Sequential Tape Casting Research Articles

Bilayer Dense-Porous Li7 La3 Zr2 O12 Membranes for High-Performance Li-Garnet Solid-State Batteries.

Li dendrites form in Li7 La3 Zr2 O12 (LLZO) solid electrolytes due to intrinsic volume changes of Li and the appearance of voids at the Li metal/LLZO interface. Bilayer dense-porous LLZO membranes make for a compelling solution of this pertinent challenge in the field of Li-garnet solid-state batteries (SSB). Lithium is thus stored in the pores of the LLZO, thereby avoiding i) dynamic changes of the anode volume and ii) the formation of voids during Li stripping due to increased surface area of the Li/LLZO interface. The dense layer then additionally reduces the probability of short circuits during cell charging. In this work, a method for producing such bilayer membranes utilizing sequential tape-casting of porous and dense layers is reported. The minimum attainable thicknesses are 8-10µm for dense and 32-35µm for porous layers, enabling gravimetric and volumetric energy densities of Li-garnet SSBs of 279Wh kg-1 and 1003Wh L-1 , respectively. Bilayer LLZO membranes in symmetrical cell configuration exhibit high critical current density up to 6mA cm-2 and cycling stability of over 160 cycles at a current density of 0.5mA cm-2 at an areal capacity limitation of 0.25 mAh cm-2 .

Planar Anode Supported SOFC Fabricated By Sequential Aqueous Tape Casting, Constrained Cosintering and Screen-Printing

Hydrogen technologies and especially fuel cells, are promising alternatives to achieve a carbon-free energy and an ecofriendly transition [1]. The SOFC technology (Solid Oxide Fuel Cell) is an energy conversion system composed of a stack of a porous cathode, a dense electrolyte and a porous anode working at a temperature in the [600°C – 1000°C] range to obtain ionic conductivity above 10-2 S/cm.Nowadays, tape-casting is typically used for mass and low-cost manufacturing of supporting half-cell (8YSZ electrolyte and Ni-YSZ anode) and the cathode layer is commonly deposited by screen-printing [2]. In line with the cost reduction problematic, this presentation will describe the development and optimization of a green sequential tape casting process to obtain the anodic half-cell and screen-printing for the cathode. To target green process, aqueous based slurries are used and only non-toxic organic components are selected. The amount of organic components, ceramic powder and water was optimized to obtain slurries with a shear-thinning behavior while managing the powder dispersion stability. The parameters of the drying heat treatment have been optimized based on Thermal Gravimetric Analysis leading to obtain a multilayer flexible green tape without any bubbles or cracks further annealed to eliminate the organics and co-sinter the stack under a porous YSZ load. The flat anodic half-cell with a thin and dense layer of 8YSZ on a thick and porous layer of NiO-YSZ is completed by screen-printing of La2NiO4+ δ (cathode) based ink followed by a consolidation thermal treatment. The characterization using X-ray diffraction, scanning electron microscopy and operando electrochemical tests of the cell allow validating the efficiency of the sequential tape-casting to fabricate via environmentally friendly process and low cost SOFC.[1] Rissman, J. et al. (2020) ‘Technologies and policies to decarbonize global industry: Review and assessment of mitigation drivers through 2070’, Applied Energy, 266, p. 114848. doi:10.1016/j.apenergy.2020.114848.[2] Udomsilp, D. et al. (2021) ‘Performance Benchmark of Planar Solid Oxide Cells Based on Material Development and Design.’, Energy Technology, 9. doi:10.1002/ente.202001062.

