Anode Functional Layer Research Articles

High Performing and Durable Anode-Supported Solid Oxide Fuel Cell by Using Tape Casting, Lamination and Co-Firing Method

This work reports development of large-area (12cm×12cm) planar anode-supported SOFC with 100cm2 active area by a tape casting, lamination and co-sintering method. The cell consists of the nickel-8mol.% yttria-stabilized zirconia as support with 0.7 mm thickness and of the nickel-scandia stabilized zirconia (ScSZ) as an anode functional layer. Processing optimization of binder/plasticizer ratio of tape casting slurry allowed to obtain the green tapes with good mechanical strength and homogenous microstructure. Casting process parameter had also a great influence on the microstructure and mechanical properties of green tapes. The anode-support showed high mechanical strength and sufficient porosity for gas transport. A 6µm thick ScSZ electrolyte and 3µm thick gadolinium-doped ceria (GDC) buffer layer were fabricated using tape casting method and co-firing process. A lanthanum strontium cobalt ferrite-GDC composite cathode was screen-printed on the GDC layer. The single cell showed a peak power density of 509mWcm-2 at 750oC.

Ni-YSZ a New Support for Proton Conducting Fuel Cells

In this research, the possibility of reducing the YSZ content inside the Ni-YSZ support of tubular solid oxide fuel cells (SOFCs) based on proton conducting electrolyte material BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) is studied. The cell consists of a Ni-yttria stabilized zirconia (YSZ) support (with different Ni:YSZ ratios), Ni-BZCYYb anode functional layer (AFL), BZCYYb electrolyte and LSCF-BZCYYb cathode. The results indicate that the addition of only 10 wt% YSZ to the support improves the microstructure by preventing severe Ni grain growth, thereby providing higher density of active sites at the support/AFL interface and more uniform distribution of fuel gas to the active sites. The polarization resistance of the optimized cell with 10 wt% YSZ in the support is lower than the fully Ni supported cell. The promising results of this study reveal that Ni-YSZ can be a suitable support for proton conducting fuel cells.

Development of proton conducting fuel cells using nickel metal support

This research reports the fabrication of a metal supported fuel cell based on the well-known proton conducting electrolyte (PCE) BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) material. The impact of the addition of YSZ on the anode microstructure is also described. This solid oxide fuel cell (SOFC) consists of Ni:yttria stabilized zirconia (YSZ) support (with different weight ratios of Ni:YSZ), Ni-BZCYYb anode functional layer (AFL), BZCYYb electrolyte and LSCF-BZCYYb cathode. The results show that addition of only 10 wt% YSZ to the support improves the microstructure of the cell by preventing severe Ni grain growth inside the support, and providing more accessible triple phase boundaries (TPBs) at the contact surface of the support/AFL and better distribution of the fuel gas to the accessible TPBs. As a result of microstructural improvement, polarization resistance of the cells with 10 wt% YSZ decreases compared with the cell having pure Ni metal. The cell containing YSZ in the support shows 67 h of stable operation under potentiostatic SOFC condition without any degradation. The current metal supported tubular fuel cell shows promising electrochemical and microstructural features which has the possibility to replace the conventional (Ni-PCE) or even Ni-YSZ anode supports.

Multilayer tape casting of large-scale anode-supported thin-film electrolyte solid oxide fuel cells

Tape casting is conventionally used to prepare individual, relatively thick components (i.e., the anode or electrolyte supporting layer) for solid oxide fuel cells (SOFCs). In this research, a multilayer ceramic structure is prepared by sequentially tape casting ceramic slurries of different compositions onto a Mylar carrier followed by co-sintering at 1400 °C. The resulting half-cells contains a 300 μm thick NiO–yttria-stabilized zirconia (YSZ) anode support, a 20 μm NiO–YSZ anode functional layer, and an 8 μm YSZ electrolyte membrane. Complete SOFCs are obtained after applying a Gd0.1Ce0.9O2 (GDC) barrier layer and a Sm0.5Sr0.5CoO3 (SSC) -GDC cathode by using a wet-slurry spray method. The 50 mm × 50 mm SOFCs produce peak power densities of 337, 554, 772, and 923 mW/cm2 at 600, 650, 700, and 750 °C, respectively, on hydrogen fuel. A short stack including four 100 mm × 150 mm cells is assembled and tested. Each stack repeat unit (one cell and one interconnect) generates around 28.5 W of electrical power at a 300 mA/cm2 current density and 700 °C.

