bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Impedance Studies on SOC
Authors: Vinke Izaak C. , Vibhu Vaibhav , Yildiz Saffet , Schiemann Kevin , Eichel Rüdiger- Albert , de Haart L. G. J.
Published: February 2020

In the institute for fundamental electrochemistry IEK-9 at the Forschungszentrum Jülich GmbH the electrochemical properties of solid oxide cells are electrochemically characterized at a variety of sizes, configurations and operating conditions. In various projects different aspects of the complete cell and the reversible oxygen electrode (ROE) are studies. Both electrode supported cells of 5 x 5 cm² and 20 mm diameter are characterized by galvanostatic DC methods and electrochemical impedance spectroscopy (EIS). Also electrolyte supported symmetric cells are studied using a configuration with reference electrodes to investigate the reversible air electrode in detail. The main focus lies on the use of EIS to try and understand the different fundamental (electrochemical) reactions within the electrode process.

Measurements are conducted on 5 x 5 cm² electrode supported cells comprising a 0.6 mm thick Ni/8YSZ fuel electrode, a 10 µm thick 8YSZ electrolyte, a 10 µm thick GDC diffusion barrier layer and a 50 µm thick LSFC air electrode. The impedance of the cells shows a continuous increase when progressing from fuel cell to electrolysis conditions (see Figure 1A). At high currents densities under both positive and negative current densities an inductive loop appears in the low frequency range. Due to the high currents involved and the use of a power booster during the measurements the EIS data are limited to ~10 kHz in the high frequency range. Therefore the EIS data do not directly show a high frequency intercept with the real axis and the Ohmic resistance has to be determined using a fitting procedure.

Similar measurements were also performed on 20 mm round or button cells of the same composition and microstructure. These cells show similar behavior (see Figure 1B). The overall shape of the impedance spectra is comparable for both cell types although the contributions of the underlying processes seem to vary with the cell size. Here the high frequency intercept can be determined but the measured data have to be corrected for an inductive contribution originating in the measurement setup.

To separate the contribution of the ROE from the total cell resistance, measurements on electrolyte supported cells with symmetrical CGO/LSCF electrodes and a platinum reference electrode are performed. Also here a continuous transformation of the EIS spectra can be observed when going from oxygen reduction in the fuel cell mode to oxygen evolution in the electrolysis mode.

By combining the data of all three different cell geometries an attempt is made to separate contributions from both electrodes and the influence of cell size on the total cell resistance.

Figure 1
Galvanostatic EFM: A New Approach for Testing and Monitoring Fuel Cells
Authors: Moosbauer Dominik Johann , Zhang Xueyuan , Yaffe Max
Published: February 2020

Electrochemical Frequency Modulation (EFM) is a well-known technique which is mostly used for corrosion studies. It is generally performed in potentiostatic mode and allows calculating the corrosion current as well as Tafel parameters by rearranging the Butler-Volmer equation. It was recently also used for testing fuel cells. However, for electrochemical power systems, galvanostatic control is much more beneficial. Even small potential changes can lead to high currents if a system has a very low internal resistance which can lead to irreversible damages at the cell and safety risks. Nonetheless, no practical and theoretical approach has been published so far for EFM measurement in galvanostatic mode.

This study presents first galvanostatic EFM measurements with fuel cells. The results are compared to other techniques which are typically used for analyzing fuel cells such as polarization experiments, electrochemical impedance spectroscopy (EIS), and current interrupt (CI). Measurements within this study are performed with a small Proton Exchange Membrane (PEM) fuel cell. During galvanostatic EFM experiments, a DC current signal is applied which is superimposed by a perturbation signal consisting of two sine waves with different frequencies (f
1, f
2). The measured voltage answer is more complex due to the non-linear behavior of fuel cells. The voltage signal can be subdivided into its DC response (zero frequency), harmonics (integral multiples of both base frequencies; f = n×f
1/2 where n is an integer > 0), as well as interharmonics (sum and difference of multiple harmonics; f = n×f
1 ± m×f
2 where n, m are integers > 0). In order to determine these terms, a fast Fourier transform (FFT) algorithm is employed on the measured signal. The voltage response can be plotted versus frequency in a so-called intermodulation spectrum. Harmonic and interharmonic amplitudes can be then used to calculate various parameters. As basis for all calculations serves the general equation for the cell voltage V
cellof a fuel cell:

V
cell = E
th - η
act - η
ohm - η
conc

The equation includes three major polarization terms that are responsible for voltage loss. These terms are the activation overpotential η
act, the ohmic overpotential η
ohm, and the concentration overpotential η
conc. E
th is the theoretical thermodynamic potential. The equation can be rearranged by expanding and substituting various terms. Similar to potentiostatic EFM, two causality factors can be extracted which can be used to proof validity of the measured results. Applicability of this method and its calculations are tested under various conditions such as different loads and oxygen concentrations. Finally, the results are compared with other techniques.
Evaluation of Performance and Heat Balance of Dry Reforming SOFC System
Authors: Kushi Takuto , Ohashi Masahumi , Kato Rei , Ito Takuya , Inagaki Shin , Amaha Shinji
Published: February 2020

SOFCs can achieve high electrical efficiency by utilizing steam reforming because the absorption reformate heat could be supplied from the heat from the stack and the anode off-gas combustor in the hotbox. However, water supply system leads to high manufacturing cost in BOP and may lead to decreased reliability of systems because of sensitive control. On the other hand, partial oxidation (POX) reforming system ensures the simplified system, while POX reforming system leads to lower electrical efficiency than in that of steam reforming because of fuel consumption in reforming.

