Cathode Polarization Resistance Research Articles

Er0.4Bi1.6O3−δ – La0.8Sr0.2MnO3−δ nano-composite as a low-temperature firing cathode of solid oxide fuel cell

Er0.4Bi1.6O3−δ (ESB) composited with La0.8Sr0.2MnO3−δ (LSM) (2:3 or 3:2 wt:wt) with a bonding aid to decrease firing temperature TF are screen-printed on symmetric single cells composed of a Gd0.2Ce0.8O2−δ (GDC) interlayer/yttria-stabilized zirconia (YSZ) electrolyte/GDC interlayer, and their impedance spectra are compared. Addition of 5 wt % CuO to ESB-LSM (3:2 wt:wt) decreases the cathode TF to 650 °C without increasing cathodic polarization resistance (Rp ∼0.19 Ω cm2 at 650 °C). This ESB-LSM composite can be used as a cathode that can be fired at low temperature.

Experimental and thermodynamic evaluation of La1−xSrxMnO3±δ and La1−xSrxCo1−yFeyO3−δ cathodes in Cr-containing humidified air

Chemical and structural stability of strontium doped lanthanum manganite (LSM) and lanthanum cobalt ferrite (LSCF) cathodes in Cr-containing humidified air has been studied by a combination of experimental and thermodynamic approaches. During 100 h tests performed in flowing air (3% H2O) at 1023 K, the electrochemical performance of LSM/yttria doped zirconia (YSZ)/Pt half-cells exhibited a relatively faster degradation in current (I–t) at 0.5 V applied bias than the LSCF/gadolinium-doped ceria (GDC)/Pt half-cells. Cr species from the gas phase deposited predominantly at LSM/YSZ interface while LSCF showed mainly surface deposition throughout the electrode. Raman spectra indicate SrCrO4 formation on the post tested LSCF cathode but not on the post tested LSM cathode. The polarization resistance of the LSM cathode also increased significantly compared to that of the LSCF cathode. A linear programming approach coupled with first-principles thermodynamics suggests that the stoichiometric LSM remains stable and unreacted for the whole range of experimental PCrO3 and temperature conditions whereas the formation of SrCrO4 on LSC cathode is energetically favored at 1023 K supporting the experimental findings.

Novel BaBi0.05Co0.8Ta0.15O3−δ cathode material for intermediate temperature solid oxide fuel cells

Cathode material BaBi0.05Co0.8Ta0.15O3−δ (BBCT) was synthesized by a solid-state reaction for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The X-ray techniques had been used for structural characterizations. BBCT forms a pure cubic perovskite structure and exhibits chemical compatibility with the La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) electrolyte. The thermal expansion coefficient (TEC) of the BBCT is 20×10−6K−1. The electrical conductivity are 7.4–10.7Scm−1 in the temperature range of 600–800°C in ambient air. The polarization resistance (RP) of BBCT cathode on LSGM electrolyte is 0.023, 0.036, 0.065Ωcm2 at 800, 750, 700°C, respectively. Maximum power density is 664mWcm−2 at 800°C. The encouraging results promise BBCT as an alternative cathode material for IT-SOFCs.

Characterization of laser-processed thin ceramic membranes for electrolyte-supported solid oxide fuel cells

By laser machining we have prepared thin and self-supported yttria stabilized zirconia (YSZ) electrolytes that can be used in electrolyte-supported solid oxide fuel cells for reducing the operation temperature. The membranes, which are supported by thicker areas of the same material, have an active area of ∼20 μm in thickness and up to 8 mm in diameter. Buckling limits the maximum size of the thin areas to below 1 mm, the overall effective active area being formed by multiple thin areas bounded by ribs. Electron Backscattering Diffraction experiments determined that there are not significant strains inside the membranes and that the heat-affected zone is confined to a shallow layer of ∼1–2 μm. The bending strength of the membranes decreases by ∼26% as a result of the surface microcracking produced by the laser machining. The membranes have a roughness of ∼2.5 μm and are coated by a layer of nanoparticles produced by the laser ablation. This coating and small roughness is not detrimental for the cathodic polarization of the cells. Conversely, the cathode polarization resistance decreases ∼5% in the 650–850 °C temperature range.