Anode supported planar 5 × 5 cm2 SrZr0.5Ce0.4Y0.1O2.95 based solid oxide protonic fuel cells via sequential tape-casting

Solid oxide protonic fuel cells are one of the most efficient means of directly converting stored chemical energy to usable electrical energy. Acceptor-doped Ba(Zr, Ce)O3 perovskite-type oxides are the preferred electrolyte choice as they provide higher conductivity due to lower activation energy. While substantial progress has been made on small-sized protonic laboratory-scale cells, a considerable challenge has been upscaling robust planar-type devices. This paper employs a cost-effective inverse tape casting route and screen printing to fabricate flat planar anode-supported protonic fuel cells consisting of NiO-SrZr0.5Ce0.4Y0.1O3-δ substrate, SrZr0.5Ce0.4Y0.1O3-δ electrolyte, and BaCo0.4Fe0.4Zr0.1Y 0.1O3-δ as the cathode. The processing parameters were analyzed and adjusted to obtain defect-free single cells of dimension up to 100 mm × 100 mm × 0.5 mm with diminished warping. In addition, the smooth tri-layered green tapes yielded suitably dense and gas-tight electrolyte layers after co-sintering at 1300 °C/5 h. Finally, the electrochemical performance of the 50 × 50 mm2 SrZr0.5Ce0.4Y0.1O2.95 based cells was evaluated, and their impedance spectra were deconvoluted to identify all performance-related polarization processes via the distribution of relaxation time.

Development of Anode-Supported Solid Oxide Fuel Cell by Sequential Tape-Casting and Co-Sintering

Simple and cost-effective technologies to produce solid oxide fuel cells layers require control of thickness, homogeneity, and reproducibility. The manufacturing of a SOFC involves significant ceramic processing challenges to obtain layers with controlled microstructure. Currently, possibly the most common technique for large-scale production of SOFCs is the tape casting. In our study, a co-tape casting process was used to avoid delamination and ensure good adhesion between layers. The process consists of casting a thick anode tape of Ni/YSZ (60/40vol%) on top of a thin electrolyte tape of yttria-stabilized zirconia (YSZ). The slurries of both components were prepared using commercial ceramic powders, organic additives, and solvent. The starting materials were processed in a ball mill, to attain the appropriate homogeneity and viscosity for tape casting. A double doctor blade was used to control the thickness. Thermogravimetric and dilatometric analysis were performed to find the optimized heat treatment to remove the organics and densify the electrolyte while keeping a porous anode. The half-cells were then calcined and sintered at 1450°C/1h, with low heating and cooling rates to prevent cracks due to the different thermal expansion of the layers. The LSM cathode was then deposited by spin-coating and attached to the half-cell at 1100°C/1h. To verify the adhesion, thickness, and porosity of the layers, the sample was analyzed by scanning electron microscope. The electrochemical performance was evaluated by impedance spectroscopy and single cell tests under hydrogen and synthetic air. In this study we demonstrate a facile route to SOFC fabrication by co-casting and co-sintering, with relatively mild sintering conditions, with a good control of layer thickness, porosity and adhesion. Figure 1

Development of Anode-Supported Solid Oxide Fuel Cell by Sequential Tape-Casting and Co-Sintering

Simple and cost-effective technologies to produce solid oxide fuel cells require control of microstructure, thickness, homogeneity, and reproducibility of the functional layers. The manufacturing of a solid oxide fuel cell (SOFC) involves significant ceramic processing challenges to obtain layers with controlled microstructure. Possibly the most common technique for large-scale production of SOFCs is tape casting. In this study, YSZ electrolyte and 60NiO/YSZ anode slurries were studied for the production of half-cells deposited by the sequential tape casting technique. A co-sintering procedure was developed for the half-cells and after cathode deposition the single cells were tested.

Processing Ceramic Proton Conductor Membranes for Use in Steam Electrolysis.

Steam electrolysis constitutes a prospective technology for industrial-scale hydrogen production. The use of ceramic proton-conducting electrolytes is a beneficial option for lowering the operating temperature. However, a significant challenge with this type of electrolyte has been upscaling robust planar type devices. The fabrication of such multi-layered devices, usually via a tape casting process, requires careful control of individual layers’ shrinkages to prevent warping and cracks during sintering. The present work highlights the successful processing of 50 × 50 mm2 planar electrode-supported barium cerium yttrium zirconate BaZr0.44Ce0.36Y0.2O2.9 (BZCY(54)8/92) half cells via a sequential tape casting approach. The sintering parameters of the half-cells were analyzed and adjusted to obtain defect-free half-cells with diminished warping. Suitably dense and gas-tight electrolyte layers are obtained after co-sintering at 1350 °C for 5 h. We then assembled an electrolysis cell using Ba0.5La0.5CoO3−δ as the steam electrode, screen printed on the electrolyte layer, and fired at 800 °C. A typical Ba0.5La0.5CoO3−δ|BaZr0.44Ce0.36Y0.2O3−δ(15 μm)|NiO-SrZr0.5Ce0.4Y0.1O3−δ cell at 600 °C with 80% steam in the anode compartment reached reproducible terminal voltages of 1.4 V @ 500 mA·cm−2, achieving ~84% Faradaic efficiency. Besides electrochemical characterization, the morphology and microstructure of the layered half-cells were analyzed by a combination of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy. Our results also provide a feasible approach for realizing the low-cost fabrication of large-sized protonic ceramic conducting electrolysis cells (PCECs).