From the background written above, we are focusing adapting full-scale CO2reforming (dry reforming) to SOFC systems to expand the capability of SOFCs. To reveal the feasibility of the dry reforming SOFC system, we have previously investigated the performance and durability of catalysts (reformer) and a cell stack in simulated dry reforming by comparing with that of steam reforming.

In this study, we investigated the performance of SOFC hotbox adapting dry reforming. The thermally self-supported state was successfully demonstrated in dry reforming operation. Additionally, this study discusses the heat balances of a hotbox under dry and steam reforming conditions. From the obtained results, we will introduce the problem and capability of the dry reforming SOFC system and discuss its feasibility.
Influence of Cell Design on the Performance of Direct Ammonia-Fueled Solid Oxide Fuel Cell: Anode- vs. Electrolyte-Supported Cell
Authors: Singh Vandana , Muroyama Hiroki , Matsui Toshiaki , Eguchi Koichi
Published: February 2020

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).
In-Cell Chromium Getters to Mitigate Cathode Poisoning in SOFC Stack
Authors: Uddin Md Aman , Aphale Ashish N , Hu Boxun , Pasaogullari Ugur , Singh Prabhakar
Published: February 2020

Incorporation of a porous and electrically conducting chromium getter layer consisting of a mixture of complex metal oxide getter and electrically conducting perovskite phases has been examined as a potential cost effective approach for the capture of gaseous chromium species originating from the metallic interconnect alloys conventionally used in SOFC stacks. Screen printed/ brush coated SrxNiyOz and conventional LSM/LSCF containing porous layer, deposited on the cathode surface, was electrically tested in a half cell configuration (3%H2O-Air/Pt//YSZ//LSM/Getter/3% H2O-Air-CrOx) at 850 °C for 100 hours. Cell current at 0.5 V bias was monitored and electrochemical impedance spectra (EIS) in frequency range of 0.5 Hz to 200 kHz were obtained at 1-hour interval with 10 mV sinusoidal amplitude. Post tested cells were analyzed for chromium concentration profile, reaction products chemistry and morphological changes. Our observations indicate that the gaseous chromium predominantly concentrates in the getter layer. The bulk electrode and electrode-electrolyte interface remain free of chromium. The electrical performance remains largely stable as evidenced by I-t and EIS data obtained during the test. Experimental details and results will be presented and discussed.
Microstructure and Electrochemical Properties of La0.8Sr0.2Ga0.8Mg0.2O3 Thin Film Deposited by Vacuum Cold Spray for Solid Oxide Fuel Cells
Authors: Wang Li-Shuang , Li Cheng-Xin , Ma Kai , Zhang Shan-Lin , Yang Guan-Jun , Li Chang-Jiu
Published: February 2020

Solid oxide fuel cells (SOFC) has attracted considerable attention in recent years as a power conversion system, owing to its high-energy conversion efficiency, fuel flexibility and low pollution emissions as well. Recently, the intermediate temperature-solid oxide fuel cell (IT-SOFC), which operates at lower temperatures (600~800 °C) to reduce cost and to improve efficiency, appears to be an alternative choice for the development of SOFC. La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM), with a perovskite structure, presents a high ionic conductivity at intermediate temperatures. However, the common methods to fabricate the LSGM electrolyte (e.g., solid state method) often lose their advantages owing to the depletion of Ga and the interfacial reaction between the LSGM and electrodes. Vacuum cold spray (VCS), based on the impact adhesion of fine particles to build up ceramic film at room temperature, is a new and promising method to fabricate thin (﹤20 mm) and dense (LSGM) electrolyte membrane. In the present study, the LSGM electrolyte layer with a thickness of ~10 mm is prepared by a home-developed VCS system assisted with in-situ particle heating approach (25~400 °C). The output performance of cells assembled with VCS-LSGM is determined at 500~750 °C. Results show that the OCV value is above 1.0 V, suggesting that the VCS-LSGM electrolyte is dense enough for the application to SOFC. Meanwhile, the ionic conductivities of LSGM coatings prepared by different in-situ particle heating temperatures were determined by an electrochemical impedance spectroscopy system. In addition, the microstructure and phase structure of LSGM coatings was characterized by scanning electron microscopy and X-ray diffraction. Based on this study, it is possible to conclude that the VCS is a promising method to prepare the LSGM electrolyte applied in the IT-SOFC.
Relationship between Electrochemical Properties and Electrolyte Partial Conductivities of Proton-Conducting Ceramic Fuel Cells
Authors: Matsuzaki Yoshio , Tachikawa Yuya , Somekawa Takaaki , Sato Koki , Kawabata Yasuharu , Sugahara Mariko , Matsumoto Hiroshige , Taniguchi Shunsuke , Sasaki Kazunari
Published: February 2020

Proton ceramic fuel cells (PCFCs) have attracted attentions because of the high potential to enhance the electrical efficiency of SOFCs, in which proton-conducting ceramic is used as electrolyte instead of the yttria-stabilized zirconia (YSZ) which is the most common electrolyte material of SOFCs.

In previous study, we measured the P
O2 dependence of total electrical conductivities of the proton-conducting solid oxides, BaZr0.1Ce0.7Y0.1X0.1O3-
d (X = Ga, Sc, In, Yb, Gd), which were divided into partial conductivities of the respective charge-carriers, such as electron, ion, and hole, by using the difference in P
O2dependence of the charge-carriers.

