The compositional and microstructural alterations due to interdiffusion between Ni coating, La0.8Sr0.2MnO3 electrode and commercial Crofer 22 APU steel after long-term testing under the SOFC cathodic conditions, were studied. The results of micro-Raman spectroscopy and electron microscopy analyses showed a dominant role of Mn and Fe diffusion into the protective coating, leading to the formation of NiFe2O4 and MnFe2O4. Although Mn deficiency in the manganite cathode may decrease electrical conductivity, its impact on the overall contact resistance is insignificant. The Ni-based coatings were found to decrease area-specific interfacial resistivity down to 3–4 mOhm × cm2 for, at least, 21,000 h (>2.5 years) at 1123 K, atmospheric oxygen pressure and current density of 0.5 A/cm2.

The influence of nanoparticle aggregation on formation of ZrO2 electrolyte thin films by electrophoretic deposition

The paper presents the results of the studies of electrically stabilized nonaqueous suspensions of ZrO2 stabilized by Y2O3 (YSZ) nanoparticles with an average diameter of 11nm for the formation of green films of electrolyte for solid oxide fuel cells. Nanoparticles were de-aggregated to different degrees, which were provided by the ultrasonic treatment and the centrifugation, and monitored by the dynamic light scattering. YSZ green thin films were obtained by the electrophoretic deposition (EPD) on dense lanthanum strontium manganite cathodes using suspensions with the average diameter of aggregates: 107; 66; 53nm. To investigate the possibilities of EPD we used the model drying of the same suspensions cast upon the same substrates. It was shown that the structure and the morphology of the green films obtained by EPD was different compared to the films prepared by the model drying of the suspension. The drying of the stable suspension resulted in the formation of loose aggregates on the surface. The efficient packing of electrically stabilized particles was prevented by the forces of electrostatic repulsion between them. In the case of EPD the electrocoagulation of particles near the cathode takes place with the formation of dense aggregates. As a result, uncharged spherical aggregates with an average size of about 100–200nm settle on the surface of the cathode and pack into a uniform dense coating suitable for the subsequent sintering of a gas-tight coating for the solid YSZ electrolyte.

Exchange current model for (La0.8Sr0.2)0.95MnO3 (LSM) porous cathode for solid oxide fuel cells

In this paper, we propose an empirical formula for i0,TPB, the exchange current density per unit triple-phase boundary (TPB) length, for porous lanthanum strontium manganite (LSM) cathodes of solid oxide fuel cells (SOFCs); the evaluation of i0,TPB is of crucial importance in numerical simulations of electrodes based on reconstructed microstructures obtained by a dual beam focused ion beam scanning electron microscopy (FIB-SEM) and tomography techniques. To derive a widely applicable empirical formula for i0,TPB, electrochemical measurements of porous LSM cathodes are conducted under various oxygen partial pressures (0.05–0.25 atm) and temperatures (800–950 °C). By comparing the derived formula with that derived from a thin and dense patterned LSM electrode used in previous studies, it is found that at an air temperature of 800 °C, i0,TPB derived from a porous LSM cathode is approximately 40% smaller than that for the patterned electrode. This can be attributed to the fact that the electrochemical reaction in thin and dense electrodes can occur not only at the TPBs but also at the LSM surface owing to the non-negligible ionic conductivity of LSM. The derived formula is also applied to a three-dimensional numerical simulation to confirm its validity.

Improved chromium-poisoning on lanthanum strontium manganite cathode in presence of a newly developed iron-chromium based interconnect alloy for solid oxide fuel cells

A newly developed interconnect alloy for solid oxide fuel cells, containing Fe, Cr, Mn and Mo as well as other minor elements and designated as FeCM, is investigated on its poisoning effect on (La0.8Sr0.2)0.95MnO3−δ (LSM) cathode by electrochemical impedance spectroscopy and microstructure observation. Compared with commercial SUS430 stainless steel, which is usually used as a essential interconnect in the SOFCs stacks, the FeCM alloy as the interconnect reduces the ohmic of the cell (RΩ) and polarization resistance of the cathode (RP) and increases the electrochemical performance of the cathode. At 850 °C the RΩ remains almost unchanged at a level slightly above 2.0 Ω cm2 and the RP decreases from 5.76 to 1.68 Ω cm2 within 20 h, while the cathode potential at 200 mA min−1 is virtually stabilized at below 1.0 V and the overpotential is decreased from 0.43 to 0.16 V. Based on the evidence of a narrower oxide deposition zone on the electrolyte surface near the cathode and a deposition-free cathode/electrolyte interface, this improvement is attributed to the reduced degree of volatilization of oxide scale formed on the surface of the FeCM alloy.