Asymmetric LSCF Membranes Utilizing Commercial Powders.

Powders of constant morphology and quality are indispensable for reproducible ceramic manufacturing. In this study, commercially available powders were characterized regarding their microstructural properties and screened for a reproducible membrane manufacturing process, which was done by sequential tape casting. Basing on this, the slurry composition and ratio of ingredients were systematically varied in order to obtain flat, crack-free green tapes suitable for upscaling of the manufacturing process. Debinding and sintering parameters were adjusted to obtain defect-free membranes with diminished bending. The crucial parameters are the heating ramp, sintering temperature, and dwell time. The microstructure of the asymmetric membranes was investigated, leading to a support porosity of approximately 35% and a membrane layer thickness of around 20 µm. Microstructure and oxygen flux are comparable to asymmetric La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) membranes manufactured from custom-made powder, showing an oxygen flux of > 1 mL⋅cm−2⋅min at 900 °C in air/Ar gradient.

Influence of support layer resistance on oxygen fluxes through asymmetric membranes based on perovskite-type oxides SrTi1-xFexO3-δ

Asymmetric membranes of mixed ionic-electronic conducting perovskite-type oxides SrTi1-xFexO3-δ (STF, x = 0.3, 0.5 and 0.7) were prepared by inverse sequential tape-casting. Both porous support (~600 μm) and functional membrane layer (~20 μm) for a given membrane assembly were made from the same composition to ensure thermochemical compatibility between the layers. Oxygen fluxes were assessed in the range 650 -1020 °C, using either (non-pressurized) ambient air or pure oxygen as feed gas at the support side of the asymmetric membrane and argon as sweep gas. Notably, similar oxygen fluxes (~1.2 × 10−6 mol cm−2 s−1) are measured through the membranes of different compositions above 950 °C when using ambient air as feed gas. This observation is interpreted to reflect the major role of the support layer resistance in rate-limiting the oxygen fluxes through the STF asymmetric membranes, which conclusion is supported by comparison of the oxygen fluxes with those measured previously through asymmetric membranes of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF). A simple diffusion-convection model is used to account for the observed gas phase polarization in the porous support layers limiting the oxygen fluxes.

Lanthanum tungstate membranes for H2 extraction and CO2 utilization: Fabrication strategies based on sequential tape casting and plasma-spray physical vapor deposition

In the context of energy conversion efficiency and decreasing greenhouse gas emissions from power generation and energy-intensive industries, membrane technologies for H2 extraction and CO2 capture and utilization become pronouncedly important. Mixed protonic-electronic conducting ceramic membranes are hence attractive for the pre-combustion integrated gasification combined cycle, specifically in the water gas shift and H2 separation process, and also for designing catalytic membrane reactors. This work presents the fabrication, microstructure and functional properties of Lanthanum tungstates (La28−xW4+xO54+δ, LaWO) asymmetric membranes supported on porous ceramic and porous metallic substrates fabricated by means of the sequential tape casting route and plasma spray-physical vapor deposition (PS-PVD). Pure LaWO and W site substituted LaWO were employed as membrane materials due to the promising combination of properties: appreciable mixed protonic-electronic conductivity at intermediate temperatures and reducing atmospheres, good sinterability and noticeable chemical stability under harsh operating conditions. As substrate materials porous LaWO (non-substituted), MgO and Crofer22APU stainless steel were used to support various LaWO membrane layers. The effect of fabrication parameters and material combinations on the assemblies’ microstructure, LaWO phase formation and gas tightness of the functional layers was explored along with the related fabrication challenges for shaping LaWO layers with sufficient quality for further practical application. The two different fabrication strategies used in the present work allow for preparing all-ceramic and ceramic-metallic assemblies with LaWO membrane layers with thicknesses between 25 and 60 μm and H2 flux of ca. 0.4 ml/min cm2 measured at 825 °C in 50 vol% H2 in He dry feed and humid Ar sweep configuration. Such a performance is an exceptional achievement for the LaWO based H2 separation membranes and it is well comparable with the H2 flux reported for other newly developed dual phase cer-cer and cer-met membranes.