In this study, we have investigated the electrochemical properties of the PCFCs with the various partial conductivities in the electrolytes. The electrochemical properties were found to have large dependences on operation condition. When ASR and external current density were given constant values of 0.383 ohm cm2 and 0.25 A cm-2, respectively, an influence of the dopant species on the electrical efficiencies η
xwas found to have the following sequential order:

η
x=SC > η
x=In > η
x=Ga > η
x=Y > η
x=Gd

When the external current density was given as a variable, increasing the external current density will result in the increase of the voltage drop and the decrease of a ratio of leakage current to external current. This suggests that according to the partial conductivities the external current density has an optimum value maximizing the electrical efficiency.

Acknowledgements

This research is supported by The Japan Science and Technology Agency (JST) through its “Center of Innovation Science and Technology based Radical Innovation and Entrepreneurship Program (COI Program)."
Three-Dimensional Modelling of a Microtubular SOFC: A Multiphysics Approach
Authors: Hodjati-Pugh Oujen , Dhir Aman , Steinberger-Wilckens Robert
Published: February 2020

There is an increasing interest in the use of Microtubular Solid Oxide Fuel Cells (µ-SOFC) for a broad spectrum of applications with power demands ranging from a few watts to several hundred watts. µ-SOFC’s possess inherently favourable characteristics over alternate configurations such as high thermo-mechanical stability, high volumetric power density and rapid start-up times. The use of computational modelling at the design level is essential for minimising cost and maximising productivity, giving critical insight into the complex phenomena occurring during SOFC operation and their interrelationships.

To date, models have been limited by oversimplified geometries, often failing to account for cathode air supply complexities, gas distribution within pores and radiative heating effects[1-3]. In this study, a three-dimensional Computational Fluid Dynamics (CFD) model of an anode, electrolyte, cathode, current collectors, fuel inlet/outlet and furnace temperature effects is considered. The model has been validated with a mirroring experimental setup, varying fuel compositions, operating temperature and interconnect configuration. COMSOL Multiphysics is used to simulate the physics, describing the distribution of temperature, current density, electrical potential, pressure and gas concentrations throughout the cell. Results show good correlation with experimental data and the model is reliable for prediction of fuel cell performance as a function of operating conditions within these set parameters.

References

[1] D. Cui, B.Tu, M.Cheng, Journal of Power Sources, 297 (2015) 419-426

[2] M.Lockett, M.J.H. Simmons, K.Kendall, 8th Grove Fuel Cell Symposium, Elsevier Science Bv London, (2003)

[3] D.Cui, L.Liu, M.Cheng, Journal of Power Sources, 174 (2007) 246-254
Evolutionary Programming Based Approach for SOFC Cathode Characterization: A Case Study on Co-Free Mixed Conducting Perovskites
Authors: Oz Alon , Gelman Danny , Tsur Yoed , Singh Kalpana , Thangadurai Venkataraman
Published: February 2020

Electrochemical impedance spectroscopy (EIS) is a powerful technique to characterize the performance of solid oxide fuel cells (SOFCs). Given a proper analysis technique, EIS data can shed light on the different contributions to the total impedance. The most common analysis technique is equivalent circuit modelling (ECM), where a combination of resistors, capacitors, constant phase elements, etc. represents the physical response of the sample. ECM has its known drawbacks, e.g. non-uniqueness and obscure physical meaning of the chosen model. Using impedance spectroscopy genetic programming (ISGP), based on evolutionary programming, those challenges are better tackled. Our analysis focuses on finding the distribution function of relaxation times (DFRT). The analysis procedure using ISGP yields a DFRT model comprised of known mathematical peaks. Each peak in the model is characterized by its height, width and relaxation time. It is possible to assign each peak to one or more process, and to calculate its area. Thus, we are able to determine the contribution of each process to the total impedance. By plotting the DFRT as a function of frequency it is possible to identify the different polarization processes and gain additional information, which may be convoluted and therefore undetected in other analysis techniques.

Here, we report the electrochemical performance of perovskite-type Co-free cathodes such as Ba0.5Sr0.5Fe0.91Al0.09O3-δ, Ba0.5Sr0.5Fe0.8Cu0.2O3-δ, and Ba0.5Sr0.5Fe0.8Nb0.2O3-δ with oxide ion conducting La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) and proton conducting Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-δ electrolytes have been investigated by ISGP. Composites of cathode with electrolytes were screen printed on both sides of electrolyte in order to get symmetrical cells for evaluating cathode performances. EIS of symmetrical cells at different experimental conditions were analyzed by ISGP. Thus, by changing parameters and monitoring corresponding changes in the peaks’ relaxation times and areas, in-depth understanding of the operation of various components of the symmetrical cells such as the oxygen reduction reactions, mass transfer limitations and the electrolyte ionic conductivity can be achieved.
Oxygen Reduction Reaction Properties of Cobalt-Free Perovskites for SOFCs
Authors: Singh Kalpana , Sahoo Akankshya , Thangadurai Venkataraman
Published: February 2020

