Performance of Solid Oxide Fuel Cells with Controlled Microstructure of Anode Substrate

Present results on intermediate temperature-operating solid oxide fuel cells (IT-SOFC) are mainly focused to obtain higher performance of single cell at lower operating temperature, especially with planar type. In order to develop a 1 kW-class SOFC system for Residential Power Generation (RPG) application that can be operated at intermediate temperatures, we have developed an anode-supported and planar type SOFC stack using cost-effective interconnects such as ferritic stainless steels. To improve electrical performance of the anode-supported SOFC, cells with alternative electrode or thin electrolyte layer of YSZ and ScSZ, respectively, were fabricated by slurry coating and their performances were investigated. Mixtures of NiO and 8YSZ powders were pressed into rectangular plates, which were pre-sintered at 1400°C for 1 h. Then the 8YSZ (8mol%Y2O3+ZrO2) or 10ScSZ (10mol%Sc2O3+1 mol%CeO2+ZrO2) electrolytes were coated by slurry coating method on the upper side of anode substrate and cofired at 1550 or 1500°C for an hour. Thereafter, composite cathode pastes of LSM (La0.7Sr0.2MnO3) or LSCF ((La0.6Sr0.4)(Co0.2Fe0.8)O3 ) were screen-printed on thin electrolytes and heat-treated at 1100°C for 2 h. The final size of anode-supported single cell sintered was about 5 × 5 cm2, and the thickness of the electrolyte and the cathode layer was about 20 μm and 30 μm, respectively. The I-V and AC impedance characteristics of these single cells were evaluated at intermediate temperature (650 ∼ 750°C) using hydrogen gas as a fuel. The maximum power density of anode-supported cell was 0.4 ∼ 1.7 W/cm2 at 750°C and 0.12 ∼ 0.55 W/cm2 at 650°C depending on the composition and microstructure of electrolyte/electrodes.

La0.8Sr0.2Co0.8Fe0.2O3 (LSCF) nanopowders, which are being investigated as a promising cathode material for low-temperature solid oxide fuel cells (SOFCs), were synthesized by citric acid gel combustion method. The LSCF nanopowders synthesized at 700°C are single perovskite phases and have an average particle size of less than 30 nm. In order to evaluate the use of the synthesized LSCF nanopowders as cathode material of low-temperature SOFCs, anode-supported SOFCs were fabricated from the synthesized LSCF nanopowders and tested in the conditions of humidified hydrogen for anode and oxygen for cathode. The anode-supported single cell with the LSCF cathode sintered at 700°C showed high electrical performance with the maximum power density of 771 mW cm−2 at 600°C. The results show that the synthesized LSCF nanopowders are suitable to be applied as cathode material for low-temperature SOFCs.

In this study, the performance of anode-supported and electrolyte-supported cells was compared under similar operating conditions for direct ammonia-fueled solid oxide fuel cell (SOFC); the cell configuration of both types of cells was as follows, Ni‒YSZ|YSZ|GDC|LSCF. The anode-supported cell showed better performance as compared with that of the electrolyte-supported cell. A power density of ca. 0.358 W cm-2 was achieved for the anode-supported cell at 700 oC, which was higher than that of the electrolyte-supported cell. Furthermore, the ohmic and polarization resistances were lower for anode-supported cell. This is because in the anode-supported cell, the thinner electrolyte layer is responsible for the reduced ohmic resistance and improved cell efficiency. The effect of humidity on the performance of both types of cells using NH3 and H2 fuels was studied. The experimental results indicated that in the case of ammonia fuel, a small amount of humidity (1.67% H2O) was beneficial for better performance. However, further increase in humidity caused cell performance degradation. The effect of humidity on the cell performance was further analyzed. The anode microstructure of both types of cells was investigated after 10 h of discharge operation at 0.2 A cm-2 at 700 oC using NH3 and H2 fuels under various humidified conditions. For the anode-supported cell, the surface of Ni particles was covered with the small-sized particles after discharge operation; the Ni particles on the anode surface coarsened significantly in the ammonia fuel as compared with the hydrogen fuel. This is because the anode surface is exposed to the gaseous mixture containing large amount of ammonia which may cause the nitridation of Ni particles. On the other hand, at the anode/electrolyte interface the extent of coarsening of Ni particles was almost similar regardless of the fuel. This can be explained by the fact that most of the NH3decomposes catalytically and thermally at the anode surface. Hence, the partial pressure of ammonia will be lower at the anode/electrolyte interface. In this study, it was found that the anode-supported design is suitable for direct-ammonia fueled SOFCs. In the case of anode-supported cells, the improvement in the performance and the stability can be expected by optimizing the operating conditions, such as the operating temperature and the steam concentration in the inlet gas. Acknowledgement This work was supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “energy carrier” (Funding agency: JST).

