SOFC Cell Research Articles

High Altitude Airship Cabin Sizing, Pressurization and Air Conditioning

This paper aims at defining a design methodology for the global thermodynamic performance of a high altitude airship cabin. This design method applies to different systems, which could not use the traditional air conditioning plant layout based on bleed air intake from the compressor stage of jet engines. In the case of electrically propelled green vehicles and airships, other energy sources must be exploited. The MAAT EU FP7 project presents an innovative, energetically self sufficient, airship system based on cruiser-feeder architecture. Both the cruiser and feeder are fed by photovoltaic energy. The energy storage system by electrolysis and fuel cells with intermediate energy storage by hydrogen and oxygen is characterized by high temperature energy dispersions (about 800-1000°C for High temperature SOFC cells). This situation encourages the definition of a novel pressurization and air conditioning system. A preliminary cabin sizing with some structural considerations, an energetic evaluation of the thermal insulation of the cabin and a general balance of the energy production system are provided

원통형 고체산화물 연료전지 스택 제작 및 성능평가

In present work, optimized the manufacturing process of anode-supported tubular SOFCs cell and stack were studied. For this purpose, we first developed a high performance tubular SOFC cell, and then made electrical connection in series to get high voltage. The gas sealing was established by attaching single cells to alumina jig with ceramic bond. Through these process, we can obtain such high OVP as around 15V, which means that the electrical connection and gas sealing were optimized. Finally we developed a new tubular SOFC stack which shows a maximum power of 65W @ <TEX>$800^{\circ}C$</TEX>.

Effects of cathode materials on the characteristics of electrolyte supported micro-tubular solid oxide fuel cells

The effects of the GDC–LSCF (Ce0.8Gd0.2O0−δ–La0.6Sr0.4Co0.2Fe0.8O3−δ) cathode layer and the GDC interlayer on the electrochemical performance of the ScSZ (Zr0.8Sc0.2O2−δ) electrolyte supported (≈270 μm) micro-tubular SOFC cells are investigated in this study. Material formulation and sintering profile for fabricating the micro-tubular SOFC cells are developed to avoid physical defects caused by the large sintering shrinkage mismatch among the layers. Cell B (with the LSCF–GDC composite cathode layer and the GDC interlayer) reports an ohmic resistance slightly higher than that of Cell A (with the GDC–La0.8Sr0.2MnO3−δ, i.e. LSM, composite cathode), while its polarization resistance emerges to be significantly smaller than that of Cell A. In terms of cell performance, Cell B demonstrates an OCV value (>1.07 V) similar to that of Cell A and a maximum power density (0.26 W cm−2) 44.4% greater than that of Cell A (0.17 W cm−2) at 850 °C. It can thus be concluded that using the LSCF–GDC composite-cathode layer and inserting the GDC interlayer help reduce the total cell impedance, thereby improving the power density of the tubular cells.

Numerical analysis of optimal performance of planar electrode supported solid oxide fuel cell at various syngas flow rates

With the gradual scarcity of fossil fuels and the emergency demand of greenhouse gas emission reduction, coal, as the major energy source of China for a long time in the future, should be used efficiently and cleanly. The integrated gasification fuel cell (IGFC) hybrid power generation system is a promising clean coal utilization technology. In order to improve the performance of IGFC hybrid power generation system, the optimal performance of SOFC at different flow rate of syngas were numerically studied in this work. The performance curves of SOFC at various syngas flow rates were obtained. The results show that the temperature in the channel of SOFC cell is decreasing linearly with the increase of the syngas flow rate, when the average current density is constant. With the increase of syngas flow rate, the output voltage is reduced, but the optimal output power and the possible optional range of current density will increase. Under different mass flow rates, the fuel utilization at the optimal output power density decreases with increase of syngas flow rate. The polynomial function between the fuel utilization at optimal output power density and the mass flow rate of syngas was obtained.

Three-Dimensional Numerical Simulations of Heat and Mass Transfer and Degradation in a SOFC Cell Stack

We developed a three dimensional (3-D) mathematical model for a cell stack to perform comprehensive CFD analyses of degradation over a long period of time. The constructed 3-D CFD model consists of complete components in a practical SOFC stack. We calculated the concentration of the chemical species, the temperature distribution, the potential distribution, and the current density for each part of the stack. We also calculated the incremental electrical resistance using empirical formulas and predicted the change of electrical output and stack temperature distribution caused by degradation.