A CO2-tolerant La2NiO4+δ-coated PrBa0.5Sr0.5Co1.5Fe0.5O5+δ cathode for intermediate temperature solid oxide fuel cells

La2NiO4+δ (LN)-coated PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) composite cathode, designated as PBSCF-LN, for the intermediate temperature solid oxide fuel cells (IT-SOFCs) is prepared by solution infiltration, and investigated comparatively with single phase PBSCF cathode in the half and full cells using Ag and/or Pt paste as the current collector. Compared with Pt, Ag current collector results in a decrease of cathode polarization resistance (RP) by an order of magnitude, which suggests that Ag is electrocatalytically active and not suitable for the use of studying the cathode performance of IT-SOFCs. The RP value of PBSCF-LN cathode is significantly lower than that of PBSCF cathode, no matter whether Pt or Ag current collector is used for the measurement. High power densities ranging from 0.24 to 0.94 W cm−2 at temperatures between 600 and 750 °C are achieved using a full cell with PBSCF-LN cathode. Upon exposure to a CO2-rich atmosphere, carbonate particles are formed on the surface of PBSCF cathode, causing irreversible degradation of electrochemical performance. In contrast, the surface of PBSCF-LN cathode remains clean, and its performance degradation due to CO2 adsorption is recoverable.

Enhancement of the interfacial polarization resistance of La0.6Sr0.4Co0.2Fe0.8O3-δ cathode by microwave-assisted combustion method

Thermogravimetry, phase formation, microstructural evolution, specific surface area, and electrical properties of La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathode were studied as functions of its preparation technique. The pure perovskite LSCF cathode powder was synthesized through glycine–nitrate process (GNP) using microwave heating technique. Compared with conventional heating technique, microwave heating allows the rapid combustion to occur simultaneously between the nitrates and glycine in a controllable manner. The resulting powder is a single-phase nanocrystallite with a mean particle size of 113nm and a high specific surface area of 12.2m2/g, after calcination at 800°C. Impedance analysis indicates that microwave heating has significantly reduced the polarization resistance of LSCF cathode. The area specific resistance (ASR) value of 0.059 and 0.097Ωcm2 at 800°C and 750°C, respectively, were observed. These values were twofold lower than the corresponding ASR of the cathode (0.133 and 0.259Ωcm2 at 800°C and 750°C, respectively) prepared through conventional heating. Results suggest that the microwave heating GNP strongly contributes to the enhancement of the LSCF cathode performance for intermediate temperature solid oxide fuel cells.

A new composite cathode for intermediate temperature solid oxide fuel cells with zirconia-based electrolytes

Abstract Improving the electrocatalytic activity of electrode materials is vitally important to achieve practically meaningful performance for intermediate temperature solid oxide fuel cells (IT-SOFCs). The present work develops a composite cathode consisting of an electronic conductor Sr-doped LaMnO 3 (LSM) and an ionic conductor Y- and Ce- co-doped Bi 2 O 3 (BYC7). BYC7 is an excellent oxide-ion conductor, exhibiting a high and stable ionic conductivity of 0.008 S cm −1 at 500 °C. The polarization resistance of LSM-BYC7 cathode in a symmetrical cell with doped ZrO 2 as electrolyte varies from 5.76 at 500 °C to 0.25 Ω cm 2 at 650 °C. The surface diffusion and charge transfer at the triple phase boundaries are the rate determining steps based on the dependence of polarization resistance on partial pressure of oxygen. The maximum power density of a ZrO 2 -based anode-supported cell with LSM-BYC7 composite cathode is 56.4, 154.6, 327.9, and 451.0 mW cm −2 at 500, 550, 600, and 650 °C respectively. AC impedance analysis reveals that the performance of IT-SOFC prepared in this study is actually limited by the anode, not by LSM-BYC7 cathode.