Preparation of Freeze-Casted Tubular SOFC with a Modified Anode Functional Layer

Methods that result in randomly orientated porosity are considered conventional for creating micro-porosity within ceramic and cermet structures and coatings that make-up porous electrodes in solid-state, open-system electrochemical devices such as the Solid Oxide Fuel Cell (SOFC). The porosity is necessary to allow sufficient transport of gas species to and away from active sites at the electrode-electrolyte interfaces. Alignment of micro-porosity in porous electrode structures is considered ideal when considering mass transport and tortuosity of gas species diffusing in and out of the active sites. Aligned, micro-porosity can be achieved with the freeze-cast process during which ice-templating is used as the primary agent for pore formation and structural manipulation. In this research, we present a refined method to manufacture and electrochemically evaluate tubular SOFCs (T-SOFCs) whereabout the supporting electrode structure is formed by using the freeze-casting process. All additional layers of the electrochemical cell are achieved via a conventional dip-coating technique. The casting temperature is selected such that ice-templating results in platelet-like structuring of the particles within the ceramic tube, which in this case is designated as the anode of the SOFC, and with alignment of porosity in the radial direction. The anode materials consist of nickel metal and yttrium stabilized zirconium oxide particles homogenously dispersed throughout the bulk anode structure. We show that the total porosity of the tube, under selected experimental conditions, is approximately 50% thus requiring a more conductive anode functional layer connecting the bulk, anode tube to the solid-state electrolyte coating. The anode functional layer is also critical as an intermediate support layer to allow for a dense electrolyte coating to be applied onto such a porous support that has more porosity than conventional anodes which typically have < 30% total bulk porosity. The tubular anode support with the anode functional layer and electrolyte is imaged with scanning electron microscopy to reveal the plate-like microstructure of ceramic particles orientated within the porous network. The solid-state electrolyte is composed of scandium stabilized zirconium oxide while the anode functional layer is composed of nickel metal and scandium stabilized zirconium oxide particles homogenously mixed together within the coating. Complete, T-SOFCs are fabricated and evaluated by additionally coating a ceria-based barrier layer underneath that of a cathode outer layer composed of a standard lanthanum strontium cobalt ferrite perovskite material, which results in a full, electrochemical cell. Polarization curves show a maximum power density of 500mW per cm2 at 800 oC under low fuel utilization conditions using dry hydrogen at a feed pressure of about 250 Pascals above atmospheric pressure and air provided in abundance with respect to the stoichiometric requirement around the outside of the cathode in the testing furnace. Two-wire, electrical impedance spectroscopy with scanning frequencies from 100kHz to 0.05Hz at open circuit potential (OCV), varying load conditions, and with varying perturbation AC signals corresponding to the different load conditions reveal the contributions of overpotentials at both high and low fuel utilization conditions in the temperature range of 700 oC to 800 oC. Figure 1

Design and Fabrication of Solid Electrolyte for the Prevention of Electrode/Electrolyte Delamination

The stability of a solid oxide cell is strongly dependent on the magnitude and profile of internal chemical potential of solid electrolyte. If internal partial pressure is abnormally high, the electrolyte can be delaminated from the electrodes. The formation of high internal pressure is attributed to very low electronic conduction in solid electrolyte. This phenomenon can be significant when the cell is subjected to abnormal operation conditions such as a negative cell voltage. Herein, we suggest a new design of single layer solid electrolyte having local electronic conduction for the prevention of electrode/electrolyte delamination. YSZ and (NiO + YSZ + CeO2) were prepared as electrolyte and anode functional layer, respectively, and these layers were co-sintered at a high temperature, leading to diffusion of cerium ion into YSZ electrolyte. EDS analysis revealed that electronic conduction was locally developed at the anode/electrolyte interface region. The cells were tested under a negative voltage condition using potentiostat. The results indicate that the addition of electronic conduction in the electrolyte can effectively depress internal pressure and prevent anode/electrolyte delamination.

