Cathode Current-collecting Layer Research Articles

Highly robust and porous cathode current collecting layer for flat-tubular solid oxide fuel cell stack applications

Solid oxide fuel cells (SOFCs) have gained great attention as a stationary power generation application due to their high efficiency, fuel flexibility and environmental friendliness. The devices and power age could be revolutionized with the commercialization of these technologies. The SOFC-based stationary power generator is one step closer to commercialization however, it is delayed due to the inherent bottleneck of insufficient long-term durability. The cathode current collecting layer (CCCL) is crucial in stack applications to minimize the contact loss between cell and metallic interconnects. Herein, we report an easy-to-fabricate and highly robust CCCL to boost electrochemical performance and long-term durability of flat tubular (FT) short stack. The tailored structure of the CCCL was employed in the fabrication of the FT short-stack. The G/Ag porous structure exhibited increased porosity of 61.2 %, thereby enhancing the mass transport and improving the overall performance and long-term durability. The four-cell FT stack was manufactured without an interconnect and open air-gas channel. Subsequently, the FT short-stack is tested for performance and long-term durability for elapsed 5000 h at a chronopotentiometry test. The porous layer of graphite/Ag on the cathode layer maintained structural integrity without defects and mechanical failure. Consequently, the stack voltage remains stable throughout operation owing to improved structural stability and uniform temperature distribution across four FT cell stack.

Microtubular solid oxide fuel cells with a two-layer LSCF/BSCFM5 cathode

In this study, we present the development of microtubular solid oxide fuel cells (MT-SOFC) with a two-layer cathode: a composite cathode functional layer (CFL) adjacent to the buffer layer (BL) and a cathode current-collecting layer (CCCL). CFL consists of a mixture of BL material Ce0.9Sm0.2O1.95 (SDC) and perovskite Ba0.5Sr0.5Co0.75Fe0.2Mo0.05O3-δ (BSCFM5), which has a high exchange rate with oxygen. The widely used cathode material La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) with high electrical conductivity was used as the CCCL. A significant increase in the peak power density of the MT-SOFC to 1.2 W/cm2 at 850 °C was achieved using the proposed two-layer cathode.

Optimization of Polarization Resistance of (Cu,Mn)3O4 as Cathode Current‐Collecting Layer for Solid Oxide Fuel Cells

The polarization resistance optimization of the cathode plays a crucial role in reducing the energy consumption of the solid oxide fuel cell (SOFC) stack. Herein, a (Cu,Mn)3O4 spinel material is used for the development of the cathode current‐collecting layer (CCCL) because it has superior price and good electrical conductivity than conventional current‐collecting materials. Symmetrical cells are fabricated using screen printing techniques. It is optimized by studying the influence of sintering temperature, thickness, and adding amount of Co3O4 on the microstructure and polarization resistance of the CCCL. The research found that 850 °C is the most convenient sintering temperature and 1–2 wt% of the adding amount of Co3O4 can optimize the polarization resistance. In addition, it is found that for the cathode side, the total thickness of the CCCL and the cathode should be controlled between 70 and 80 μm, the performance of the cathode is stable, and the polarization resistance is also rationally optimized.

On the dependence of interfacial resistance on contact materials between cathode and interconnect in solid oxide fuel cells

The dependence of interfacial contact resistance (ICR) on contact materials between cathode and interconnect is systematically studied under both isothermal oxidation and thermal cycling conditions. Three kinds of cathode current-collecting layer (CCCL) are used, (La,Sr) (Co,Fe)O3 (LSCF), LSCF+10%Ag, and Ag, and tested in a SUS430/CCCL/SUS430 sandwich structure to simulate the actual operation of the solid oxide fuel cells (SOFCs). Experimental results show that the ICR of LSCF+10%Ag exhibits the smallest value, in comparison with the specimens with LSCF and Ag paste, as well as the sample without a CCCL. For LSCF+10%Ag contact, the ICR increases from 0.0069 mΩ cm2 to 3.74 mΩ cm2 under an isothermal condition for 150 h, then increases from 3.74 mΩ cm2 to 10.79 mΩ cm2 after 15 thermal cycles. This work provides information for the understanding of possible mechanisms of performance degradation of SOFCs.