Redox-Stability of a Planar Metal-Supported SOFC

We report on the systematic examination of the redox behavior of a novel metal-supported SOFC cell type based on a porous Cr/Fe support and a thin YSZ-electrolyte layer applied by PVD methods. The oxidation of the Ni catalyst at the anode and the subsequent damage to the fuel cell microstructure is one of the main contributions to degradation of an SOFC. Our cell concept was tested for tolerance to cyclic oxidation and reduction of the anode, employing gravimetric and electron microscopy methods. The effects of redox cycling on the microstructure are examined and compared to corresponding results from state-of-the-art anode-supported SOFCs.

Application of Low Temperature Ceramic Coating Process for SOFC Electrolyte and Electrode Fabrication

Aerosol deposition, ceramic coating process by powder spray at room-temperature under low vacuum, is a promising process for preparation of SOFC cells and stacks’ component to minimize a detrimental reaction during cell production. Moreover, the process has flexibility of microstructure modification from gas-tight dense structure to porous structure with nano-scaled composites on various substrates including Ni-based cermet or even metal-support. In this study, we developed dense electrolyte coating of LSGM electrolyte on Ni-GDC, Ni, and Crofer22APU support, respectively, at room temperature, and achieved maximum power density of 1.31, 0.79, and 0.28 W/cm2 at 750oC, respectively. Nano-structured porous LSCF cathode were also prepared at room-temperature and polarization resistance of 0.11 Ω·cm2 was achieved.

Current SOFC R&D Activities at CNR-ITAE

The CNR-ITAE has a long and proven experience in SOFCs having contributed to the penetration of this technology into Europe since the early 1980's. In this communication will be reported the CNR-ITAE experience in the electrochemical screening of SOFC components under practical operating conditions, electrochemical process optimization on a small scale, and ex-situ physico-chemical characterization of the SOFC cells after operation.

Evolved Materials and Innovative Design for High Performance, Durable and Reliable SOFC Cell and Stack Presentation and Status of the European Project EVOLVE

Beyond the state of the art, EVOLVE aims at the development of a new cell architecture for SOFC, combining benefits of existing Anode Supported (high power density, lifetime) and Metal Supported cell (redox stability) architectures, while limiting the issue of sulphur poisoning by using enhanced perovskite anode materials. The core component is based on a composite anode substrate made of porous Alumina forming alloy combined with an electron conducting oxide ceramic, without having Nickel as structural component. A first Anode/Electrolyte assembly based on a NiCrAl foam and La0,1Sr0,9TiO3-α has been produced by means of Vacuum Plasma Spraying, showing the feasibility of this cell concept. With a requirement of a low temperature process, the manufacturing of the electrolyte layer remains the key challenge. Work is under progress for the manufacturing and testing of the first full prototype.

Effect of H2s On Ni-YSZ SOFC Anodes: A Combined In Situ Raman Spectroscopy-Impedance Spectroscopy Study

A combined Raman spectroscopy-impedance spectroscopy study of a Ni-YSZ anode of a SOFC cell has ben performed at 500°C in open circuit potential and at 500 mV polarization. The effect of adding 200 ppm H2S to the Ar-3 %H2-3% H2O feeding gas have been observed. In OCP conditions, the Raman spectrum of Ni3S2 is observed only 5.5 hours after the introduction of H2S, while the electrode impedance was reduced. The impedance grew only when the Raman signal of Ni3S2 saturated. At 500 mV polarization, Raman spectra of Ni3S2 were also observed together with a huge increase of the electrode impedance. For temperatures higher than 500°C, Ni3S2 shows no Raman spectrum, but high temperature optical spectroscopy shows that the growth of the Ni3S2 crystals can be observed at 715°C.

Research on the Relationship between SOFC Cell Performance, Adhesion Strength and Firing Temperature

SOFCs are expected to achieve high electrical conversion efficiency in the CHP systems with small generating power, but the improvement in durability performance is needed for commercialization. In order to improve durability, Toho gas is working on ways to prevent cathode from breaking away. In order to decrease abrasion, it is effective to rise the cathode’s firing temperature. However, the cell performance can decrease if the temperature is too high. This paper reports on the relationship between SOFC cell performance, adhesion strength, and calcination temperature in order to find the adequate firing temperature.