Solid oxide fuel cells (SOFCs) have garnered significant attention as a promising technology for clean and efficient power generation due to their ability to utilise renewable fuels such as hydrogen and ammonia. As carbon-free energy carriers, hydrogen and ammonia are expected to play a pivotal role in achieving net-zero emissions. However, a critical research question remains: how does the electrochemical performance of SOFCs compare when fuelled by hydrogen vs. ammonia, and what are the implications for their practical application in power generation? This mini-review paper is premised on the hypothesis that while hydrogen-fuelled SOFCs currently demonstrate superior stability and performance at low and high temperatures, ammonia-fuelled SOFCs offer unique advantages, such as higher electrical efficiencies and improved fuel utilisation. These benefits make ammonia a viable alternative fuel source for SOFCs, particularly at elevated temperatures. To address this, the mini-review paper provides a comprehensive comparative analysis of the electrochemical performance of SOFCs under direct hydrogen and ammonia fuels, focusing on key parameters such as open-circuit voltage (OCV), power density, electrochemical impedance spectroscopy, fuel utilisation, stability, and electrical efficiency. Recent advances in electrode materials, electrolytes, fabrication techniques, and cell structures are also highlighted. Through an extensive literature survey, it is found that hydrogen-fuelled SOFCs exhibit higher stability and are less affected by temperature cycling. In contrast, ammonia-fuelled SOFCs achieve higher OCVs (by 7%) and power densities (1880 mW/cm2 vs. 1330 mW/cm2 for hydrogen) at 650 °C, along with 6% higher electrical efficiency. Despite these advantages, ammonia-fuelled SOFCs face challenges such as NOx emissions, nitride formation, environmental impact, and OCV stabilisation, which are discussed alongside potential solutions. This mini review aims to provide insights into the future direction of SOFC research, emphasising the need for further exploration of ammonia as a sustainable fuel alternative.