Flexible Cu1.5Mn1.5O4 combined with Co3O4 and Al2O3 conductive ceramic film as a cathode current collecting layer for solid oxide fuel cells

Novel flexible conductive ceramic films consisting of Cu1.5Mn1.5O4, Co3O4 and Al2O3 are developed for the cathode current collecting layer (CCCL) in solid oxide fuel cell (SOFC) stacks. These ceramic films are prepared by a water-based tape-casting method and sintered in situ at the operation temperature of intermediate temperature (IT)-SOFCs. The effects of addition amounts of Co3O4 and Al2O3 on the electrical conductivity of the CCCL and area specific resistance (ASR) of (La0.75Sr0.25)0.95MnO3-δ (LSM) cathode/the CCCL/SUS430 interconnect sandwich are studied. The results indicate that adding 3 wt.% of Co3O4 as sintering aids in Cu1.5Mn1.5O4 precursor powder can promote its sintering and thus reduce its contact resistance with neighboring components. Further combining Al2O3 as the binder with Cu1.5Mn1.5O4-3 wt.% Co3O4, though electrical conductivity of obtained materials decreases with the amount of Al2O3 addition increasing, the minimum ASR of 24.4 mΩ cm2 at 800 °C and a stable ASR of around 27 mΩ cm2 at 750 °C are achieved on LSM cathode/Cu1.5Mn1.5O4-3 wt.% Co3O4-10 wt.% Al2O3 CCCL/SUS430 interconnect sandwich. The developed flexible CCCL shows pronounced low contact resistance and high stability. Moreover, it can be easily cut and sintered in situ in SOFC stack, which is promising for the practical application in SOFC stacks.

Factors of cathode current-collecting layer affecting cell performance inside solid oxide fuel cell stacks

Factors of cathode current-collecting layer (CCCL) affecting cell performance are studied by investigation of solid oxide fuel cell (SOFC) stacks with various (La0.75Sr0.25)0.95MnO3−δ (LSM) as CCCL in-suit. A larger real contact area between cathode and interconnect appears when the LSM is coated on cathode side as CCCL through characterization of a 2-cell stack. The result reveals that the real contact area depends on the surface roughness match (SRM) between CCCL and its neighboring components (active cathode and interconnect). A 6-cell stack using CCCLs with various levels of surface roughness is assembled and characterized further. The results show a higher electrical output performance of the stack repeating unit can be obtained when the surface roughness of the CCCL matches that of its neighboring components better, i.e. the surface roughness match (SRM) is the factor of cathode current collector affecting cell performance inside stack. Accordingly, the cell performance inside SOFC stack can be regulated by designing the SRM to its neighboring components.

Effect of conductivity and adhesive properties of cathode current-collecting layer on cell performance inside stack for planar solid oxide fuel cells

Effects of conductivity and adhesive properties of cathode current-collecting layer (CCCL) on cathode contact resistance and cell performance inside a solid oxide fuel cell (SOFC) stack during operation are investigated by adding Al2O3 to the CCCL of (La0.75Sr0.25)0.95MnO3+δ (LSM). The conductivity of LSM–15wt% Al2O3 composite CCCL decreases from 141.6Scm−1 to 23.7Scm−1 at 800°C, whereas its adhesion to SUS 430 interconnect and LSM–YSZ active cathode increases by 2.5 and 1.8 times, respectively. The area specific resistance (ASR) of SUS 430/CCCL/LSM–YSZ sandwich at 800°C is tested. The result shows that ASR of SUS 430/ LSM–15wt% Al2O3 /LSM–YSZ sandwich is approximately 2.5 times smaller than that of the SUS 430/LSM /LSM–YSZ sandwich. The maximum output power density (MOPD) of the unit cell with LSM–15wt% Al2O3 CCCL is slightly higher than that of the cell with pure LSM CCCL at 800°C. The degradation rate of the unit cell with LSM–15wt% Al2O3 CCCL is nearly 1/7 of the unit cell with pure LSM being discharged at a constant DC of 0.32Acm−2 for about 100h. Consequently, the addition of adhesive to CCCL is much more conducive to improve the long-term stability of the stack operation.

Quantitative contribution of resistance sources of components to stack performance for planar solid oxide fuel cells

This study detects the resistance that influences the stack performance of SOFCs with composition of Ni-YSZ/YSZ/LSC-YSZ and investigates the variation patterns of the resistances of the stack repeating unit (SRU) during operation and their quantitative contributions to its performance at 700 °C, 750 °C and 800 °C. The results indicate that when the cell cathode contacts the interconnect well, the cell resistance accounts for 70.1–79.7% of that of the SRU, and the contact resistance (CR) between the cathode current-collecting layer (CCCL) and the interconnect accounts for 20.0–28.9%. The CR between the anode current-collecting layer (ACCL) and the interconnect together with the resistance of the interconnect can be neglected during instantaneous I–V testing. When the stack is discharged at constant current for 600 h, cell resistance increases by 28.3%, accounting for 93.3% of the SRU degradation, the anodic CR increases by 36.4%, accounting for 6.7% of the SRU degradation, and the resistances of the cathode contact and its neighbor interconnect remain unchanged. Therefore, the increase of the cell resistance is the main reason causing the SRU degradation, and the anodic contact is also an influencing factor that cannot be neglected during stable operation.