Mechanical Characteristics of Electrolytes Assessed with Resonant Ultrasound Spectroscopy

AbstractElastic properties and residual stresses are critical for the assessment of the reliability of ceramics components. The thin electrolyte layer of anode supported SOFCs is under a state of high compressive residual stress. In the present study, the elastic properties of this layer as well as the residual stress distribution induced in the anode‐supported planar SOFC cell were examined by using the resonant ultrasound spectroscopy (RUS). A modal analysis by finite element simulation demonstrated that the RUS has a great potential to determine these mechanical characteristics. The Young's modulus can be determined from the natural frequencies of the layered sample whilst the residual stress can be determined using the sample with a semi‐hole. Estimates of the Poisson's ratio are possible. In the experiment, various individual resonant oscillations were successfully identified using the present RUS system. Hence, by comparison of experimental results and simulations, the elastic properties as well as the residual stress were obtained. Although the proposed method is still experimentally challenging, it could be developed to become a powerful tool to simultaneously determine residual stresses and elastic constants of thin‐layered systems.

Reversible oxygen removal and uptake in the La2ZnMnO6 double perovskite: Performance in symmetrical SOFC cells

A polycrystalline oxygen-stoichiometric La2ZnMnO6 double-perovskite oxide has been prepared by soft-chemistry procedures, followed by annealing in air at 800 °C. A reduced specimen, with a La2ZnMnO6−δ composition, has been obtained by topotactical oxygen removal in an H2/N2 (5%/95%) flow at 600 °C. The structural characterization has been conducted from neutron powder diffraction (NPD) data, very sensitive to the contrast between Zn and Mn and the oxygen stoichiometry. Both perovskites (oxidized and reduced) crystallize in the monoclinic P21/n space group, exhibiting an antisite Zn/Mn disorder of about 15% and 14%, respectively. The partial reduction of Mn4+ to Mn3+ in the reduced phase is accompanied with the occurrence of oxygen vacancies, located at the axial octahedral sites. Thermogravimetric analysis (TGA) substantiates the oxygen stoichiometry and the stability range. Magnetic susceptibility measurements indicate an antiferromagnetic behaviour, confirming the presence of Mn3+ ions in the structure. The magnetic structure of the reduced phase, determined from NPD data at 3 K, shows an antiferromagnetic G-type coupling between Mn at 2c and 2d sites (promoted by the anti-site disorder); the ordered magnetic moment at Mn site is 0.789 μB at 3 K. Both phases display a semiconductor-like behaviour with a maximum conductivity of 0.052 S cm−1 for the reduced phase at 650 °C, due to the occurrence of Mn3+–Mn4+ mixed valence. Moreover, the measured thermal expansion coefficients perfectly match with the values usually displayed by SOFC electrolytes. The reversibility and versatility of the present compounds as catalysts for oxygen reduction (cathode) or fuel oxidation (anode) were tested in single SOFC cells yielding power density spanning from 120 to 155 W/cm2 using these perovskites as anode, cathode and symmetric electrodes for SOFC.

Electrochemical performance and thermal cyclicability of industrial-sized anode supported planar solid oxide fuel cells

Industrial-sized planar anode-supported SOFC cells with a cell dimension of 15 × 15 × 0.1 cm and an active area of 13 × 13 cm2 are fabricated through a processing route of tape casting-screen printing-cofiring. Electrochemical performance and thermal cyclicability of the cell are evaluated in a single cell stack at 750 °C with H2 as the fuel and air as the oxidant. With a gas flow rate of 3 L min−1, the initial open circuit voltage (OCV) is 1164 mV, and the stack demonstrates a power density of 380 mW cm−2 at 473 mA cm−2 with an extrapolated maximum power output of 100 W. After three thermal cycles, the reduction of the stack output voltage is around 5%, and the OCV is maintained at a level above 1145 mV. Based on the obtained results, issues related to stack performance, such as cell quality, contact resistance and sealing, are discussed.