Research into the use of Rh and Ce0.80Gd0.20O1.90 (CGO20) co-impregnated La0.20Sr0.25Ca0.45TiO3 (LSCTA-) anodes for electrolyte-supported Solid Oxide Fuel Cells (SOFC) has yielded extremely impressive durability and robustness at industrial short stack scales over the past decade. These anodes have exhibited the ability to rival the degradation and RedOx/thermal/thermo-RedOx cycling tolerance of state-of-the-art SOFC anodes at short stack scales, in addition to providing the ability to operate under sulfur-laden fuel gas streams and high fuel utilisation/overload conditions. (1)Given the success of implementation of LSCTA- anodes into Electrolyte Supported Cells (ESC) and the reasonable mechanical strength of LSCTA- as a support material, (2,3) successful attempts have also been made to employ LSCTA- as an anode support for SOFC at button cell scales, (4,5) in addition to appraisal of the upscaling of thick-film ceramic processing techniques used to prepare larger (20 cm by 20 cm) SOFC anode supports. (3) These studies performed by Lu et al., Ni et al. and Verbraeken et al. (3-5) focussed upon production of LSCTA- anode supports by aqueous tape casting followed by either co-casting or screen printing of a 8 mol. % yttria-stabilised-zirconia (8YSZ) electrolyte layer.Therefore, using these studies as a basis for the current research, we present results concerning the ceramic processing of Anode Supported Cells (ASC) that employ LSCTA- anode ‘backbone’ microstructures, with the ultimate aim of testing SOFC whose anodes have been decorated with Rh and CGO20 catalysts through wet impregnation. Here, we detail a thermal compatibility study of a variety of electrode and electrolyte material sets using dilatometric analysis, leading to the conclusion that the shrinkages of LSCTA- and 8YSZ are sufficiently matched to allow co-sintering of the anode support and electrolyte layers. Subsequently, the thick-film aqueous ceramic processing of LSCTA- anode supports, via tape casting, is discussed in addition to an appraisal of the most appropriate method to produce dense 8YSZ electrolyte layers (i.e., electrolyte deposition by co-casting or screen printing), with the aim of co-sintering the structure up to 1400 °C in air. Finally, an evaluation of the microstructural characteristics of LSCTA − supports, prepared using a typical graphite pore former (commonly used with organic solvent systems) or without the use of a pore former, will be provided, in comparison to microstructures resulting from the incorporation of poly(ethyl/methyl methacrylate) pore formers that are compatible with the aqueous solvent system employed. References R. Price, M. Cassidy, J. G. Grolig, G. Longo, U. Weissen, A. Mai and J. T. S. Irvine, Adv. Energy Mater., 2003951, 1 (2021).V. Vasechko, M. Ziegner and J. Malzbender, Ceram. Int., 40, 13179 (2014).M. C. Verbraeken, B. R. Sudireddy, V. Vasechko, M. Cassidy, T. Ramos, J. Malzbender, P. Holtappels and J. T. S. Irvine, J. Eur. Ceram. Soc., 38, 1663 (2018).L. Lu, C. Ni, M. Cassidy and J. T. S. Irvine, J. Mater. Chem. A, 4, 11708 (2016).C. Ni, L. Lu, D. N. Miller, M. Cassidy and J. T. S. Irvine, J. Mater. Chem. A, 6, 5398 (2018).

Mixed oxygen ion and electron-conducting materials are viable cathodes for solid oxide fuel cells due to their excellent oxygen transport kinetics and mixed electrical conductivity, which ensure highly efficient operation at low and medium temperatures. However, iron-based double perovskite oxides usually exhibit poor electrocatalytic activity due to low electron and oxygen ion conductivity. In this paper, Ca is doped in PrBaFe2O5+δ A-site to improve the electrochemical performance of PrBaFe2O5+δ. Results show that replacing Pr with Ca does not change the crystal structure, and the Ca doping effectively increases the adsorbed oxygen content and accelerates the migration and diffusion rate of O2- to the electrolyte|cathode interface. The polarization resistance of the symmetric cell PC0.15BF|CGO|PC0.15BF is 0.033 Ω·cm2 at 800 °C, which is about 56% lower than that of PBF, confirming the enhancement of the mixed conduction of oxygen ions and electrons. In addition, the anode-supported single cell has a peak power density of 512 mW·cm-2 at 800 °C.

To improve the performance of the anode-supported Solid Oxide Fuel Cells (SOFCs) which can be operated at an intermediate temperature, the functional layer (FL) is introduced on a Ni- YSZ anode substrate. And the scandia-stabilized zirconia (ScSZ) and the samaria-doped ceria (SDC) which have the high ionic conductivity and the chemical stability as well as the yttria- stabilized zirconia (YSZ) are used as material for the anode FL with the Ni. The fabrication process of anode-supported single cell with the anode FL was established and the power density of those was appreciated. As a result, the sample with anode FL (Ni-YSZ) has higher power density than normal cell. The single cell which was consist of the FL(Ni-YSZ) and a electrolyte(YSZ) showed about 550mW/cm2 as the maximum power density and 0.41Ω cm2 as a lower internal resistance at 650{degree sign}C. In case of the single cell using the ScSZ and the SDC as the anode FL, the performance of samples decrease rapidly and those showed unstable voltages during long-term test.