Effect and mechanism of Cr deposition in cathode current collecting layer on cell performance inside stack for planar solid oxide fuel cells

Quantitative effect and mechanism of Cr on cell performance inside stack are investigated by incorporating Cr in the cathode current-collecting layer (CCCL). The results show that the maximum output power density (MOPD) of the unit cell inside a stack decreases as the Cr content increases beyond 253.81 μg cm−2. The MOPD is independent of Cr when its content is less than 253.81 μg cm−2 at the original operation stage. The degradation of the repeating unit inside the stack increases with increasing Cr content. When the Cr content is higher than 182.22 μg cm−2, cell degradation increases. However, cell degradation is independent of Cr content when its content is less than 182.22 μg cm−2. The addition of Cr to the CCCL increases the ohmic resistance of the CCCL and the contact between the cathode and the electrode during the initial stage. The effect of Cr on cell degradation increases with time, but Cr content has no influence on the contact resistance between the interconnect and the cathode. Cell degradation is mainly dependent on ohmic resistance, and is independent of polarization resistance. Therefore, the addition of Cr to the CCCL increases the cell ohmic resistance, but does not affect cell polarization resistance.

Investigation of Impactors on Cell Degradation Inside Planar SOFC Stacks

AbstractThe impactors on cell degradation inside planar SOFC stacks were investigated using both coated and uncoated Fe–16Cr alloys as the interconnects under stable operating conditions at 750 °C and thermal cycling conditions from 750 to 200 °C. It was found that cell degradation inside the stack is primarily dependent on the interfacial contact between the cathode current‐collecting layer and the interconnect. Additionally, cell degradation is found to be independent of the high‐temperature oxidation and Cr vaporization of the interconnects during stack operation, as the stacks are well sealed. The coating on the interconnect can further improve the contact between the cell cathode and the interconnect when the latter is properly embedded into the current‐collecting layer.

Aerosol Jet Printing and Microstructure of SOFC Electrolyte and Cathode Layers

We report the cathode layer optimization efforts undertaken to improve the cell performance of a previously reported (10) aerosol jet printed SOFC with strontium doped lanthanum manganate (LSM) based cathode. The cathode current collection layer, LSM with different thicknesses, solids loading in printing ink, and sintering temperature was examined. These parameters were observed to have a significant impact on the cell performance, changing the maximum power density of cells from 200 - 460 mW/cm2 at 850 ºC, depending on the processing conditions. Low voltage scanning electron microscopy was used to clearly distinguish the different phases of the composite LSM/YSZ layer. This method was used as a diagnostic tool to qualitatively assess the feasibility of "on the fly mixing" of the individually aerosolized inks. Cells with printed gadolinia doped ceria (GDC)-lanthanum strontium cobalt ferrite (LSCF) cathodes showed a performance, about twice that of cells with LSM cathodes.

Effect of Ag-(La 0.8Sr 0.2) 0.95MnO 3 current-collecting layer on the stability of anode-supported solid oxide fuel cell

The anode-supported solid state fuel cells were fabricated by tape-casting and co-sintering techniques. The effects of Ag-(La 0.8Sr 0.2) 0.95MnO 3 (LSM95) current-collecting layer at the cathode side on the electrochemical stability of anode-supported solid oxide fuel cells were investigated. The assembled cell was electrochemically characterized from 800 to 700 °C with humidified H 2 as fuel and O 2 as oxidant. The open circuit voltages decreased with decreasing temperature which were opposite from the results calculated from the Nernst equation for each temperature, and the values were 1.14, 1.09 and 1.03 V at 800, 750 and 700 °C, respectively. EDX analysis revealed that Ag diffused from the cathode current-collecting layer to the surface of electrolyte which was caused by Ag electromigration under current. The phenomenon of Ag electromigration led to unstable cell performance during long-time operation.

