Development and testing of anode-supported solid oxide fuel cells with slurry-coated electrolyte and cathode

In recent years, anode-supported solid oxide fuel cell (SOFC) technology gains greater attention. Kinetic and thermodynamic parameters play a pivotal role in influencing the overall efficiency and functionality of SOFCs. In present study, 3D model of a single cell anode-supported SOFC is developed using ANSYS fluent. Kinetic and thermodynamic parameters are optimized by comparison with experimental data. Optimized parameters are subsequently used to investigate the impact of pressure and fuel utilization on the overpotential. Simulation results indicate that optimized parameters give rise to an increased fuel consumption and hence water formation. This can be explained by the fact that optimized parameters give rise to an increased rate of reaction. Optimized parameters lead to a reduction in cell overpotential thereby increasing current and power densities at elevated pressure. Increased fuel utilization correlates with a decrease in power and current densities.

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.

In this chapter, the construction, principle of operation, types and production technologies of SOFCs are presented and characterized. Three main types of SOFC are described according to the type of support layer responsible for the mechanical strength of the cell: electrolyte-supported solid oxide fuel cells (ES-SOFC), anode-supported solid oxide fuel cells (AS-SOFC), and metal-supported solid oxide fuel cells (MS-SOFC). Base and raw materials for particular functional layers of solid oxide fuel cells are characterized, i.e., anode, electrolyte, and cathode layers. Thick- and thin-film technologies for the production of particular elements of SOFC fuel cells are presented. Using the example of technology developed in the Institute of Power Engineering Ceramic Department CEREL, the production technology of anode-supported solid oxide fuel cells and the method of characterizing the microstructure and electrochemical properties of the produced cells are presented.

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.

Solid oxide fuel cells (SOFCs), as highly efficient energy conversion devices, are anticipated to play a significant role in the realization of a low-carbon society. ENE-FARM type S (EF), equipped with SOFC stack, has been commercialized since 2012 by Osaka Gas. To further expand the market of EF, higher electrical efficiency, higher durability, lower cost of SOFC stack, and downsizing of EF are needed. For realizing these issues, two model changes were conducted in 2016 and 2020. The SOFC stack installed in the current EF, which is composed of Anode-supported SOFC (ASC), has established durability of over 12 years. For further widespread adoption in the EF market, we have focused on Metal-supported SOFCs (MSC), which have the potential to reduce costs by using fewer expensive ceramics.However, the use of a metal substrate in MSCs introduces unknown degradation phenomena that differ from those in ASCs. These phenomena include the degradation of the metal substrate and the interfacial reaction between the metal substrate and anode due to interdiffusion from the metal substrate and anode. Understanding and addressing the degradation phenomena originating from a metal substrate are significant challenges for the commercialization of MSCs. In this study, we investigated the degradation phenomena of MSCs, especially at the metal substrate/anode interface.The degradation phenomena are influenced by evaluation conditions such as durability time, temperature, and gas composition. The concentration of water vapor at the fuel gas outlet is much higher than at the fuel gas inlet throughout electrochemical reactions. To confirm the differences in the degradation phenomena due to gas composition, two MSC pieces were prepared. MSCs were fabricated at a lower temperature compared to ASCs, utilizing ceramic electrodes and electrolytes on a 16 cm2 ferritic stainless-steel substrate. Single cell tests were conducted using air at the cathode and fuel at the anode. The operating conditions for the evaluation were as follows: current density was varied from 0 to 0.42 A/cm², with H₂/H₂O used as the anode gas at two different dew points (DP). Test 1 was conducted at a DP of 30°C, and Test 2 was conducted at a DP of 88°C, while air served as the cathode gas. Both the anode gas and air flow rates were fixed during the evaluation. The operation was conducted with a fuel utilization factor (Uf) of approximately 10% and an air utilization factor (Ua) of approximately 20% at 0.42 A/cm².Figure 1 shows the results of the durability tests of 16 cm2-MSC cells conducted at 800°C. The change in voltage from the initial value is denoted as ΔV. The reduction in voltage on the fuel outlet side was approximately 25 mV greater than that on the fuel inlet side after 1000 hours. During these durability tests, the IR and electrode overvoltage (η) were measured by the current interruption method. The open circuit voltage remained stable without significant changes throughout the 1000 hours durability tests for both the fuel inlet and outlet sides. Figure 2 shows the results of IR and η during the durability tests conducted at 800°C. The observed reduction in voltage was attributed to increases in both IR and η, with similar increments noted for both the fuel inlet and outlet sides in relation to IR. It was found that no abnormally high resistance layer formation or significant increase in oxidation layer occurred on the outlet side after 1000 hours at 800°C.The more pronounced voltage drop observed at the outlet side is primarily due to a more significant increase in η. Considering that the evaluation was conducted under uniform conditions, except for the water vapor concentration on the anode gas side, it is plausible that the factors contributing to the increase in η are associated with the sintering or poisoning of the anode. These findings suggest that the reduction in reaction area and decreased gas diffusivity are significant contributors to the observed effects. In the presentation, we will discuss the insights derived from the electrochemical measurement results along with detailed cross-sectional analyses conducted after the durability tests. Figure 1

Direct internal reforming (DIR) operation provides many benefits for solid oxide fuel cells (SOFCs) by eliminating the need for an extra reformer. Anode-supported SOFCs (AS-SOFCs) are commonly used for DIR operations. However, the strong endothermic reforming reactions at the cell entrance may result in large thermal stresses and lead to premature failure. In this study, a two-dimensional model was developed to analyze the differences between the AS-SOFC and the new generation metal-supported SOFC (MS-SOFC) in DIR operations. The model considered the coupling effects of the chemical/electrochemical reactions, the mass/charge/heat transport processes and the thermal mechanical stress. The distributions of temperature, species composition, current density and thermal stress were determined and compared for both structures. The failure probability of the cell was estimated by stress distributions. The results showed that the MS-SOFC led to a gentler temperature distribution and a smaller failure probability with slight performance increase compared to the AS-SOFC.