Oxygen transportation, electrical conductivity and electrochemical properties of layered perovskite SmBa0.5Sr0.5Co2O5+δ

Oxygen transportation properties of SmBa0.5Sr0.5Co2O5+δ (SBSC55) layered perovskite has been investigated as a potential cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). This research includes the following items: (1) structural characteristics, thermogravimetric behavior, oxygen permeation, chemical bulk diffusion coefficient (Dchem), and (2) the electrochemical performance of long-term testing carried out to evaluate its electrochemical stability. The Dchem values for SBSC55 cathode are 2.6 × 10−6, 9.1 × 10−6 and 1.8 × 10−5 cm2 s−1 at 500 °C, 600 °C, and 700 °C, respectively. The oxygen permeation flux for SBSC55 membrane with 1.0 mm thickness increased from 0.143 mL min−1 cm−2 at 500 °C to 0.406 mL min−1 cm−2 at 800 °C under synthetic air at a flow rate of 50 mL min−1, helium at a rate of 25 mL min−1. The activation energies of oxygen permeation for the high temperature region (700–800 °C) and low temperature region (500–650 °C) are 23.67 and 6.96 kJ mol−1, respectively. It suggested that oxygen diffusion for high temperature range is surface exchange process, low temperature range is bulk diffusion process. The long-term test of cathodic polarization resistance for SBSC55∣SDC∣SSBSC55 half-cell at 600 °C during 96 h has been carried out with an increase rate of 0.30% h−1. Based on the impedance spectra with various oxygen partial pressure results, the rate-limiting process of ORR is determined that the oxygen ion transfer from triple-phase boundary (TPB) and/or two-phase boundary (2PB) sites of cathode is major with the minority of charger transfer reaction.

High performance yttria-stabilized zirconia based intermediate temperature solid oxide fuel cells with double nano layer composite cathode

A composite double layer cathode of La0.6Sr0.4Co0.8Fe0.2O3−δ/La0.8Sr0.2FeO3−δ (LSCF/LSF) was successfully fabricated by infiltration method to accelerate the sluggish oxygen reduction reaction (ORR) processes. In this composite cathode, both LSF and LSCF layers are uniformly distributed on Yttria-stabilized Zirconia (YSZ) scaffold by optimizing the infiltrating solution components. LSF serves as a protective layer between LSCF and YSZ. The introduction of the LSCF exterior layer has greatly improved cell performance compared with the cell with sole LSF cathode. At 600 °C, the maximum power density of the cell with LSCF/LSF/YSZ composite cathode reaches up to 0.559 W cm−2. The evolution of the cathode polarization resistance verifies that the ORR activity has been greatly enhanced. Therefore, the results indicate that the high cell performance at intermediate temperatures can be obtained by adopting the LSCF cathode into YSZ-based SOFCs using protective layer and that the infiltration method is a practical way for constructing electrode.

Relationship Between Designed Three-Dimensional YSZ Electrolyte Surface Area and Performance of Solution-Precursor Plasma-Sprayed La0.8Sr0.2MnO3−δ Cathodes

Active three-phase boundaries (TPBs) significantly influence cathode performance in solid oxide fuel cells, but obtaining long TPBs and understanding the mechanism underlying the improved cathode performance when the electrolyte is prepared with a smooth surface by a high-temperature sintering process remain essential challenges. In this work, we used flame spraying to deposit single-layer semimolten particles on a smooth electrolyte to build a three-dimensional surface with enlarged active surface area and thus increased TPBs. Meanwhile, La0.8Sr0.2MnO3−δ (LSM) cathodes with fine microstructure were deposited by solution-precursor plasma spraying (SPPS) on the designed electrolyte to establish a three-dimensional cathode–electrolyte interface. The deposition behavior of the semimolten particles on the smooth electrolyte and LSM cathodes on the three-dimensional electrolyte surface was studied. The effects of the area enlargement factor (αarea) on the polarization resistance of the SPPS LSM cathodes were investigated, using three-dimensional electrolytes with αarea from 1.29 to 2.48. The results indicated that convex particles with different molten states bonded well with the electrolytes. SPPS LSM cathodes also showed good interfacial bonding with convex particles. Finally, the cathode polarization (Rp) decreased linearly with increase of αarea. At 800 °C, Rp decreased from 0.98 to 0.32 Ω cm2 when αarea was increased from 1.29 to 2.48.