Development of Large-Scale Proton-Conducting Fuel Cells for Next Generation SOFC

Solid oxide fuel cells (SOFCs) are known to exhibit an exceptional energy conversion efficiency over 80 % of the various fuel cell types and have environmentally friendly systems with fuel flexibility. Unfortunately, the SOFC based on yttria-stabilized zirconia (YSZ) electrolytes has a major obstacle to commercialization due to its high cost and low durability at high operating temperature range (800~1000 oC). To overcome this issue, many researchers have made efforts in studying materials with performance comparable to conventional SOFCs at intermediate temperature range (500~700 oC). Among these efforts, to use a proton conductive material with a perovskite structure (ABO3) is regarded as an attractive solution. A lot of previous literatures have already proved the potential of proton-conducting oxide fuel cells (PCFCs) as a next generation of SOFCs. However, most of the results are based on laboratory-scale, so the reliability and feasibility have not been confirmed yet. In the attempt of entering the market with the PCFCs, several issues that must be faced are related to large-scale production. Firstly, when it comes to large-scale cell, the difference in the thermal expansion coefficient (TEC) between the electrode and the electrolyte dominantly affects the overall mechanical property of cells. So, the shrinkage rate after sintering should be elaborately controlled to inhibit several problems such as cracking, lifting and warping. Secondly, the low sinterability of BaCeO3 based proton conductors requires a high sintering temperature, which is more serious problem particularly in large-scale cells. That is, the possibility of Ba evaporation during the heat treatment increase, involving in formation of a secondary phase, which eventually causes performance deterioration. To our knowledge, few literatures are reported on this topic, large-scale PCFCs fabrication. In this work, we attempt to establish large-scale anode-supported PCFCs with BaCe0.6Zr0.2Y0.1Yb0.1 produced by citric-nitrate synthesis method. The electrostatic slurry spray deposition (ESSD) technology was used for each layer fabrication of large-scale cells. An anode functional layer (AFL) was adopted to adjust the TEC and shrinkage rate between the anode and the electrolyte. The quantitative shrinkage rates depending on temperature were analyzed by Dilatometer (Linseis Co.). A scanning electron microscope (SEM, JEOL Co.) was used for microstructural analysis. To examine Ba evaporation and interlayer diffusion, energy dispersive X-Ray spectroscopy (EDX) was used, and the phase development of the synthesized BCZYYb was analyzed by X-ray diffractometer (XRD, Rigaku Co.). The I-V curves and impedance spectra of the single cell were measured in the range of 500 ℃~700 ℃ with humidified hydrogen (~3 % water vapor). Finally, a short-term stability test (100 hours) was performed to confirm the electrochemical durability.

Palladium incorporation at the anode of thin-film solid oxide fuel cells and its effect on direct utilization of butane fuel at 600 °C

Fuel flexibility, which is one of the most important advantages of the solid oxide fuel cell, can be compromised at lower operating temperatures. Thus in this study, normal butane is selected as the fuel and multiscale-architectured thin-film-based solid oxide fuel cells are operated in direct butane utilization mode at T = 600 °C. Palladium (Pd) is chosen as the secondary catalyst to assist the reforming of the butane and is inserted at different positions at the anode. By combining two different Pd insertion methods, sputtering and infiltration, four different thin-film-based solid oxide fuel cells were prepared: (1) the cell without Pd (Ref-cell); (2) the cell with Pd at the anode functional layer, which was fabricated by alternating sputtered Pd layers with pulsed-laser deposited NiO/yttria-stabilized zirconia layers (Pd-S-cell); (3) the cell with Pd at the anode support, which was fabricated by infiltration (Ref-I-cell); and (4) the cell with Pd at both the anode functional layer and anode support (Pd-S-I-cell). As expected, different Pd distributions were observed along the thickness of the anode. The Pd-S-I-cell showed significant enhancement in performance and durability. Approximately three times cell performance enhancement for the best case is observed in comparison with that of the Ref-cell. The Pd distribution, not only at the anode functional layer but also at the anode support, appears to have accelerated the electrochemical and thermochemical reactions. In addition, a lesser degree of carbon deposition was observed at the anode of the Pd-S-I-cell as compared with the case of the others.