Doping is one of the pathways through which electronic and ionic conductivity can be tuned in metal oxides. In this study, the oxygen reduction reaction (ORR) properties of Ba0.5Sr0.5Fe0.91Al0.09O3-δ (BSFAl), Ba0.5Sr0.5Fe0.8Cu0.2O3-δ (BSFCu) and Ba0.5Sr0.5Fe0.8Nb0.2O3–δ (BSFNb) are investigated using proton conducting (Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-δ, BSCZGY) and oxide ion conducting (La0.8Sr0.2Ga0.8Mg0.2O3-δ, LSGM) electrolytes. BSFAl and BSFCu were synthesised through combustion method, whereas BSFNb was synthesised through solid-state method. BSFCu-LSGM/LSGM/BSFCu-LSGM symmetrical cell showed lower area specific resistance (ASR) of 0.077 Ω cm2 in air at 850 °C than BSFAl-LSGM/LSGM/BSFAl-LSGM cell. In air medium, symmetrical cells with LSGM exhibited lower ASR values than BSCZGY symmetrical cells owing to its higher ionic conductivity. In order to understand more about the oxygen consumption and release properties in these oxides, thermogravimetric analysis in varying pO2 were performed. In all pO2, BSFAl showed the highest weight loss and gain during heating and cooling cycles, while BSFNb showed the lowest weight gain and loss. Detailed discussion on oxygen nonstoichiomtery and ORR of Co-free perovskite-type oxides will be presented in this talk.
Methane Pulse Study on Nickel Impregnated Gadolinium Doped Ceria
Authors: Ouyang Mengzheng , Boldrin Paul , Brandon Nigel P.
Published: February 2020

Nickel/gadolinium doped ceria (Ni/CGO) has been a popular SOFC anode material for decades for its superior mix conductivity and excellent oxygen storage capacity. However, the study of Ni/CGO in a realistic working condition is still lacking. Also, not much research has linked the chemical properties of CGO with the carbon resistance which is essential when using hydrocarbon as fuels.

In this research, Ni/CGO powder was prepared via impregnation-calcination method. A novel pulse experiment has been conducted on impregnated powder. We did certain pulses of a fixed amount of methane into the sample at 600℃.The outlet gas composition was monitored by a quadrupole mass spectrometer.

The product gas was composed of several species including hydrogen, steam, carbon monoxide, carbon dioxide, and methane that was not participated to the reaction.

The major reaction was the partial oxidation of methane that produced carbon monoxide and hydrogen. With the increase of pulsing numbers, the product and shape of product peaks changed a lot. Also, we observed a “tail” after each carbon monoxide production peak which extend with the number of pulsing. This was deduced to be caused by the self-oxidation of carbon by the bulk migrated oxygen. These changes revealed the changing of CGO during methane oxidation.

After detailed quantitative analysis of the shape and integrated intensity of the peaks and tails. We confirmed that the majority of methane partial oxidation reaction on Ni/CGO follows a deposition-oxidation route rather than direct oxidation of methane. Also we were able to evaluate the ability of carbon self-oxidation with different ceria oxidation state. Consequently, a model was proposed to elucidate the relation between carbon self-oxidation rate, surface oxygen concentration and bulk oxygen migration rate of CGO, in forms of partial differential equation.

In-situ Raman spectroscopy was performed during the pulse experiment to give a direct parallel evidence. We observed the change of CGO surface oxygen stoichiometry and deposited carbon. Thus we can confirm the conclusion deduced by pulse experiments to prove its validation, and directly relate the carbon self-oxidation rate with bulk oxygen migration rate of CGO.

The results provided a novel yet facile method to evaluate the oxygen storage properties of materials and gave an insight into the design and modification of ceria based SOFC anode materials.
Dependence of Syngas Composition on Microstructure of La0.8Sr0.2Cr0.5Mn0.5O3–δ Based Cathode for CO2 and H2O Co-Electrolysis
Authors: Maide Martin , Lillmaa Kadi , Nurk Gunnar , Lust Enn
Published: February 2020

Ceramic materials with perovskite structure have attracted attention as possible redox stable, sulfur- and carbon tolerant cathode materials for solid oxide electrolysis cells 1,2. For example, composite cathode based on La0.8Sr0.2Cr0.5Mn0.5O3-δ (LSCM) are used for high temperature electrolysis of steam and co-electrolysis of steam and carbon dioxide 3,4. However, the limitation of electrochemical performance of electrolysis cell due to insufficient electrocatalytic activity can be a serious challenge 5.

In this study, catalytically active nickel and copper nanoparticles were grown on the surface of A-site deficient LSCM via redox exsolution. Influence of water-gas shift reaction activity conditions of electrolysis and nanocatalyst properties on the outlet gas composition were evaluated.

Electrolysis cells were prepared by sandwiching dense Zr0.89Sc0.10Ce0.01O2-δ (ScCeSZ) electrolyte layer between porous ScCeSZ layers and followed by wet impregnating of electrocatalytically active electrodes into the porous matrix. Impregnated salt mixture is decomposed at 400 °C, calcined and then sintered at 1400°C for 5 h. The thicknesses of the dense electrolyte and the porous scaffold were approximately 100 μm and 40 μm, respectively. Scanning electron microscopy, X-ray diffraction, FIB-TOF-SIMS and ICP-MS methods were used to characterize materials. Electrochemical characterization and analysis of outlet gas composition using gas chromatography was carried out at temperature range from 650 to 850 °C in various H2O, CO2, H2 and Ar inlet concentrations.

As expected, the activity of composite cathode was greatly enhanced by the exsolved nickel and copper nanoparticles. For gas compositions the influence of water-gas shift (WGS) for nickel was greater than for copper.