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.

Stability and sintering of MgO as a substrate material for Lanthanum Tungstate membranes

The performance of ceramic gas separation membranes can be increased by reducing their thickness. To maintain the mechanical stability of the membrane, a supporting structure is needed. In this work magnesium oxide (MgO) is identified as support material for H2-separation membranes made of La6-xWO12-δ (LaWO). Therefore MgO is tested under application-related conditions in a water-gas-shift (WGS) catalytic membrane reactor for hydrogen production and shows a good stability. The sequential tape casting serves as the manufacturing method for the preparation of the asymmetric membrane structures. To show the compatibility of the two materials, detailed investigations of the sintering behaviour and stability tests are performed and show the well-matching properties of the two materials. Microstructural analyses reveal the inter-diffusion between LaWO and MgO.

Solid Oxide Fuel Cell, Stack and System Development Status at Forschungszentrum Jülich

Based on more than 20 years of scientific development, Forschungszentrum Jülich is still continuously improving its SOFC technology. Based on a warm pressing process, anode supported cells have been tested in stack sizes up to 5 kW. Recent cell developments focused on tape-casting and sequential tape-casting. The enhanced thermo-mechanical robustness of stacks in the kW range was demonstrated by successfully cycling 100 times between 200 and 700 °C. To be able to utilize also anode supported cells from other manufacturers, the design was modified to a window frame layout, integrating four 10×10 cm² cells in one layer. A 20 kW system was operated for about 7000 hours in total, demonstrating thereby the suitability of the module and system concept developed in JÜLICH. As special highlights, long-term tests with short stacks have now reached operation times of 65,200 h and 34,500 h, respectively. As relatively new subject the activities in high temperature electrolysis are briefly outlined.

Towards the fabrication of La0.98−xSrxCo0.2Fe0.8O3−δ perovskite-type oxygen transport membranes

La0.98−xSrxCo0.2Fe0.8O3−δ (LSCF) is a candidate material for use as an oxygen transport membrane (OTM). In this work, fabrication-relevant properties (sinteringbehaviour, thermal and chemical expansion) of LSCF (x = 0.2, 0.4, 0.6, 0.8) were investigated in order to select the preferred composition for fabricating a thin-film supported membrane able to withstand the thermochemical stresses encountered during manufacturing and operation with simultaneously high oxygen permeation flux. Partial substitution of La by Sr ions in LSCF is beneficial for increasing the oxygen permeation rate, but it causes drawbacks regarding manufacturing and operation. A Sr content of x ≥ 0.6 results in a swelling of the material during sintering, which complicates the manufacturing of thin, leak-free membranes. This swelling is related to oxygen release during heating, combined with the formation of a liquid phase above 1200 ◦C. Furthermore, an increase in total strain with Sr content is observed. This is caused by the chemical expansion, while there is no significant change in thermal expansion with increasing Sr content. The compositions x = 0.4 and x = 0.6 showed tolerable expansion coefficients as well as adequate sintering behaviour and were therefore selected for the fabrication of thin supported membranes. These supported membranes with a thickness of 30 m were manufactured by sequential tape casting and characterised regarding microstructure and oxygen flux.