Internal temperature prediction and control strategy design of anode-supported solid oxide fuel cell for hot start-up process

A novel route was developed to fabricate anode‐supported solid oxide fuel cells with a high throughput and low manufacturing costs. In contrast to classical manufacturing routes, this novel route starts with the tape casting of the thin electrolyte followed by the tape casting of the anode and anode support. All three layers were cast green‐on‐green and finally sintered to yield a gas‐tight electrolyte. By carefully selecting the raw materials for all three layers, it is possible to manufacture near‐net‐shape half‐cells. The half‐cells were characterized with respect to thickness, microstructure, bending behavior, electrolyte gas leakage, shrinkage, electrolyte residual stresses, and mechanical strength. Finally, the cathode was screen‐printed and fired, and the full cell characteristics were obtained in single‐cell and stack tests. Additionally, a scale‐up to cell sizes of 200 × 200 mm2 was verified. Electrolyte and anode thickness were around 20 μm, and the support was cast to 300–500 μm. The helium leak rates were better than the necessary internal threshold, and the characteristic bending strength obtained was in the range of 150–200 MPa. The single‐cell tests revealed current densities of 1.0 A cm–2 at 700 mV and 800 °C (H2/air). A first stack test proved their stackability and operational functionality.

Three-dimensional computational fluid dynamics modeling of anode-supported planar SOFC

A pressurized ammonia-fed planar anode-supported solid oxide fuel cell at 1–5 atm and 750–850°C and its loaded short stability test

The performance characteristics of high-performance Ni-YSZ (yttria-stabilized zirconia) anode-supported solid oxide fuel cells (SOFCs) are examined under typical fuel cell operating conditions over a period of ∼3000 h when hydrogen contaminated with different concentrations of H2S was used as the fuel. Analyses reveal some new insights into the sulfur poisoning behavior of a Ni-YSZ anode. First, an initial drop in power output upon exposure to H2S-contaminated fuels is more dramatic in an anode-supported cell (with small cell resistance) than in electrolyte-supported cell (with large cell resistance), creating an illusion that a high-performance cell appears to be less sulfur tolerant than a low-performance cell. Second, the transition time for this rapid performance drop to cease is much longer for an anode-supported cell (with a thicker anode) than an electrolyte-supported cell (with a thinner anode). Third, the degree of sulfur poisoning (or the cell resistance increase due to sulfur poisoning) diminishes with operating cell current density, suggesting that the water produced at the active sites on anode surface from electro-oxidation of hydrogen (or oxygen ions) may promote the oxidation and removal of adsorbed sulfur. This effect becomes less pronounced at higher concentration of H2S, but still significant at ∼1 ppm of H2S. Fourth, the subsequent slow degradation in performance after the rapid performance drop upon initial exposure to H2S can be avoided, indicating that the previously reported slow degradation is unlikely the inherent behavior of a Ni-YSZ anode, but associated with other complications. This further implies that sulfur poisoning may be reversible and the performance drop could be fully recovered when the fuel is switched back to clean hydrogen.

Solid oxide fuel cells for stationary, mobile, and military applications

An anode-supported solid oxide fuel cell (SOFC) was continuously operated with direct (anhydrous) ethanol for ~600 hours, with a high current density. The operation of the SOFC under ethanol was made possible with the deposition of a ceria-based catalytic layer onto the cermet anode support, which efficiently converts the primary fuel in hydrogen. The catalytic layer associated with the gradual internal reforming (GIR) process avoids carbon deposition on the Ni surface. The results provide a significant advance towards the development of direct ethanol solid oxide fuel cells.

The anode-supported solid oxide fuel cells (SOFCs) with an yttria-stabilized zirconia (YSZ) electrolyte have been successfully prepared by the sequential steps of fabricating technique including tape casting, spin coating, and screen-printing. Two types of the SOFCs are manufactured and their cell performances are characterized via the detail analysis of the electrochemical impedance spectroscopy (EIS). The maximum power densities are 411 and for the high and low performance cells at , respectively. According to the EIS analysis, the electrochemical performance of the poor cell is dominated by the anodic non-charge-transfer resistance, which is mainly resulted by the gas diffusion polarization due to the low porosity of the anode. The high performance cell is controlled by the simultaneous contributions of the ohmic resistance , the anodic polarization , and the cathodic polarization at the operation temperature of . However, the will dominate the performance of the cell as the temperature is lowered down to .

A simple, rapid spray method for preparing anode-supported solid oxide fuel cells with GDC electrolyte thin films