Fabrication of an anode functional layer for an electrolyte-supported solid oxide fuel cell using electrohydrodynamic jet printing**Report presented at 9th International Workshop on Advanced Materials Science and Nanotechnology (IWAMSN2018), 7–11 November 2018, Ninh Binh City, Vietnam

Electrohydrodynamic jet (E-jet) printing is an advanced printing technique using an electric field to create the flow of inks from a nozzle via electrohydrodynamics. This technique can deliver very small droplets or flows of inks for high resolution printing. Here, we describe the fabrication of an anode functional layer for an electrolyte-supported solid oxide fuel cells using E-jet printing technique. An ink containing nickel oxide and 10% scandia-stabilized zirconia (10ScSZ) was used to print on an electrolyte plate. Different printing parameters were investigated to vary the structure and morphology of the printed layer. A multiple anode functional layer was fabricated following the optimal printing parameters. The results showed that the thickness of the lines of the printed grid-structured layer could be altered by changing the printing speed. In addition, the grid interval could be easily adjusted. Moreover, multiple overlapped grid layers could be quickly fabricated by printing another layer on a printed dried layer. This anode structure is very beneficial for fuel cell since it possesses a high porosity for quick diffusion of fuel gas and an increased active surface area for enhancing electrochemical reactions. The results showed that the open-circuit voltage (OCV) values of both cells were approximately 1.1 V although the anode functional layer fabricated by using E-jet printing was 7–10 times thinner than that using screen printing.

Advanced impedance model for double-layered solid oxide fuel cell cermet anodes

In state-of-the-art, anode-supported, solid oxide fuel cells (SOFC) the fuel electrode is made of two different porous Ni/stabilized zirconia layers, both with specified phase compositions and microstructural characteristics. It is generally assumed that electro-oxidation of fuel takes place in the thinner anode functional layer (AFL) adjacent to the electrolyte, while gas diffusion takes place in the thicker anode substrate (AS). This assumption is not always applicable and established models fail.This paper introduces a generally valid equivalent circuit model by means of a three-channel transmission line model (3CTLM) that considers electro-oxidation, ionic conduction and gas diffusion. It is parameterized by (i) impedance measurements on model-electrodes, (ii) conductivity measurements, (iii) FIB/SEM-tomography and (iv) gas theory. The complex impedance curve is derived by a newly developed numerical routine that uses calculation steps from network analysis. A model validation is performed by comparing measured and simulated impedance spectra of anode-supported SOFCs varying in AFL thickness from 3 to 22 μm.The 3CTLM is capable of predicting the impedance of any Ni/stabilized zirconia anode design. A model-based optimization is demonstrated, selecting different ionic conducting phases in AFL and AS for combinations of Ni/10Sc1CeSZ, Ni/8YSZ and Ni/3YSZ, across a temperature range of 600–900 °C.

Improvement of output performance of solid oxide fuel cell by optimizing the active anode functional layer

In this work, the effects of an anode functional layer (AFL) with various thicknesses on the physical properties of anode and the electrochemical performance of the anode-supported solid oxide fuel cells (SOFCs) have been systematically studied. Four anode-supported cells with controllable AFL thicknesses have been fabricated by the combined phase-inversion co-tape casting method, screen-printing and dip-coating method. An optimal thickness of the AFL of 7.6 μm is determined by the experimental results including the physical properties and electrochemical performance, and cell performance is significantly enhanced after the introduction of the AFL, which is ascribed to the remarkably increased triple-phase boundaries induced by the AFL. The bilayer anode-supported cells with 7.6 μm thick AFL exhibit a peak power density of 0.906 Wcm−2 and a total resistance of 0.47 Ωcm2 at 700 °C when the anode and the cathode are exposed a humidified H2 (3 vol% H2O) and ambient air, respectively. Additionally, when the anode side is fed with the diluted H2 (3 vol% H2O-97 vol% (10% H2–90% N2)), an excellent peak power density of 0.558 Wcm−2 is still achieved. These results demonstrate that the bilayer anode is a suitable candidate for high-performance SOFC applications, especially at a low hydrogen concentration.