Thus, it has been demonstrated that both nickel and copper nanoparticles can enhance the electrolytic activity of the cathode for steam electrolysis and co-electrolysis of steam and carbon dioxide. Influence of water-gas shift reaction at co-electrolysis conditions and properties of nanocatalysts on the outlet gas composition were evaluated.

References:

1. O. A. Marina, L.R. Pederson, M.C. Williams, G.W. Coffey K.D. Meinhardt, C.D. Nguyen and E.C. Thomson, J. Electrochem. Soc., 154, B452 (2007).

2. S.-E. Yoon, J.-Y. Ahn, B.-K. Kim, and J.-S. Park, Int. J. Hydrogen Energy, 40, 13558 (2015).

3. X. Yang,J. T. S. Irvine, J. Materials Chemistry, 18, 2349-2354 (2008).

4. R. Xing, Y. Wang, S. Liu, J. Power Sources, 208, 276-281 (2012).

5. X. Yue, J. T. S. Irvine, Solid State Ionics, 225, 131-135 (2012).
Numerical Simulation of LSCF-GDC Composite Cathodes with Various Microstructures
Authors: He An , Kim Yongtae , Shikazono Naoki
Published: February 2020

In the present study, the electrochemical performances of different LSCF-GDC microstructures are numerically calculated in order to investigate the effects of GDC particles and GDC pillars on LSCF cathode microstructures with various particle sizes. Lattice Boltzmann method (LBM) is applied for solving the governing equations. It is found from the numerical results of pure GDC and LSCF-GDC composite cathodes with various particle sizes that GDC addition improves LSCF cathode electrochemical performance. This performance improvement is more pronounced for cathodes with smaller particle sizes and when operated at lower temperatures. In addition, it is shown that LSCF cathode with GDC pillars can enhance the performance of the cathode. The GDC pillars are even more effective when the reactive region of the cathode becomes thin by using small size powders.
Investigation of La0.6Sr0.4Co0.2Fe0.8O3-
δ Electrode Performance and Microstructural Evolutions Based on Three Dimensional Microstructure Reconstruction and Electrochemical Simulation
Authors: Shimura Takaaki , He An , Kim Yongtae , Jiao Zhenjun , Shikazono Naoki
Published: February 2020

The influence of initial microstructure of gadolinium-doped-ceria (GDC) interlayer on La0.6Sr0.4Co0.2Fe0.8O3-
d (LSCF) performance was studied with three dimensional microstructure reconstruction by focused ion beam – scanning electron microscopy (FIB-SEM). When the GDC interlayer was fired at 1300 ˚C (GDC1300), discontinuous SrZrO3 phase was formed between GDC interlayer and yttria-stabilized-zirconia (YSZ) electrolyte. In addition, inter-diffused layer of GDC and YSZ was formed at the neighbor of the SrZrO3 phase and along the YSZ electrolyte interface. When the GDC interlayer was fired at 1200 ˚C (GDC1200), continuous SrZrO3 layer was formed. Inter-diffused layer was formed along the YSZ electrolyte. Both cells were operated at 700 ˚C and 800 ˚C . The initial electrode resistance of GDC1200 was more than 20 times larger than that of GDC1300. Slight increase of electrode resistance was found for GDC1300 after the cell operation, whereas the drastic activation was found for GDC1200. The activation was enhanced at operating temperature of 700 ˚C than 800 ˚C . For GDC1300, Sr rich phase was formed after the operation at 800 ˚C. It is considered that the differences of performance and microstructural evolution are highly dependent on initial microstructures and operating temperatures. The different electrode performances are evaluated based on electrochemical simulation using reconstructed microstructures.
Materials Properties for the Simulation of Electro-Chemo-Mechanical Coupling Behavior of SOFC
Authors: Yashiro Keiji , Kawada Tatsuya , Watanabe Satoshi , Muramatsu Mayu , Sakamoto Tadashi , Hashimoto Shin-ichi , Terada Kenjiro , Sato Masami , Hashida Toshiyuki , Sato Kazuhisa , Iguchi Fumitada , Yugami Hiroo , Amezawa Koji , Nakamura Takashi , Kimura Yuta , Unemoto Atsushi
Published: February 2020

Research and development of solid oxide fuel cells (SOFCs) have been mainly conducted from the aspect of electrochemistry and materials science to improve cell- and stack performances. Long-term reliability and durability are of great importance for the commercialization of SOFCs. Mechanical behaviors of ceramics components, including cell fracture, are necessary to be understood in order to ensure stability of SOFCs. For the multiscale simulation of the thermo-chemo-mechanical behavior, various related materials properties are indispensable. This paper reports the evaluation procedure for comprehensive analysis of chemically- and thermally induced mechanical behavior of SOFCs.
A-Site Deficient La2-XNiO4+δ Infiltrated LSCF Cathode with Improved Performance and Stability
Authors: Zhang Xinxin , Li Wenyuan , Guan Bo , Liu Xingbo
Published: February 2020