Ink‐Jet Printing: A Versatile Method for Multilayer Solid Oxide Fuel Cells Fabrication

The potential of ink‐jet printing for fabrication of components for solid oxide fuel cells has been explored. An anode interlayer, consisting of a composite of NiO and yttria‐stabilized zirconia (YSZ), and an electrolyte layer, YSZ (8 mol%), were ink‐jet printed on a tape cast anode support, 55 wt% NiO–45 wt% YSZ (8 mol%). Scanning electron microscopy of the printed layers sintered at 1400°C revealed a dense electrolyte layer measuring 10–12 μm in thickness. Single cells using these printed layers and strontium‐doped lanthanum manganate (LSM, La0.8Sr0.2MnO3)‐based pasted cathodes were assessed by DC polarization and AC complex impedance methods. The cells exhibited a stable open circuit voltage of 1.1 V around 800°C, in a hydrogen atmosphere. A maximum power density of 500 m·(W·cm)−2 was achieved at 850°C for a typical cell with the electrolyte and anode interlayer cosintered at 1400°C. A composite cathode interlayer, LSM–YSZ, and a cathode current collection layer, LSM, were also ink‐jet printed and incorporated in single cells. However, cells with all components ink‐jet printed showed decreased performance. This pointed to critical issues in the composite cathode microstructure, which is controlled by the composite ink design/formulation and printing parameters that need to be addressed.

A Microscale Modeling Tool for the Design and Optimization of Solid Oxide Fuel Cells

A two dimensional numerical model of a solid oxide fuel cell (SOFC) with electrode functional layers is presented. The model incorporates the partial differential equations for mass transport, electric conduction and electrochemical reactions in the electrode functional layers, the anode support layer, the cathode current collection layer and at the electrode/electrolyte interfaces. A dusty gas model is used in modeling the gas transport in porous electrodes. The model is capable of providing results in good agreement with the experimental I-V relationship. Numerical examples are presented to illustrate the applications of this numerical model as a tool for the design and optimization of SOFCs. For a stack assembly of a pitch width of 2 mm and an interconnect-electrode contact resistance of 0.025 Ωcm2, a typical SOFC stack cell should consist of a rib width of 0.9 mm, a cathode current collection layer thickness of 200–300 μm, a cathode functional layer thickness of 20–40 μm, and an anode functional layer thickness of 10–20 μm in order to achieve optimal performance.

Optimization of Segmented-in-series Tubular SOFCs with an (La, Sr)CoO3 System Cathode and the Generation Characteristics under Pressurization

We studied the application of LaCoO3 system cathode to improve the performance of segmented-in-series tubular type solid oxide fuel cells (SOFCs) operating at high temperature (1173 K). (La1−xSrx)CoO3 (LSC, x=0.2 or more) was chosen to take advantage of two of its properties: high electric conductivity and favorable behavior of element diffusion to a cathode interlayer (CIL) of (Sm0.2Ce0.8)O2 (SDC20). The cell stack performances were compared using LSC and (La0.5Sr0.25Ca0.25)MnO3 (LSCM) to cathode current collection layer (CCCL). The modification of cell stack structure composed of effective generation part and interconnector part was also examined. The area specific resistance (ASR) of the overall cell stack resistance with LSC modifying a stack structure decreased 18% than that of the stack using LSCM with conventional structure at atmospheric pressure. In a pressurized test of the cell stack fabricated with LSC, an increase of pressure resulted in a decrease of the ASR. As a result of comparing the pressurized performances of LSCM CCCL/(LSCM-10YSZ) CIL, LSCM/SDC20 and LSC/SDC20, the effect of ASR decrease by pressurization fell as the cell stack performances improve. We also found, however, that the cell stack fabricated with LSC will require improvements in long-term durability and thermal cycle characteristics.

Effect of cathode current-collecting layer on unit-cell performance of anode-supported solid oxide fuel cells

According to the characterization of the microstructure and properties of solid oxide fuel cells (SOFC) electrodes, it is essential to verify various processing variables to control microstructural parameters, such as particle size, composition and spatial distribution of the constituent phases of the electrode in order to reduce the ohmic and diffusional polarization losses of the unit-cell performance. From this viewpoint, a current-collecting layer with controlled microstructure very effectively enhances the unit-cell performance by reducing the ohmic and polarization resistance of the cathode. The maximum power density of a 5 cm × 5 cm unit-cell with the controlled current-collecting layer is ∼1.5 W cm −2 at 750 °C, while a unit-cell without the layer is much lower, viz., 0.9 W cm −2.