Magnetic field effect on the electrochemical performance of La0.7Sr0.3MnO3-δ cathodes

La 0.7 Sr 0.3 MnO 3 − δ (LSM) magnetic properties are exploited through the application of a magnetic field, resulting in a significant decrease of the cathode polarization resistance, a crucial component of high temperature solid oxide fuel cells. The magnetic field is applied during the drying process after the deposition of LSM cathodes by screen-printing on a Gd0.1Ce0.9O1.95 (GDC) electrolyte. This specific process aims to decrease the cathode polarization resistance of solid oxide fuel cells. X-ray diffraction patterns show a structural modification triggered by the magnetic field. LSM cathode performance is investigated over a temperature range of 700–800 °C by impedance spectroscopy. The measured electrode area specific resistance (ASR) of a LSM/GDC/LSM symmetric half-cell without and with magnetic field was 0.30 Ω cm2 and 0.20 Ω cm2, respectively, at 800 °C. The ASR value was therefore decreased by 33% with the magnetic field effect. This behaviour may be attributed to LSM grain reorientation, microstructure change, and tortuosity modification of LSM cathodes.

Decreasing the Polarization Resistance of BaCo0.7Fe0.2Nb0.1O3–δ Cathodes by Infiltration of Ce0.8Y0.2O2–δ

AbstractCe0.8Y0.2O2–δ (YDC) was infiltrated into a BaCo0.7Fe0.2Nb0.1O3–δ (BCFN) cathode of intermediate temperature sold oxide full cells (IT‐SOFCs) in order to decrease its cathodic polarization resistance. BCFN and YDC infiltrated BCFN electrodes were fabricated on dense Ce0.8Gd0.2O2–δ (GDC) thin pellets to form symmetrical cells. The electrochemical impedance spectra of the symmetrical cells were investigated in this present study. Firstly, the thickness of BCFN electrodes was optimized, and controlled at 30 µm for further study. The effects of infiltrated YDC amount and firing temperature on electrode polarization resistance were studied. The symmetrical cells infiltrated with 30 μL YDC solution and fired at 900 °C exhibited the lowest electrode polarization resistance in all samples. It was suggested that infiltration of YDC resulted in more active sites and prolonged TPBs in electrodes, improving the surface oxygen exchange, and finally improved the electrode performance.

Degradation Analysis of SOFC Stack Performance-Durability Test and Verification of Improved SOFCs-

Central Research Institute of Electric power Industry (CRIEPI) has operated six types of SOFC stacks, which are developed by MITSUBISHI HITACHI POWER SYSTEMS (MHPS), KYOCERA, TOTO, NGK SPARK PLUG, NGK INSULATORS, and MURATA, to reveal their durability and find dominant degradation factor for each SOFC stack under NEDO’s project. The target of this NEDO durability project is set at 0.11%/1,000hr. In order to evaluate a performance degradation of the SOFC quantitatively and in order to quantify a performance change with time, the performance factor analysis method is required. We have been developed the electrode polarization models which is able to express SOFC performance factors such as Nernst loss (ηne), anode polarization (ηa), cathode polarization (ηc), and internal resistance IR drop (ηiR) with high prediction accuracy for six types of SOFCs. This gives us enable to make detail comparison among different type of SOFCs with the same performance analysis method inside the NEDO project. The MHPS’s stack which was operated until 16,000 hours, showed better stability and no further degradation factor has been identified. On the other hand, peculiar degradation behaviors arising from some impurities in air have been observed in our test for the stacks of Kyocera’s, TOTO’s, NTK’s, NGK’s, and Murata’s. For example, performance test exibited a rapid voltage drop within initial operation period for flattened tubular segment-in-series stack. The factor of this rapid voltage drop was increment of cathode overvoltage from a performance factor analysis result. One of possible reason for the negative effect to cathode overvoltage is sulfur contamination in the supply air from air compressor or thermal insulating foam on furnace. In this study, we report our recent activities on the durability and the dominant performance factors, and the peculiar degradation behaviors.