In this study, to avoid the surface segregation of La2O3 and LaNiO3 phases on the lanthanum nickelate (La2NiO4+δ) infiltrated LSCF cathode, A-site deficient lanthanum nickelate (La2-xNiO4±δ) are investigated as the infiltrant. La2-xNiO4±δ (x=0-0.2) are synthesized and characterized first. The maximum deficient concentration of lanthanum is less than 0.2. La2-xNiO4±δ with higher deficient exhibits the enhanced electrical conductivity below 800oC. Through the electrochemical impedance spectroscopy on the symmetrical cells, it is found that A-site deficiency lead to an increase in the polarization resistance. The surface charge transfer process gradually dominates the impedance with lanthanum deficiency increasing. In the infiltrated LSCF cathode, it is observed that about one order of magnitude decrease in polarization resistance has been achieved after La2-xNiO4±δ ­infiltration, with La2-xNiO4±δ)-infiltration being the smallest. In a short-term measurement, after 960 min cathodic polarization at -0.2V, the degradation of La2-xNiO4+δ (x=0-0.2) coated LSCF reduces with increasing A-site deficient concentration. The enhanced stability of La2-xNiO4+δ (x=0-0.2) coated LSCF demonstrates that A-site deficient La2-xNiO4+δ is one potential infiltration materials for LSCF cathode to improve the surface stability.
Metal Supported SOFCs: Electrochemical Performance under Various Testing Conditions
Authors: Haydn Markus , Bischof Cornelia , Udomsilp David , Opitz Alexander Karl , Bimashofer Gesara , Schafbauer Wolfgang , Brandner Marco , Bram Martin
Published: February 2020

Since many years solid oxide fuel cells (SOFCs) are used in stationary systems, in a range from 0.1 up to 1,000 kW, to generate electric power or combined heat and power (CHP). For these applications, electrolyte or anode supported cells (ESCs, ASCs) are the preferred SOFCs and have been demonstrated in different installation environments. In the last years lots of research has been done on metal supported solid oxide fuel cells (MSCs) for mobile applications e.g. auxiliary power units (APUs) or range extenders. For this type of cell, a powder-metallurgically manufactured metal substrate (e.g. Fe26Cr) works as backbone of the cell. This substrate is highly porous and its coefficient of thermal expansion (CTE) matches quite well with the commonly used 8YSZ (8 mol% Y2O3 fully stabilized ZrO2) ceramic electrolyte material. This adopted CTE avoids cracks within the electrolyte layer during heating-up and cooling-down procedures as well as the operation itself. Besides, the ductile substrate together with the thin electrolyte is very robust against vibrations. The anode is applied onto the metal substrate via screen printing and sintering and consists of porous Ni/8YSZ, which is a very well-known SOFC anode material. The anode reduces the pore size of the coarse porous metal substrate by more than one order of magnitude and enables the thin electrolyte to gas-tightly separate the porous anode from the cathodic side. The electrolyte (8YSZ) is rather thin being applied by a special PVD-process, a gas flow sputtering process. Compared to ESCs or ASCs, this thinness enables lower operation temperatures, which is advantageous for mobile applications. Lastly, the cathode is applied via screen printing and consists of porous LSCF (La0.6Sr0.4Co0.8Fe0.2O3-δ), which is also well-known in the SOFC community.

To show the performances and reliabilities of MSCs, a series of electrochemical characterizations on button cells were performed. The cell conditioning during heat-up will be described as it is slightly different to that of ASCs and ESCs. The main focus of this proceeding is to show the influence of gas-flow rates, gas compositions and operational temperatures on recorded i-V-curves. To do so, some of the testing parameters work at high fuel utilization rates, which is not commonly used for button cell experiments. However, with this parameters, it was interesting to see, how the anode and the metal substrate handle high humidity. Furthermore, significant performance improvements with recently developed anodes and cathodes will be presented.

To sum up, this conference proceeding gives an overview on (i) manufacturing, (ii) appropriate test procedures, and (iii) electrochemical testing of MSCs.
Methane-Fueled Proton-Conducting Ceramic Fuel Cell Stacks
Authors: Ding Hanping , Le Long Quoc , Sullivan Neal P
Published: February 2020

We present our recent work on scale-up and stack development of fuel cells based on proton-conducting ceramic materials. Through steady improvement in materials and fabrication methods, protonic ceramics are emerging from the laboratory as potential solutions in electricity generation, energy storage, and chemical synthesis. “Button-scale” protonic ceramic fuel cells (PCFCs) based on barium zirconates have demonstrated high power density at low operating temperatures, reaching 450 mW / cm2 at 500 ºC under hydrogen fuel, and 300 mW / cm2 at 550 ºC under direct methane-steam fuel. While these materials show great promise, scale up of protonic-ceramic fuel cells beyond the “button-cell” level remains limited.

In this presentation, we review our progress in extending previous button-cell experiments to small fuel-cell stacks. First, fabrication procedures have been developed to increase PCFC active area by a factor of 10. These planar, circular membrane electrode assemblies (MEAs) are packaged within the stack architecture shown in the figure. MEAs are bonded within a ceramic frame, and the frame is packaged within ferritic-steel interconnects. Numerous multi-cell stack prototypes have been demonstrated. A three-cell stack based on BaCe0.2Zr0.6Y0.2O3-d (BCZY26) electrolyte shows near-theoretical open-circuit voltage and promising power density under methane fuel (183 mW / cm2 at 500 ºC). In this presentation, we will review our continuing efforts to improve the performance and durability of protonic-ceramic fuel cell stacks.