Effect of magnetron sputtered anode functional layer on the anode-supported solid oxide fuel cell performance

Nickel oxide-yttria stabilized zirconia (NiO-YSZ) thin films were reactively sputter-deposited by pulsed direct current magnetron sputtering from the Ni and ZrY targets onto heated commercial NiO-YSZ substrates. The microstructure and composition of the deposited films were investigated with regard to application as thin anode functional layers (AFLs) for solid oxide fuel cells (SOFCs). The pore size, microstructure and phase composition of both as-deposited and annealed at 1200 °C for 2 h AFLs were studied by scanning electron microscopy and X-ray diffractometry and controlled by changing the deposition process parameters. The results show that annealing in air at 1200 °C is required to improve structural homogeneity of the films. NiO-YSZ films have pores and grains of several hundred nanometers in size after reduction in hydrogen. Adhesion of deposited films was evaluated by scratch test. Anode-supported solid oxide fuel cells with the magnetron sputtered anode functional layer, YSZ electrolyte and La0.6Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O2 (LSCF/CGO) cathode were fabricated and tested. Influence of thin anode functional layer on performance of anode-supported SOFCs was studied. It was shown that electrochemical properties of the single fuel cells depend on the NiO volume content in the NiO-YSZ anode functional layer. Microstructural changes of NiO-YSZ layers after nickel reduction-oxidation (redox) cycling were studied. After nine redox cycles at 750 °C in partial oxidation conditions, the cell with the anode NiO-YSZ layer showed stable open circuit voltage values with the power density decrease by 11% only.

Sintered powder-base cathode over vacuum-deposited thin-film electrolyte of low-temperature solid oxide fuel cell: Performance and stability

To expand the processing options for low-temperature-operating solid oxide fuel cells (LT-SOFCs), the hybridization of powder processing and vacuum deposition is attempted. Nanostructured nickel-yttria-stabilized zirconia (Ni-YSZ) anode functional layer (AFL) and YSZ/gadolinia-doped ceria (GDC) bi-layer electrolyte are fabricated over a sintered anode support by pulsed laser deposition (PLD), a physical vapor deposition technology. The most common powder-processed (screen-printed and sintered) La0.6Sr0.4Co0.2Fe0.8O3-δ-Gd0.1Ce0.9O1.95 (LSCF-GDC) composite cathode is applied over vacuum-deposited thin-film components. When LSCF-GDC is sintered at a general sintering temperature of 1050 °C then the continuity of the GDC buffer is lost and excessive interdiffusion between the cathode and the electrolyte has occurred at the interface. On the other hand, if the sintering temperature is lowered to 950 °C, peak power density more than 1.7 W cm−2 at 650 °C is obtained. Moreover, the operation stability of the hybrid SOFC (degradation rate ∼8%/100 h) is superior to that of the SOFC with a vacuum-processed nanostructure cathode (degradation rate ∼21%/100 h) when exposed to 0.7 A cm−2 at 650 °C, which is a significantly harsh degradation test condition for LT-SOFCs.

Electrochemical property of multi-layer anode supported solid oxide fuel cell fabricated through sequential tape-casting and co-firing

In this work, a multi-layer anode supported solid oxide fuel cell (SOFC) is designed and successfully prepared through sequential tape casting and co-firing. The single cell is consisted of NiO-3YSZ (3YSZ: 3 mol.% yttria doped zirconia) anode support, NiO-8YSZ (8YSZ: 8 mol.% yttria stabilized zirconia) anode functional layer, dense 8YSZ electrolyte layer, and porous 3YSZ cathode scaffold layer with infiltrated La0.6Sr0.4Co0.2Fe0.8O3-δ cathode. The clear interfaces and good contacts between each layer, without element inter-diffusion being observed, suggest that this sequential tape casting and co-firing is a feasible and successful route for anode supported single cell fabrication. This cell exhibits remarkable high open circuit voltage of 1.097 V at 800°C under room temperature humidified hydrogen, with highly dense and gastight electrolyte layer. It provides a power density of 360 mW/cm2 under operation voltage of 0.75 V at 800°C and a stable operation of ∼110 h at 750°C under current density of −300 mA/cm2. Furthermore, this cell also presents encouraging electrochemical responses under various anode hydrogen partial pressures and maintains high power output at low fuel concentrations.