Secondary Phases at Cathode/Electrolyte Interfaces

Understanding the nature of a cathode/electrolyte interface in solid oxide fuel cells (SOFC) is still a challenge, especially if this interface is composed of a mixed conducting cathode, i.e., La1-xSrxCo1-yFeyO3- δ (LSCF), and a bilayer electrolyte, i.e., Gd-doped Ceria (GDC) interlayer and Y2O3 stabilized ZrO2 (YSZ) electrolyte. The interface resistance can vary over more than two orders of magnitude [1], resulting from variable volume and local distribution of the poorly ionic conducting secondary phase SrZrO3(SZO) [2] and GDC-YSZ interdiffusion (ID) [3]. This contribution will introduce a COMSOL Multiphysicsmodel, which simulates the performance characteristics of such heterogeneous cathode/electrolyte interfaces. The model is based on 3D-reconstruction data of an interface region, which was characterized (i) electrically by in-situ electrochemical impedance spectroscopy and (ii) by ex-situ elemental analysis using TEM/EDXS. Our model calculations quantify the contributions of both secondary phases, SZO and ID to the cathodic polarization resistance, but also a contribution of ID to the ohmic resistance, corresponding well to the performance measurements. Our results further reveal that interface morphology, i.e. volume and local distribution of secondary phases, plays a significant role. When GDC is sintered at high temperatures (see Fig.1 at 1300°C) to a continuous and dense ID layer (green color), SZO formation is still significant (turquoise color), but a comparatively small area of “free” pathways for oxygen ions from LSCF→GDC→ID→YSZ can reduce the polarization resistance up to two orders of magnitude. On the contrary; when GDC is sintered at lower temperatures, a much thicker and continuous SZO layer blocks the diffusion of oxygen ions, corresponding to the highest polarization resistance. From our investigation we conclude that because secondary phases are inherently present and their local contribution overshadows every high-performing material property, it is of particular interest to deepen the understanding of functional cathode/electrolyte interfaces by using high-resolution analysis techniques.

Kinetically driven switching and memory phenomena at the interface between a proton-conductive electrolyte and a titanium electrode.

Numerous studies have examined the switching properties of semi- or ion-conductors and isolators; however, most of these have focused on the ohmic resistance characteristics. Here, we report a new type of polarity-dependent switching phenomenon obtained for electrical devices with the configuration: metal working electrode│Si0.97Al0.03H0.03P2O7-polytetrafluoroethylene composite electrolyte│Pt/C counter electrode. The counter electrode is reversibly active for the water vapor oxidation and evolution reactions. The composite electrolyte exhibits high withstanding voltage capability in the bias voltage range of ±7 V. When titanium was employed as the working electrode, the anodic polarization resistance was approximately two orders of magnitude greater than the cathodic polarization resistance. The ohmic resistance of the device was almost unchanged, regardless of the bias voltage polarity. Moreover, kinetically induced high-resistance/low-resistance states could be cyclically switched through positive/negative bias voltage pulses, and these states were also confirmed to be memorized at open circuit.

Decreasing the polarization resistance of LaSrCoO4 cathode by Fe substitution for Ba(Zr0.1Ce0.7Y0.2)O3 based protonic ceramic fuel cells

LaSrCo1−xFexO4−δ layered perovskites with K2NiF4 structure were synthesized successfully via the Pechini method and evaluated as cathode material for Ba(Zr0.1Ce0.7Y0.2)O3 (BCZY) electrolyte supported protonic ceramic fuel cells (PCFCs). X-ray diffraction results show that LaSrCo1−xFexO4−δ (0.0 ≤ x ≤ 0.5) were all single phase with K2NiF4 structure. Thermal expansion coefficient of LaSrCo0.5Fe0.5O4−δ is close to that of BCZY electrolyte. The conductivity of LaSrCo0.5Fe0.5O4−δ in air is 142 S cm−1 at 750 °C. At 750 °C, the Rp of LaSrCo0.5Fe0.5O4−δ is measured and the value is about 0.12 Ω cm2. The main rate-determining step in LaSrCo0.5Fe0.5O4−δ cathode is the dissociation of adsorbed oxygen molecules into atoms on the surface. Further, cathodic overpotential of 90 mV is obtained for LaSrCo0.5Fe0.5O4−δ cathode at current density of 0.2 A cm−2 at 750 °C. The substitution of Co by Fe causes an enhancement of the better electrochemical properties implying that LaSrCo0.5Fe0.5O4−δ could be applied as possible cathode for PCFCs.