Figure 1
Effects of Non-Proton-Conducting Anode Supports on the Performance of Thin-Film Protonic Ceramic Fuel Cells
Authors: Bae Kiho , Kim Dong Hwan , Jang Dong Young , Choi Hyung Jong , Son Ji-Won , Shim Joon Hyung
Published: February 2020

Protonic ceramic fuel cells (PCFCs) have been proposed as a ceramic fuel cell effectively operating at intermediate temperature range (IT) of 500‒700 °C (1‒5). Key to developing high performance PCFCs is the incorporation of thin protonic ceramic (PC) electrolytes as ohmic resistance by ion transport across the electrolyte membrane accounts for a significant portion of the energy loss during fuel cell operation. In order to stably accommodate the thin-film electrolyte, it is important to prepare a good anode support. Composite wafers composed of NiO and electrolyte ceramics are most commonly used as anode supports (3‒5). For example, PCFCs with yttrium-doped barium zirconate (BZY) electrolytes typically use the NiO-BZY compound as anode support. However, it is difficult to prepare NiO-PC composites because of the different sintering temperatures between NiO (~1200 °C) and PC (~1700 °C for BZY). These discrepancies tend to result in excessive growth of NiO and unevenly distributed pores, which labilize the overall stacks during fuel cell operation.

To solve this problem, we have recently proposed to use NiO-yttrium doped zirconia (YSZ) as the anode support (5). This material is the most common anode support for solid oxide fuel cells that have been proven to work effectively. This approach requires to tightly integrate the PC electrolyte onto the NiO-YSZ surface and to minimize thermal stresses at the interface. To this end, a thin NiO-PC interlayer was prepared before depositing the PC electrolyte. As a PC material, yttrium-doped barium zirconate cerate (BZCY) was used. As a result, PCFCs with Ni-YSZ anode supports tightly accommodating thin-film BZCY electrolytes have successfully demonstrated open circuit voltages (OCV) over 1 V and power outputs of 740 mW/cm2at 650 °C (5). In this presentation, we will discuss this achievement in more details and recent progresses on this topic.

1. J. H. Shim, J. S. Park, J. An, T. M. Gur, S. Kang, and F. B. Prinz, Chem. Mater., 21, (2009) 3290-3296.

2. K. Bae, D. Y. Jang, H. J. Jung, J. W. Kim, J. W. Son, and J. H. Shim, J. Power Sources, 248, (2014) 1163-1169.

3. C. Duan, J. Tong, M. Shang, S. Nikodemski, M. Sanders, S. Ricote, A. Almansoori, and R. O’Hayre, Science, 349, (2015) 1321-1326.

4. K. Bae, S. Lee, D. Y. Jang, H. J. Kim, H. Lee, D. Shin, J.-W. Son, and J. H. Shim, ACS Appl. Mater. Interfaces, 8, (2016) 9097-9103.

5. K. Bae, H.-S. Noh, D. Y. Jang, J. Hong, H. Kim, K. J. Yoon, J.-H. Lee, B.-K. Kim, J. H. Shim, and J.-W. Son, J. Mater. Chem. A, 4, (2016) 6395-6403.
Anode Fluidization of a Liquid Tin Anode SOFC Operated on Simulated Syngas
Authors: Cao Tianyu , Shi Yixiang , Cai Ningsheng
Published: February 2020

Liquid tin has been widely employed as anodes in SOFCs to digest carbonaceous fuels. Liquid tin anode SOFCs fed on methane, kerosene, and carbon black have been successfully constructed and operated. However, the formation of a SnO2 blocking film at electrochemical reactive sites hinders further electrochemical reaction and impedes steady power generation of the fuel cell system. Here we manage to suppress the formation of isolating SnO2 film by anode fluidization. Tubular liquid tin anode SOFC has been fabricated and tested in present work. Fuels (H2 and simulated syngas with different H2/CO ratio) are supplied to the electrochemical reactive interface between the anode and the electrolyte via a manner of bubbling bed. H2 was found to effectively reduce SnO2 formed when the SOFC was discharged at a constant potential of 0.45V, and anode fluidization has doubled the fuel cell’s power output. We anticipate that anode fluidization in this study will principally simplify the configuration of liquid tin anode SOFC and maintain the stable operation of the fuel cell system.

Figure 1
Study on the ORR Mechanism and CO2-Poisoning Resistance of La0.8Sr0.2MnO3-δ-coated Ba0.5Sr0.5Co0.8Fe0.2O3-δ Cathode for Intermediate Temperature Solid Oxide Fuel Cells
Authors: Qiu Peng , Yang Jiajun , Jia Lichao , Gong Yingpeng , Pu Jian , Li Jian
Published: February 2020

The LSM-coated BSCF cathode with 3D core-shell architecture had been fabricated by the solution impregnation technology and presented the excellent CO2-poisoning resistance at the operating temperature. The LSM shell limited the combination of CO2 and BSCF, making that the 3D core-shell cathode present the great CO2-poisoning resistance. The three-electrode measurement was carried out to investigate the ORR mechanism. As the intervention of LSM shell, the LSM-coated BSCF presented the different ORR rate-determining step comparing with the BSCF cathode. The formation of lattice oxygen was the rate-determining step for the LSM-coated BSCF cathode, while molecular oxygen surface adsorption for the BSCF cathode. In addition, the electrochemical stability was promoted greatly with the protection of LSM shell. The LSM-coated BSCF cathode could get the stable state at about 11 h under cathodic current passage of 400 mAcm-2 at 650 °C, while it was about 70 h for the BSCF cathode. The excellent electrochemical performance and CO2-poisoning resistance made that the LSM-coated BSCF cathode appears to be a promising cathode for IT-SOFCs.
Investigation of Cr Poisoning on the LSCF Cathode Under Different Temperatures for Solid Oxide Fuel Cell
Authors: Xiong Chunyan
Published: February 2020