Evaluation of Ln2CuO4 (Ln: La, Pr, Nd) oxides as cathode materials for IT-SOFCs

In this work an evaluation of Ln2CuO4 (Ln: La, Pr, Nd) cuprates is presented in terms of their possible application as cathode materials in Solid Oxide Fuel Cells working in an intermediate temperature range (600–800°C). The materials were synthesized by a soft chemistry EDTA-based method. Structural and microstructural characterization, measurements of transport properties and oxygen nonstoichiometry, determination of chemical stability in relation to Ce0.8Gd0.2O1.9 electrolyte, as well as mass relaxation studies for determination of oxygen diffusion coefficient D and surface exchange coefficient K in Pr2CuO4 and measurements of electrochemical properties of electrolyte-supported cells with Pr2CuO4 cathodes were performed. Pr2CuO4 and Nd2CuO4 oxides were found to possess tetragonal I4/mmm structure, in case of La2CuO4, orthorhombic Bmab one was observed. High temperature XRD data revealed anisotropic thermal expansion of Pr2CuO4, smaller along c-axis. Based on reduction experiments performed on TG apparatus, the initial slight oxygen excess δ present in the compounds at room temperature was evaluated: La2CuO4.03(2), Pr2CuO4.05(2) and Nd2CuO4.04(2). Additionally, it was observed that up to 900°C in air the oxygen content in the materials does not change considerably. Pr2CuO4 exhibits activated character of the electrical conductivity as a function of temperature, with values relatively high for cuprates, exceeding 100Scm−1 in 500–800°C range, as well as negative values of Seebeck coefficient from room temperature (RT) up to 800°C. Electrical conductivities of La2CuO4 and Nd2CuO4 are much lower in the temperature range of interest. Using mass relaxation technique it was possible to simultaneously evaluate D and K in 600–900°C temperature range. Activation energy of D was calculated to be 0.13(2)eV. Results of chemical stability studies in relation to Ce0.8Gd0.2O1.9 electrolyte revealed moderately good chemical compatibility of Pr2CuO4 oxide, while La2CuO4 and Nd2CuO4 stability proved to be insufficient. Using custom-made electrolyte-supported SOFC cells with Pr2CuO4-based cathode, it was possible to obtain power densities exceeding 0.1Wcm−2 at 800°C and 0.25Wcm−2 at 900°C.

Effects of changes in MOLB-type SOFC cell geometry on temperature distribution and heat transfer rate in interconnects

A numerical simulation tool for modeling MOLB-type solid oxide fuel cells was described. A mathematical model was developed and simulations were carried out to study the effect of cell geometry on the temperature distribution and heat transfer rate in interconnects. The simulations took into account the impact of co-flow and counter-flow patterns on the distribution of temperature. The results show that in counter-flow conditions there are lower temperature gradients and more uniform temperature distribution, which significantly affects conductive and corrosion properties and durability of the interconnect.

506 レーザ焼結法によるマイクロSOFCセルの作製(OS7-2 オーガナイズドセッション《精密/微細加工と評価》)

506 レーザ焼結法によるマイクロSOFCセルの作製(OS7-2 オーガナイズドセッション《精密/微細加工と評価》)

A Two-Dimensional Modeling Study of a Planar SOFC Using Actual Cell Testing Geometry and Operating Conditions

This paper reports a new electrochemical performance study performed on a planar SOFC cell. This study consists of a 2D model developed using a commercial software, namely Comsol Multiphysics. The model includes fluid dynamics, electrochemistry, electrical conduction, and diffusion physics. This model was built using the actual button cell testing geometry and using experimental data for validation purposes. The objective of this study is to understand the effects of the testing setup used on the cell performance and to recommend an improved design or geometry where the cell performance is independent of any flow maldistribution in both the air and fuel side of the SOFC cell. The air and fuel flow rates are studied to determine the effects on the cell performance. The effects of electrode porosities are studied together with the fuel and air flow rates. The distance from the SOFC cell to the discharge fuel feed tube and air chamber geometry are studied as well. The modeling results indicate that the SOFC electrochemical performance becomes independent of any flow maldistribution at relatively high flow rates for both fuel and air. Reduced electrode porosities play a role in the cell performance, and larger flow rates are required in order to achieve a cell performance independent of flow rates. The cell performance is also affected by the distance from the SOFC cell to the fuel discharge tube and the air chamber geometry. The behavior seen in the cell performance can be explained by a non-uniform mole fraction of reactants near the electrode surface.

Redox-cycling studies of anode-supported microtubular solid oxide fuel cells

Accidental reoxidation is one of the most critical issues of SOFC anodes, leading to performance degradation or even producing catastrophic failure of the cell. In this work several redox cycling experiments over microtubular SOFC cells are reported. Oxidation kinetic parameters have been determined for this geometry by Thermogravimetric Analysis (TGA). Oxidation kinetics is known to be diffusion limited at typical operation conditions and, for this reason, strictly dependant on geometry. A linear relationship was found between expansion kinetics and damage on SOFC anodes in a series of dilatometric experiments for the same temperature. A microtubular Ni-YSZ/YSZ/LSM-YSZ cell was also redox cycled several times at partial oxidation conditions (22% oxidation) and performance degradation was measured by j-V characterization and the loss was found to be approximately 2% in performance per cycle.

Analysis of the Use of a Porous Cathode in a SOFC Cell

not Available.