Evaluation of Exchange Current Density for LSM Porous Cathode Based on Measurement of Three-Phase Boundary Length

Here we propose an empirical formula for the exchange current density per unit TPB (three-phase boundary) length for porous LSM (lanthanum strontium manganite) cathodes for solid oxide fuel cells, which is often required for numerical modeling of cathode performance based on reconstructed microstructures obtained with tomography techniques. Electrochemical measurement of LSM cathodes was conducted under various oxygen partial pressure (0.05-0.25 atm) and temperature (800-950 °C) conditions. The derived values were compared with those from a thin and dense patterned LSM electrode in literature, and were found to be small at 800 °C. One of the possible reasons is that the charge transfer can be occurred at not only TPB but also two-phase (LSM-Pore) boundary in the case of thin patterned electrode.

Performance regeneration in lanthanum strontium manganite cathode during exposure to H<sub>2</sub>O and CO<sub>2</sub> containing ambient air atmospheres

The regenerability and stability of lanthanum strontium manganite (LSM)/yttria doped zirconia (YSZ)/LSM symmetrical cells have been examined after the cells were exposed to real-world air environment containing H2O and CO2. An alternate exposure experiment in 20% H2O-air and dry air has been conducted to test the reversibility of the cell degradation in H2O/air. Long-term experiment in 3% H2O-0.5% CO2-air, dry air, 0.5% CO2-air, and 10% CO2-air has shown the stability and regenerability of the cell performance. Additional experiments show that periodic water content fluctuation causes the cell performance fluctuation. Electrochemical performance measurements and post-test microstructure analysis indicate that the segregation of SrO on the LSM surface and formation of La2Zr2O7 at the LSM/YSZ interface degraded the electrochemical performance by increasing the polarization resistance. The cell performance degradation can be partially recovered by exposure to dry air. Thermogravimetric analysis (TGA) has been conducted for the LSM as well as its constituent oxides to elucidate degradation mechanisms. Mechanisms related to the performance degradation and regenerability have been proposed.

Oxide film formation and diffusion processes in near-surface layers of current collectors in solid oxide fuel cells

A method is developed for modifying the surface of current collectors in solid-oxide fuel cells (SOFC) prepared from ferrite stainless steel (Crofer22APU). Diffusion of the protective coating material into the Crofer22APU bulk and reverse diffusion of steel components into the coating are studied. The cross-sectional microstructure and composition are studied by the electron-microscopic technique. The elemental composition of the junction between the current collector and the lanthanum-strontium manganite cathode is studied depending on the time of service-life tests in the SOFC working mode (50–6000 h). The formation of the Cr2O3 oxide islet structure on the current collector surface at the steel/coating interface is observed. It is shown that the mutual diffusion of coating components (Ni) and Crofer22APU steel together with the redox reaction at the interface prevent the chromium diffusion to the surface and protect the steel current collector from oxidation.

Phase Inversion and Electrophoretic Deposition Processes for Fabrication of Micro-Tubular Hollow Fiber SOFCs

A novel combination of a phase inversion process followed by electrophoretic deposition was used to fabricate anode supported micro-tubular hollow fiber solid oxide fuel cells (SOFCs). The phase inversion process was used to produce 240 μm thick 60 wt% NiO - 40 wt% yttria-stabilized zirconia (YSZ) hollow fiber anode precursors with asymmetric porosity. Subsequently, electrophoretic deposition (EPD) was used to apply 40 μm thick, particulate YSZ electrolyte layers onto the un-sintered NiO-YSZ hollow fibers from a YSZ dispersion in ethanol at an applied electric field of ca. 22 kV m−1. The YSZ-coated NiO-YSZ fibers were sintered in a hydrogen atmosphere at 1500°C to produce gastight electrolytes. Two dispersions of YSZ and lanthanum strontium manganite (LSM) particles were then painted consecutively on top of the electrolyte layers, as ‘graded’ LSM-YSZ | LSM cathode precursors that were sintered at 1200°C. When fed with H2 fuel and air, a single such SOFC delivered peak power densities of 0.20, 0.18 and 0.14 W cm−2 during operation at 800, 750 and 700°C, respectively. A lumped parameter model, incorporating calculations of the contact, ohmic, activation and concentration polarization losses, is presented and the means are proposed by which certain potential losses may be obviated.

Three‐Dimensional Reconstruction and Microstructure Modeling of Porosity‐Graded Cathode Using Focused Ion Beam and Homogenization Techniques

AbstractIn this study, microstructure of a porosity‐graded lanthanum strontium manganite (LSM) cathode of solid oxide fuel cells (SOFCs) has been characterized using focused ion beam (FIB) and scanning electron microscopy (SEM) combined with image processing. Two‐point correlation functions of the two‐dimensional (2D) images taken along the direction of porosity gradient are used to reconstruct a three‐dimensional (3D) microstructure. The effective elastic modulus of the two‐phase porosity‐graded cathode is predicted using strong contrast (SC) and composite inclusion (CI) homogenization techniques. The effectiveness of the two methods in predicting the effective elastic properties of the porosity‐graded LSM cathode is investigated in comparison with the results obtained from the finite element model (FEM).