The Cr poisoning effect on cathode is identified as a considerable negative factor for the long-term performance of Solid Oxide Fuel Cells(SOFCs). With the lowering of the operating temperature of SOFCs, more high performance cathode materials could be used. In this study, the relation between testing temperature of SOFC and the Cr poisoning effect on La0.6Sr0.4Fe0.8Co0.2O3-δ - Ce0.9Gd0.1O2-δ symmetric cells is investigated . Combined with the SEM and XRD , a secondary phase, identified as SrCrO4 is found formed on the surface of cathode to cause serious cathode degradation. The EIS shows that as the increasing of performance temperature from 550°C to 750°C, the Cr poisoning effect firstly increases to the maximal poisoning effect on 650°C and then decreases as the increasing of testing temperature. The evaporation of Cr from metallic interconnect could increase with the rising of testing temperature, However , the surface incorporation and exchange of Cr or O2 may not obey the tendency of temperature. With the DRT calculation, the Cr is more easily to occupy the Co sites on the LSCF but O is more tend to occupy the Sr sites, which may lead to the existence of the peak performance temperature for the remarkable Cr poisoning effect on LSCF.
Modification of Ni-YSZ Surface with High Carbon Tolerance Using GDC Nanoparticles
Authors: Wang Fangfang , Kishimoto Haruo , Ishiyama Tomohiro , Bagarinao Katherine Develos- , Yamaji Katsuhiko , Horita Teruhisa , Yokokawa Harumi
Published: February 2020

In order to find a good approach to suppress the carbon deposition on Ni surface for Ni/YSZ anode of solid oxide fuel cells, in this work, the Ni surface was modified by GDC nanoparticles with tens of nanometer by using pulse laser deposition technique. The carbon deposition experiment was carried out for the samples with exposing to dry 5% CH4-Ar mixture at 800 oC for 3 h. The severe carbon deposition behavior is observed on Ni film for Ni/YSZ. On the other hand, the suppression of carbon deposition behavior appeared for Ni/YSZ modified by GDC nanoparticles. The high catalytic activity of this modified Ni/YSZ is confirmed in humid methane by investigating the methane and hydrogen conversion. It suggests that the modification of Ni surface using GDC nanoparticles is a good approach to suppress the carbon deposition behavior for Ni/YSZ when methane is used directly as the fuel gas.
Economic Analysis and Implementation Strategies for SOFC Systems in Residential Applications
Authors: Zhao Li , Brouwer Jack
Published: February 2020

In this study, we installed and evaluated a 1.5 kW Solid Oxide Fuel Cell (SOFC) with Micro-CHP (combined heat and power) system as a Distributed Generation (DG) prime mover in a residential application. Both steady state and dynamic operating conditions were evaluated. With the steady state and dynamic performance characteristics of the SOFC CHP system, and the latest capital cost and performance data garnered from the ENE FARM Program (Japan) and ene. field Program (Europe), we carried out an economic analysis taking into account the daily and seasonal energy production, residential utility rates, fiscal incentives by state, and effective photovoltaic (PV) capacity integration. Various operation strategies that focus on 1) reduced energy use, 2) reduced peak demand, 3) PV integration at the residence, and 4) qualifications for fiscal incentive programs are evaluated. From the customer perspective, this study generates a guideline for the user to make decisions regarding SOFC system capacity, operating strategy and CHP configuration, while providing guidance regarding the breakeven costs of SOFC systems under various scenarios in various regions.
Exploring Alternative Polymer Compositions for Highly Conductive Solid Polymer Composite Electrolytes
Authors: Shen Brian H , Tenhaeff Wyatt
Published: February 2020

Battery safety is increasingly at the forefront of consumer concerns, especially regarding electric vehicles. Current lithium ion battery technology utilizes liquid electrolytes, which have very high ionic conductivities but are extremely flammable. To improve safety, researchers are investigating replacing liquid electrolytes in lithium ion batteries with solid electrolytes. A promising approach is the use of solid polymer composite electrolytes where lithium conductive ceramic powders are dispersed into polymer electrolyte matrix. These materials are intended to improve lithium conductivities and mechanical properties relative to pure polymer electrolyte, lower manufacturing and battery cell construction costs relative to using pure ceramic electrolytes, and eliminate volatile and flammable electrolyte solvents. Currently, the archetypal polymer matrix used in composite electrolytes is polyethylene oxide (PEO). When mixed with lithium salts, such as lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and ceramics, such as Li7La3Zr2O12 (LLZO), PEO based composites have conductivities (~10-7 S/cm at room temperature) that are still insufficient for today’s applications. In addition, PEO tends to crystallize and has poor oxidative stability (decomposition ca. 4V). We are exploring poly(polyethylene glycol methyl ether methacrylate) (PEGMA) and polyethylene carbonate (PEC) as alternatives to PEO to address issues with crystallization and oxidative stability, respectively. Composite electrolytes are fabricated by blending bulk polymer with LiTFSI and LLZO powders. We have formed rubbery PEGMA-based composites with comparable conductivities (~10-7 S/cm at room temperature, 70 vol% polymer, 10:1 ethylene oxide:lithium). Lithium symmetric cycling was observed to be stable over 250 hours at 1C. We have also recently formed stand-alone PEC based composites with high conductivities (~10-6 S/cm at room temperature, 60 vol% polymer, 10:1 ethylene carbonate:lithium). Investigations into the origin of this high conductivity and measurements of electrochemical stability are currently underway.