Microtubular anode-supported solid oxide fuel cells (μt-SOFC) were created with a metallic coil embedded in the anode to act as current collector. The electrochemical performance was experimentally examined by comparing the power density (PD) of μt-SOFC with embedded coils of different turns per unit length and composition (nickel and palladium). It is shown that an increase in the turns per unit length results in a proportional current density increase and in a quadratic increment of PD. Additional performance improvement is found for the cell with palladium current collector due to the higher catalytic activity for hydrogen oxidation.

This report summarizes the results of Phase II of this program, 'Low-Cost Manufacturing Of Multilayer Ceramic Fuel Cells'. The objective of the program is to develop advanced ceramic manufacturing technologies for making planar solid oxide fuel cell (SOFC) components that are more economical and reliable for a variety of applications. Phase II development work focused on three distinct manufacturing approaches (or tracks) for planar solid oxide fuel cell elements. Two development tracks, led by NexTech Materials and Oak Ridge National Laboratory, involved co-sintering of planar SOFC elements of cathode-supported and anode-supported variations. A third development track, led by the University of Missouri-Rolla, focused on a revolutionary approach for reducing operating temperature of SOFCs by using spin-coating to deposit ultra-thin, nano-crystalline YSZ electrolyte films. The work in Phase II was supported by characterization work at Ohio State University. The primary technical accomplishments within each of the three development tracks are summarized. Track 1--NexTech's targeted manufacturing process for planar SOFC elements involves tape casting of porous electrode substrates, colloidal-spray deposition of YSZ electrolyte films, co-sintering of bi-layer elements, and screen printing of opposite electrode coatings. The bulk of NexTech's work focused on making cathode-supported elements, although the processes developed at NexTech also were applied to the fabrication of anode-supported cells. Primary accomplishments within this track are summarized below: (1) Scale up of lanthanum strontium manganite (LSM) cathode powder production process; (2) Development and scale-up of tape casting methods for cathode and anode substrates; (3) Development of automated ultrasonic-spray process for depositing YSZ films; (4) Successful co-sintering of flat bi-layer elements (both cathode and anode supported); (5) Development of anode and cathode screen-printing processes; and (6) Demonstration of novel processes for composite cathode and cermet anode materials. Track 2--ORNL's development work focused solely on making anode-supported planar cells by tape casting of a porous anode substrate, screen printing of a YSZ electrolyte film, co-sintering of the bi-layer element, and screen-printing of an opposite cathode coating. Primary accomplishments within this track are summarized below: (1) Development and scale-up of anode tape casting and lamination processes; (2) Development of proprietary ink vehicle for screen-printing processes; (3) Development of screen-printing process for depositing YSZ films; (4) Successful co-sintering of flat bi-layer anode-supported elements; and (5) Development of cathode screen-printing process. Track 3--UMR's process development work involved fabrication of a micro-porous cathode substrate, deposition of a nano-porous interlayer film, deposition of nano-crystalline YSZ electrolyte films from polymeric precursor solutions, and deposition of an anode coating. Primary accomplishments within this track are summarized below: (1) Development and scale up of tape casting and sintering methods for cathode substrates; (2) Deposition of nano-porous ceria interlayer films on cathode substrates; (3) Successful deposition of dense YSZ films on porous cathode substrates; and (4) Identification of several anode material options.

The objective of this work was to investigate how fuel utilization and method of fuel delivery for a large planar fuel cell with co-flow configuration will affect the degradation rate and mechanism of phosphine poisoning of a solid-oxide fuel cell (SOFC). Coal syngas, a potential fuel source for SOFCs, contains gas phase impurities such as PH3, which rapidly degrade Ni-based SOFC anodes. Researchers have shown significant reconstruction of Ni-anodes in button cell configurations with ~0.5 mV hr-1 degradation rates, but it is not evident that these rates will occur in actual stack applications. A singular planar stack repeat unit was constructed using a Haynes 242 interconnect manifold with a cobalt-oxide coating. The cell was operated at 800°C with 10 ppm PH3 in dry H2. Cell performance was evaluated over 500 hours by means of voltage-current measurements and impedance spectroscopy. PH3 was measured entering the fuel cell and then exiting the fuel cell in the exhaust. The post-run material analysis of the contaminated cell was conducted via x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and scanning electron micrographs (SEM). In this work, there was no appreciable degradation attributable to PH3 poisoning of the anode. No reconstruction of the Ni-anode was observed. This result is in contrast to the many papers published on the subject, where anode-supported SOFC in a button cell configuration degraded rapidly. It is believed that the increased fuel utilization of the large planar cell compared to the published literature using button cells contributed to increased H2O generation which led to side reactions that prevented the phosphorus from interacting with the Ni-anode; platinum components may have catalyzed these reactions.