NiO-GDC10/GDC10/LSCF-GDC10 Manufactured By Tape Casting and Reactive Magnetron Sputtering Processes of Solid Oxide Fuel Cells

We developed a cost–effective a method to manufacture performance planar solid oxide fuel cells using composite electrode by tape casting and electrolyte by reactive magnetron sputtering. NiO and GDC (10% Gd), used for the anode-supported (as) and the anode functional layer (afl) powders were milled by using zirconia balls in a Turbula-(System Schatz from WAB) times up to 24 hours. Half-cell, 28 mm of diameter, Ni-GDC composite anodes have been fabricated by slurry based tape casting (Elcometer4340 Automatic Film Applicator) method for anode supported solid oxide fuel cell. Depending on the results, work on the support anode (AS) Ni0-GDC will continue in particular to avoid the presence of the residual phase of carbon resulting from the use of an agent poro formers with graphite . The decomposition of organic additives and the shrinkage of green tape is analyzed thermo-gravimetric and differential thermal analysis (TG) of anode. PVD by plasma emission monitoring (PEM) was employed to synthesize GDC (10%Gd doped ceria) thin films on anode-grade ceramic substrate (porous NiO-GDC10). An Alcatel SCM650 sputtering chamber was used for synthesizing the dense GDC layers. A Ce-Gd metallic target (90-10% at) was powered by a pinnacle + pulsed current generator from Advanced Energy under reactive atmosphere.The cathode, which is made of (LSCF-GDC10) was screen printed onto electrolyte film and sintered to form a complete SOFC. The obtained cell after sintering was seen without any deformation or crack. Pycnometry and porosimetry techniques were primarily used to determine pore size and pore volume by equation Washburn and Ideal gas law-method and the decomposition of organic additives and the shrinkage of green tape was analyzed thermo-gravimetric of NiO-GDC10 and LSCF-GDC10. The microstructural morphological surface features of the cell was by 3D profilometry and complete cell were analyzed by Scanning Electron Microscopy (SEM), XRD and was employed to nos-destructively quantify the craking and behavior observed before and after different annealing. The measurements will be carried out on a complete cell with the measuring bench of the company Fiaxell of 5*5 cm2 and on a cell of 28 mm of diameter in order to obtain curves I / V.

High‐Performance Protonic Ceramic Fuel Cells with 1 µm Thick Y:Ba(Ce, Zr)O3 Electrolytes

AbstractThis study demonstrates the effectiveness of using thin‐film electrolytes to enhance protonic ceramic fuel cells (PCFCs). The material tested in this study is yttrium‐doped barium cerate‐zirconate (BCZY), which is a representative electrolyte material of PCFCs. The thickness of the electrolyte membrane is as small as 1 µm and designed to minimize ohmic loss in proton transport pathways. Integration of this thin BCZY electrolyte is attempted on a multilayered anode comprised of two‐step supports with bulk nickel‐yttria stabilized zirconia cermet as a base and thin nickel‐BCZY as an anode functional layer atop the base. The compatibility of this support with the deposited thin electrolyte is able to be confirmed from the results of iterated tests. The power of the fabricated cell is greater than 1.1 W cm−2 at 600 °C, which is a record high for PCFCs and is reproducible. In this paper, the origin of this high power is discussed and improvements that could be made to cell performance are further suggested.

Characterization of Solid Oxide Fuel Cells with LSCF-SDC Composite Cathodes

This paper reports the study of an anode-supported SOFC cell containing an LSCF-SDC composite cathode. The SOFC cell was tested at different temperatures and reactant flow rates. After testing, the cell was sectioned and characterized using SEM/EDS. Such analysis indicated that no structural damage and no significant interdiffusion of elements among the layers occurred. The measured electrochemical performance data at different temperatures indicate an Arrhenius behavior or temperature activated processes. The low-porosity anode functional layer appears to be very sensitive to low hydrogen contents. The electrochemical performance is also affected by changing air flow rates.

Influence of Anode Functional Layers on Electrochemical Performance and Mechanical Strength in Microtubular Solid Oxide Fuel Cells Fabricated by Gel-Casting

Anode-supported microtubular solid oxide fuel cells (mT-SOFCs) using samaria-doped ceria (SDC) as electrolyte were fabricated, varying the composition and number of anode functional layers (AFLs), by combining the aqueous gel-casting and spray-coating techniques. Suitable aqueous slurry formulation of NiO–SDC was prepared using agarose as a gelling agent for gel-casting of tubular supports. Afterward, 40:60 and 50:50 NiO:SDC (wt %) as AFLs and SDC electrolyte were deposited by spray-coating and subsequently co-sintered. Finally, mT-SOFCs with 2.5 mm outer diameter and thicknesses of 380 μm support; 0, 12, and 24 μm AFLs; 15 μm electrolyte; and 30 μm cathode were obtained. The influence of AFLs on the performance and mechanical integrity was investigated for the three cells. For this purpose, electrochemical and mechanical tests at both macroscopic and micro-/nanometric scales (at the AFLs region) were determined by flexural strength and nanoindentation techniques, respectively. The results evidence that t...