Structural and impedance analysis of copper doped LSM cathode for IT-SOFCs

Copper-doped lanthanum strontium manganite (LSM) system, La0.8Sr0.2Mn1−xCuxO3−δ (0⩽x⩽0.3), was synthesized using the EDTA-combined citrate process and their characteristics were investigated for solid oxide fuel cell (SOFC) cathode applications. In all compositions, a single perovskite phase was obtained after calcination at 750°C for 10h. The maximum electrical conductivity at elevated temperatures was obtained at a composition of x=0.2 (190Scm−1 at 750°C), whereas the sample with x=0.3 showed the minimum value (100Scm−1 at 750°C). The increase in electrical conductivity with increasing Cu contents was attributed to a charge compensating transition of the Mn3+–Mn4+ and the reason for the decreased value, at x=0.3, is mainly due to the presence of a second phase. The cathode area specific resistance of the sample with x=0.2 was 4.3Ωcm2 at 750°C, which is lower than that of LSM (x=0). The enhanced performance with the addition of Cu can be explained by the additional Mn4+ promoting the formation of surface oxygen vacancies when Mn4+ is converted to Mn3+ at high temperatures. Copper ion doping at the B-site of LSM affects the formation of oxygen vacancies, which can enhance the oxygen reduction reaction.

Component interactions after long-term operation of an SOFC stack with LSM cathode

The reliable long-term operation of stacks with a low degradation rate is a prerequisite for the commercialization of solid oxide fuel cell (SOFC) technology. A detailed post-test analysis of stacks is of major importance in understanding degradation mechanisms. Here the results are reported of a post-test analysis of an SOFC stack with anode supported cells with Ni/YSZ anode, 8YSZ electrolyte, and a lanthanum strontium manganite (LSM) cathode operated under steady-state conditions for 19,000 h. In particular, the microstructural and chemical analyses of the relevant metallic and ceramic components are reported. The interconnects were coated with a (Mn,Co,Fe) 3O 4 spinel by atmospheric plasma spraying, which prevented Cr evaporating into the cathode compartment. The diffusion of Mn from the (La,Sr)MnO 3 cathode into the 8YSZ electrolyte led to local enrichment at grain boundaries, which might have been responsible for the degradation via electronic pathways leading to partial short-circuiting across the electrolyte. However, the ultimate failure of the stack was the result of a weakening and fracture of the 8YSZ electrolyte along grain boundaries due to the local Mn enrichment.

Sensitivity of Stresses and Failure Mechanisms in SOFCs to the Mechanical Properties and Geometry of the Constitutive Layers

AbstractA model based on the Euler–Bernoulli theory is used to assess the sensitivity of residual stresses in solid oxide fuel cells to the mechanical properties and geometry of the constituents. It considers different cell configurations, characterised by the presence or not of a compensating layer, and a cathode based on either lanthanum strontium manganite (LSM) or lanthanum strontium cobaltite ferrite (LSCF). The implementation of creep in the model provides insights into the parameters that affect the zero‐stress temperature and behaviour during ageing. The amount of irreversible deformation generated in the cell layers after the sintering step depends on the mechanical properties of the layers, type of cell and to some extent, cooling rate. X‐ray diffraction measurements from literature are used to verify the prediction. Depending on the mechanical properties, the stress state in the LSM cathode changes from tensile to compressive with respect to temperature. During combined ageing and thermal cycling, tensile stress might arise in the compatibility layer of LSCF‐based cells, due to the relief of the initial compressive stress at operating temperature. The Weibull analysis provides the assessment of mechanical failure. A simplified approach is used for buckling‐driven delamination, but the propagation of cracks is predicted for unlikely large pre‐existing defects.

Solid Oxide Fuel Cell Fueled by Diesel Reformate and Anaerobic Digester Gas

A solid oxide fuel cell with a nickel-yttria stabilized zirconia cermet anode and a porous lanthanum strontium manganite cathode was used to generate electrical power directly from anaerobic digester gas and commercial diesel steam reformate. A diesel reformer was combined with the solid oxide fuel cell system in a single operating unit to convert diesel to electricity. To model anaerobic digester gas (ADG), a fuel gas mixture was prepared based on analytical data on real ADG from a local water cleaning facility. Electrochemical performance characterization involved power generation across a variety of external loads to characterize open circuit potential, maximum power densities and limiting current densities. The effects of anode poisoning from of sulfur compounds and their removal from the ADG fuel were studied.