Oxygen permeation through tape-cast asymmetric all-La0.6Sr0.4Co0.2Fe0.8O3−δ membranes

One of the most promising materials for oxygen separation amongst ceramic oxygen transport membranes (OTMs) is La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) due to its relatively high oxygen permeability combined with high stability. In this work, asymmetric thin-film LSCF membranes supported over a porous LSCF support were manufactured by inverse sequential tape casting. Moreover, surface activation was accomplished by depositing a porous LSCF activation layer in order to promote oxygen evolution reaction, i.e. O2− to O2 oxidation, in the permeate membrane side. In this case, the porous layer allows the surface area available for oxygen activation to be enlarged. Both the manufacturing of the asymmetric thin-film membranes and the surface activation are described in detail. A thorough study of the oxygen permeation is presented for disk-shaped 30µm thick LSCF-supported membranes considering the following operating parameters: temperature (1000–600°C), sweep flow rate (300–750mlmin−1 argon) and oxygen partial pressure in the feed (0.21–1atm). High permeation fluxes were achieved, e.g., 11.87mlmin−1cm−2 at 1000°C and 300mlmin−1 argon sweep when using pure oxygen as feed. A change in the apparent activation energy at about 850ºC was related to a reversible structural change in the perovskite symmetry (cubic↔rhombohedral), as revealed by XRD measurements. Furthermore, the application of an activation layer allowed the permeation process to be improved, especially at low temperatures, i.e. below 800°C. Specifically, an improvement of up to about 300% at 600°C is observed upon application of the activation layer. The activated membrane reached a flux of 13.3mlmin−1cm−2 at 1000°C under an O2/Ar gradient. Additional permeation tests using CO2-rich sweep gas demonstrated the good stability and performance of these LSCF asymmetric membranes at 900 and 1000ºC.

Direct lamination of solid oxide fuel cell anode support, anode, and electrolyte by sequential tape casting of thermoreversible gel slips

A novel direct lamination technique by tape casting thermoreversible gel-based slips is introduced for the production of solid oxide fuel cell anode support, anode, and electrolyte layers. Production of cells with controlled layer thicknesses of ∼10–500 μm and having well formed and relatively high toughness interfaces is demonstrated. Cells with maximum current density of 1.76 A·cm−2 and maximum power density 425 mW cm−2 were achieved using 97% H2/3% H2O fuel at 800 °C. Specific opportunities for further optimization of processing to improve electrochemical performance are highlighted.

Tape Casting as a Multi Purpose Shaping Technology for Different Applications in Energy Issues

Tape casting is widely used in industrial scale for production of multilayer ceramic capacitors or substrates for different applications. In 2009, it was successfully introduced as standard shaping technology for 3 (BSCF) are shown. The entire scope from the preparation of the used powders, the different manufacturing steps and their optimization potential up to the final tape-cast product will be discussed. The influence of the use of pore forming agents, heat treatment or other parameters during processing will be described in detail. Finally, the option of sequential tape casting of different materials for graded structures as a future step in shaping technology will be presented for different applications.

Sintering and Deformation of Solid Oxide Fuel Cells Produced by Sequential Tape Casting

Anode‐supported solid oxide fuel cells have been produced by water base sequential tape casting and cosintering. The curvature developed upon cosintering was monitored in situ. By tailoring the green microstructure, it was possible to reduce the curvature rate and to produce flat cells avoiding the need for a creep‐flattening treatment. The power density at 800°C and 0.7 V was 751.7 mW/cm2.

Effect of Al and Ce doping on the deformation upon sintering in sequential tape cast layers for solid oxide fuel cells

Water-based tape casting is an attractive production route for planar solid oxide fuel cells (SOFCs) due to its high productivity and reduced environmental issues. In this work planar anode supported SOFCs with thin electrolyte were prepared by water-based sequential tape casting and co-sintering. An in situ high temperature monitoring apparatus was assembled to allow the determination of free sintering shrinkage of thin green tape cast layers and to follow the curvature developed in multilayers during the entire sintering process. The instantaneous curvature developed upon co-sintering was studied as a function of the firing schedule and layer composition. It was found that by tailoring the electrode composition it is possible to reduce the shrinking rate difference between anode and electrolyte thus obtaining defect-free electrolyte, minimising the residual curvature of the half-cell and improving the electrochemical performances of the cell.