Gadolinium-doped ceria (GDC) is widely recognized as an effective diffusion barrier layer in solid oxide fuel cells (SOFCs) due to its ability to prevent undesirable chemical reactions. However, the high sintering temperatures required for GDC densification often lead to the formation of a Ce-Zr solid solution phase, which compromises the long-term stability and performance of SOFCs. To address these issues, this study investigates a new ternary-doped ceria composition, Ce(Gd, Bi, Yb)O2-δ(GYBC), as an alternative diffusion barrier layer material. The GYBC layer was fabricated using ultrasonic spray coating, producing a thin, dense layer with optimal microstructural properties. When applied in a SOFC unit cell (Ni-YSZ/YSZ/GYBC/La0.4Sr0.6Co0.2Fe0.8O3-δ (LSCF)-GDC/LSCF), the GYBC layer showed a significant improvement in electrochemical performance. The SOFC unit cell achieved a power density of 2.32 W cm-2 at an operating temperature of 800 °C, which is higher than cells that use a conventional GDC diffusion barrier layer. This improvement is attributed to the high oxygen storage capacity (OSC) of the GYBC layer, which enhances oxide ion supply at the cathode/electrolyte interface and substantially boosts performance under the high current conditions typical of practical SOFC applications. These results suggest that GYBC has the potential as a diffusion barrier material for SOFCs, improving their performance and durability.

Integrated gasification fuel cell (IGFC) systems combining coal gasification and solid oxide fuel cells (SOFC) are promising for highly efficient and environmentally friendly utilization of coal for power production. Most IGFC system analyses performed to-date have used nondimensional thermodynamic SOFC models that do not resolve the intrinsic constraints of SOFC operation. In this work a quasi-two-dimensional (2D) finite volume model for planar SOFC is developed and verified using literature data. Special attention is paid to making the model capable of supporting recent SOFC technology improvements, including the use of anode-supported configurations, metallic interconnects, and reduced polarization losses. Activation polarization parameters previously used for high temperature electrolyte-supported SOFC result in cell performance that is much poorer than that observed for modern intermediate temperature anode-supported configurations; thus, a sensitivity analysis was conducted to identify appropriate parameters for modern SOFC modeling. Model results are shown for SOFC operation on humidified H2 and CH4 containing syngas, under coflow and counterflow configurations; detailed internal profiles of species mole fractions, temperature, current density, and electrochemical performance are obtained. The effects of performance, fuel composition, and flow configuration of SOFC performance and thermal profiles are evaluated, and the implications of these results for system design and analysis are discussed. The model can be implemented not only as a stand-alone SOFC analysis tool, but also a subroutine that can communicate and cooperate with chemical flow sheet software seamlessly for convenient IGFC system analysis.

A systematic study was initiated of anode-supported solid oxide fuel cells (SOFCs) with Nd2NiO4 cathodes. This type of cathode, a mixed conducting K2NiF4-type material, can be considered as a candidate for SOFC applications. In this study, the influence of (1) the presence of a Ce0.8Gd0.2O1.9 (CGO) interlayer between the electrolyte and the cathode, (2) sintering conditions, and (3) the grain size of the powder on the performance of SOFCs with Nd2NiO4 cathodes was investigated in more detail. Results from current density-voltage characteristics and permeation and gas diffusion measurements showed that the electrochemical performance was promising for SOFCs including a CGO interlayer and a Nd2NiO4 cathode (prepared with a powder with a d50 of 0.5A∕cm2 or 0.8μm) sintered at 1100°C or higher; current density at 800°C and 700mV between 1.2 and 1.3A∕cm2. The microstructure of the cathode was such that no gas diffusion problems occurred.