Three-dimensional thermal stress analysis of the re-oxidized Ni-YSZ anode functional layer in solid oxide fuel cells

Nickel-yttria-stabilized zirconia (Ni-YSZ) cermet is widely used as an anode material in solid oxide fuel cells (SOFCs); however, Ni re-oxidation causes critical problems due to volume expansion, which causes high thermal stress. We fabricated a Ni-YSZ anode functional layer (AFL), which is an essential component in high-performance SOFCs, and re-oxidized it to investigate the related three-dimensional (3D) microstructural and thermo-mechanical effects. A 3D model of the re-oxidized AFL was generated using focused ion beam-scanning electron microscope (FIB-SEM) tomography. Re-oxidation of the Ni phase caused significant volumetric expansion, which was confirmed via image analysis and calculation of the volume fraction, connectivity, and two-phase boundary density. Finite element analysis (FEA) with simulated heating to 500–900 °C confirmed that the thermal stress in re-oxidized Ni-YSZ is concentrated at the boundaries between YSZ and re-oxidized NiO (nickel oxide). NiO is subjected to more stress than YSZ. Stress exceeding the fracture stress of 8 mol% YSZ appears primarily at 800 °C or higher. The stress is also more severe near the electrolyte-anode boundary than in the Ni-YSZ cermet and the YSZ regions. This may be responsible for the electrolyte membrane delamination and fracture that are observed during high-temperature operation.

Profiled Anode Supported Solid Oxide Fuel Cells for Low Cost Stacks for Stationary Applications

This work presents the results of elaboration of technology dedicated to fabrication of anode supported solid oxide fuel cells (AS-SOFC) with profiled surface of the anode. Profile on anode support was designed as channels which allow to facilitate the fluxes of gaseous components to and from electrochemical reaction zone due to the decreased thickness on Ni-YSZ composites between ribs. Additionally profiling of the anode increases the active area and allows elimination of the profiled or corrugated interconnectors. At state-of-the-art, in order to collect current from the surface of AS-SOFC and to ensure proper distribution of the fuel flow, interconnects are made from special heat-resistant alloys with precise milled or stamped channels. Profiled anode supports will allow to distribute gaseous fuel and replace dual-side profiled interconnects by cheaper ones without introduction of additional treatments or parts. In order to produce anode support with profiled surface without necessity of additional machining process of anode surface, the ceramic injection molding method (CIM) was used. This method significantly shortens the production time of the anode supports for AS-SOFCs, reduces its costs in comparison to commonly used techniques and is generates negligible amount of process waste material. This technique makes it possible to manufacture complex three dimensional ceramic components with tight dimensional tolerances. Cost-intensive post-processing can frequently be avoided, which allows high-scalable mass production of ceramic elements. The mold for injection of anode support was designed to make an anode support of 50x50 mm with 1.4 mm of thickness. The profile consisted of 18 channels was fabricated along of one side of the support. Dimensions of each channel were 0.6 mm of depth and 1.5 mm of width (Fig. 1). The geometry of channels defined using numerical simulations and then adjusted to the technological requirements of CIM. Using this mold the anode supports consisted of NiO/8YSZ 66/34 wt.% with porosity of 25 vol.% were injected (Fig. 1). The screen printing method was used to print 3 µm thick NiO anode contact layer, 7 µm thick NiO/8YSZ 50/50 wt.% anode functional layer, 4 µm thick 8YSZ dense electrolyte, 1.5 µm thick Gd0.1Ce0.9O2 barrier layer and the 30 µm thick La0.6Sr0.4Fe0.8Co0,2O3–δ cathode with porosity 25 vol.%. Sintering conditions were adjusted to avoid the deformation of the anode support. Fig.1. Schematic drawing of the profiled anode support (left) and the anode with fuel channels (right) Fabricated AS-SOFCs were characterized by the microstructural analysis and electrochemical performance was measured. Figure 1