Effects of Pr-deficiency on thermal expansion and electrochemical properties in Pr1−xBaCo2O5+δ cathodes for IT-SOFCs

Pr-deficient Pr1−xBaCo2O5+δ (P1−xBCO) oxides are evaluated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). Effects of Pr-deficiency on electrical conductivity, thermal expansion and electrochemical properties are investigated. Both the conductivity and thermal expansion coefficient (TEC) decrease with increasing Pr-deficiency. All of the conductivity, thermal expansion and TGA measurements demonstrate the existence of high temperature order-disorder transition. The oxygen reduction mechanism for P1−xBCO cathodes are characterized by electrochemical impedance spectroscopy. Over the temperature range of 600−800°C, the cathode polarization resistance is mainly contributed from electronic charge transfer over the cathode surface. Proper Pr-deficiency reduces cathode polarization resistance (Rp), and the lowest Rp (0.081Ω cm2 at 700°C) is obtained for the P0.92BCO cathode. In addition, the effects of order-disorder transition on the properties of P1−xBCO cathodes have also been discussed. Maximum power densities of a single-cell with P0.92BCO cathode on 300-μm thick Sm0.2Ce0.8O1.9 (SDC) electrolyte achieve 446–987mWcm−2 at 650–800°C. These results suggest that, among various P1−xBCO oxides, P0.92BCO is the most promising candidate cathode material for IT-SOFCs.

Electrochemical performance of Co-containing mixed oxides as oxygen electrode materials for intermediate-temperature solid oxide electrolysis cells

Composite materials Nd0.8Sr1.2CoO4 − δ – Nd0.5Sr0.5CoO3 − δ were prepared and evaluated as oxygen electrode for intermediate temperature reversible solid oxide cells (IT-RSOCs). Nd0.8Sr1.2CoO4 − δ (NSC0812) material with A2BO4-type structure was prepared by citrate–nitrate combustion method, and Nd1 − xSrxCoO3 − δ (x = 0.3, 0.4, 0.5, 0.6, 0.7) materials with perovskite structure were prepared via the glycine nitrate process (GNP). The crystal structure, thermal expansion, electrical conductivity and electrochemical properties were investigated. The lattice volume of Nd1 − xSrxCoO3 − δ increases with increasing Sr content, x. XRD analysis show that no reaction occurs between oxygen materials and Gd0.2Ce0.8O1.9 (GDC). The thermal expansion coefficient increases with increasing x. AC impedance spectroscopy on symmetric cells was used to assess electrochemical performance of the oxygen electrode materials. Nd0.5Sr0.5CoO3 − δ (NSC0505) has the lowest total cathodic polarization resistance for 0.099 Ω cm2 at 750 °C. The composite materials NSC0505 and NSC0812 with the ratio of 7:3 reveals a better performance than either material individually at 700 °C, which is due to introduce of more oxygen vacancies and oxygen interstitials with NSC0812. For an electrolysis voltage of 1.3 V, current densities in a single cell fabricated with Nd0.5Sr0.5CoO3 − δ – Nd0.8Sr1.2CoO4 − δ are 420 mA cm−2 at 800 °C.

Short review on cobalt-free cathodes for solid oxide fuel cells

Cobalt-containing cathodes are known for their ability to operate under high-temperature applications in solid oxide fuel cells (SOFCs). Reducing the operation temperature into intermediate temperature-to-low temperature (IT-LT) zones may lead to a mismatch in the thermal expansion coefficient between the cathodes and the developed IT-LTSOFC electrolyte materials. Hence, cathode materials are adjusted to resolve this issue. Studies on IT-LTSOFC propose cobalt-free cathodes as an alternative way to produce high electrochemical performance cells for operation within the IT-LT range. Novel cobalt-free cathode powders are developed using perovskite structured materials, such as strontium ferrite oxide, as the main components together with dopants. This paper reviews various studies on cobalt-free cathode development, including the most important parameter in determining cathode performance, namely, the polarization resistance of SOFC cathodes.

Effect of thickness, component and porosity on the polarization resistance of BaCo0.7Fe0.2Nb0.1O3 − δ–Ce0.9Gd0.1O1.95 composite cathode

BaCo0.7Fe0.2Nb0.1O3−δ (BCFN)–Ce0.9Gd0.1O1.95 (GDC) composite cathode is synthesized on GDC electrolyte wafer by using a spin coating method. The effects of preparing conditions such as the spin coated times, the amount and size of pore former on the morphological features (thickness and porosity) have been systematically investigated by scanning electron microscopy and X-ray diffraction. It is shown that the thickness, component and porosity play important roles in determining the polarization resistance of the composite cathode. The polarization resistance of BCFN-GDC composite cathode is 1.85, 0.62, 0.25, 0.14 and 0.05Ωcm2 at 600, 650, 700, 750, and 800°C under the optimal preparation parameters, respectively.