1.Introduction Solid oxide fuel cells (SOFCs) have received much attention as promising electrochemical power generation devices because of their high electrical efficiency and environment adaptability. Development of SOFCs is now focused on lowering the operating temperature from the conventional range of 750-900°C to an intermediate range of 500-700ºC, allowing a wider range of materials for SOFC components and improvement of thermal reliability. Preparing the Yttlia Stabilized Zirconia (YSZ) and Gadolinia-doped ceria (GDC)) bilayer electrolytes are effective for reducing operating temperature [1]. In the present work, NiO-YSZ anode supported cells with YSZ/GDC bilayer electrolytes and (La,Sr) (Co,Fe) O3 (LSCF) thin film cathodes were fabricated by pulsed laser deposition (PLD) and screen printing. However, one thermal cycle test of a cell between 200°C and 600°C, with heating and cooling rates of 400°C /h, resulted in detachment of the LSCF thin film and thus reduced durability. To improve the adhesion between the LSCF and GDC, (La,Sr)CoO3(LSC), nano particles were deposited on the GDC thin films by PLD. This step was expected to increase contact area between electrolyte and cathode. We investigated the influence of the LSC nano particle on thermal reliability and I-V characteristic of SOFCs. 2.Experimental Details NiO-YSZ cermet (NiO:YSZ＝60:40 wt%, 500 μm thick) was used as the anode substrate, YSZ (8 mol% Y2O3) and GDC (10 mol% GdO2) as electrolyte materials, and La0.6Sr0.4Co0.2Fe0.8 (LSCF) and La0.6Sr0.4Co (LSC) as cathode materials. YSZ (8 μm thick) and LSCF (30 μm thick) films were prepared by screen printing and GDC (3 μm thick) was deposited by PLD. Two sets of unit cells were prepared: one set was with LSC nano particles deposited between GDC and LSCF thin films by PLD (NiO-YSZ / YSZ / GDC / LSC particle / LSCF) and the other set was without LSC nano particles (NiO-YSZ / YSZ / GDC / LSCF).Thermal cycle test between 200 and 600°C with heating and cooling rates of 400° C /h were performed. Power densities and I-V characteristics were measured. 3.Results (a) Deposition of LSC nano particles by PLD on the GDC thin film. Figure 1 shows a scanning electron microscopy image of the surface of a GDC thin film. Many LSC nano particles (50-nm diameter) were deposited on the dense GDC thin film by PLD, which increased the area of contact between the GDC and LSCF thin films. (b) Thermal cycle test of NiO-YSZ anode supported cells with or without LSC nano particles. Two types of unit cells, (1) NiO-YSZ / YSZ / GDC / LSC particle / LSCF and (2) NiO-YSZ / YSZ / GDC / LSCF were prepared by screen printing and PLD. Photographs of unit cells after one thermal cycle are shown in Fig. 2. It is evident that adding the LSC nano particles succeeded in suppressing detachment of the LSCF thin film. Spike effect resulted in high adhesion between LSCF and GDC. The unit cell with LSC nano particles survived 50 thermal cycles and yielded higher thermal reliability. (c) I-V characteristics of NiO-YSZ anode supported cells with or without LSC nano particles. Figure 3 shows the I-V characteristics of unit cells with and without LSC nano particles. The maximum power densities of unit cells with or without LSC nano particles were 0.5 and 0.3 W·cm-2, respectively. Cell performances were found to be better when LSC nano particles were deposited, because of increase in reactive sites.[1] T. Mukai et al., Journal of Fuel Cell Science and Technology , 10(2013) 061006-1-6.

Development of 1 kW class solid oxide fuel cell stack using anode-supported planar cells