Electrochemical properties of nanostructured lanthanum strontium manganite cathode fabricated by electrostatic spray deposition

Electrostatic spray deposition was applied to prepare nanoporous lanthanum strontium manganite (LSM) films with high specific surface area (37.34 m 2/g) for the cathode application in solid oxide fuel cell (SOFC). The electrochemical characteristics were investigated at a temperature range from 546 to 777 °C and oxygen partial pressure from 0.01 to 1.0 atm. The diffusion of atomic oxygen and oxygen ion transfer from three-phase boundary to the YSZ electrolyte were found to be the rate-determining steps for oxygen reduction reaction on LSM cathode. The polarization resistance of the LSM prepared using electrostatic spray deposition decreased from 15 to 1.2 Ωcm 2 with increasing temperature from 546 to 777 °C and the activation energy was 0.81 eV. It was demonstrated that the ESD method offers a promising approach for the preparation of electrochemically active nanoporous layers, particularly applicable for solid oxide fuel cells.

Thin Film (La0.7Sr0.3)0.95MnO3-δFabricated by Pulsed Laser Deposition and Its Application as a Solid Oxide Fuel Cell Cathode for Low-Temperature Operation

The feasibility of using the thin film technology in utilizing lanthanum strontium manganite (LSM) for a solid oxide fuel cell (SOFC) cathode in a low-temperature regime is investigated in this study. Thin film LSM cathodes were fabricated using pulsed laser deposition (PLD) on anode-supported SOFCs with yttria-stabilized zirconia (YSZ) electrolytes. Although cells with a 1 ㎛ thick LSM cathode showed poor low-temperature cell performance compared to that of a cell with a bulk-processed cathode due to the lack of a triple-phase boundary length, the cell with 200 ㎚-thick gadolinia-doped ceria (GDC) inserted between the LSM and YSZ showed enhanced performance and more stable operation characteristics in a comparison of a cell without a GDC layer. We postulate that the GDC layer likely improved the cathode adhesion, therefore contributing to the improvement of the cell performance instead of serving as an interfacial reaction buffer.

Geometrical Optimization of Double Layer LSM/LSM-YSZ Cathodes by Electrochemical Impedance Spectroscopy

The present-day high-temperature solid oxide fuel cells (SOFCs), based on yttria-stabilized zirconia (YSZ) electrolyte, a lanthanum-strontium manganite (LSM) cathode and a nickel-YSZ cermet anode, operate at 800–1000°C. Cathode materials are restricted to doped lanthanum manganites due to their stability in oxidizing atmosphere, sufficient electrical conductivity, and thermal expansion match to the YSZ electrolyte. Reduction in the operating temperature of SOFCs is desirable to lower the costs and to overcome the technological disadvantages associated with elevated temperatures. However, as the operating temperature is reduced, the decrease in the LSM conductivity and increase in interfacial polarization resistances between the LSM cathode and YSZ electrolyte become critical. Therefore, different approaches have been proposed to improve interfacial quality and electrochemical performance of the LSM/YSZ cathode. The length of the triple-phase boundary (TPB) correlates well with the interfacial resistances to electrochemical oxidation of hydrogen at the anode and reduction in oxygen at the cathode. The extension of the TPB or the number of active reaction sites becomes, therefore, a determining factor in improving electrode performance. This can be achieved by developing electrode materials of higher ambipolar conductivity and by optimizing the microstructure of the electrodes. In order to improve SOFC performance, both composition and structure of the LSM/YSZ interface and of the cathode should be optimized. Recently, functional grade materials (FGMs) were introduced for SOFC technology. However, all studies reported in the literature so far, were focused on cathodes with only compositional gradient. On the other hand, intuitionally the best structure for a functional SOFC should be characterized by both compositional and porosity gradients. Fine grains (and high surface area) close to the electrode/electrolyte surface and large grains (and thus large pore size) at the air/oxygen side are expected to be of advantage. In the present study, “symmetrical” cathode-electrolyte-cathode SOFC single cells were fabricated. The cells consisted of the functional grade LSM cathode with YSZ/LSM cathode functional layer and LSM contact layer. The effects of various geometrical and microstructural parameters of cathode/functional layers on the overall cell performance were systematically investigated. The parameters investigated were the (1) cathode functional layer thickness and grain size and (2) the LSM contact layer thickness. Cathode performances were tested by means of electrochemical impedance spectroscopy (EIS) over a temperature range of 650–950°C, using air as oxidant. The dependence of cell performance on various parameters was rationalized by a comprehensive microscale model. A cathode polarization corresponding to 0.14–0.4 Ω cm2 at 750°C was achieved in this manner.