bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the Ti Content on the Electrochemical Performance and Surface Properties of (La0.6Sr0.4)0.99Co1−
xTixO3−

δ
Oxygen Electrode
Authors: Heinsaar Alar , Kivi Indrek , Moeller Prit , Kooser Kuno , Käämbre Tanel , Aruväli Jaan , Lust Enn , Nurk Gunnar
Published: July 2021

Mixed ionic and electronic conducting (MIEC) oxides are being used as solid oxide fuel cell (SOFC) electrode materials [1, 2]. La1−
xSrxCoO3−

δ
(LSC) oxygen electrode has perovskite-type (ABO3) structure. The properties of these materials are determined by chemical composition, crystallographic structure and oxidation state of B-site elements. These electrode materials have good catalytic activity towards oxygen reduction reaction and oxide ion oxidation, but they have limited durability if carbon dioxide or humidity are presented in the electrode gas compartment. It is important to increase the long-term durability of these electrode materials at natural gas conditions, i.e. in gas from the external environment with micro-concentrations of impurities like water and carbon dioxide [3, 4, 5].

The SOFC oxygen electrode powders with different stoichiometry ((La0.6Sr0.4)0.99Co1−
xTixO3−

δ
, x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) were prepared by using the thermal combustion method [6]. X-ray diffraction (XRD) analysis was used to characterize the crystallographic structure of the synthesized powders. Symmetrical cells for Electrochemical Impedance Spectroscopy (EIS), Focused Ion Beam Time of Flight Secondary Ions Mass Spectrometry (FIB-TOF-SIMS) and X-Ray Photoelectron Spectroscopy (XPS) were made using synthesized powders. Prepared symmetrical cells were characterized at different temperatures, potentials, gas compositions i.e. conditions.

Systematic impedance analysis showed that materials with bigger cation (Ti4+), doped into the LSC B-site, increase the material long-term stability against impurities like carbon dioxide and water. As a result of the work, the optimal amount of dopant (Ti4+) was found, which increased the stability of the material in the environment with impurities.

[1] C. Singhal, K. Kendall (Eds.), High-Temperature Solid Oxide Fuel Cells: Fundamentals, Design and Applications, Elsevier, Oxford, (2003).

[2] Weber, E. Ivers-Tiffée, J. Power Sources 127, 273 (2004).

[3] Kivi, J. Aruväli, K. Kiresimäe, A. Heinsaar, G. Nurk, E. Lust, J. Electrochemical Society, 160, F1022 (2013).

[4] Kivi, J. Aruväli, K. Kirsimäe, P. Möller, A. Heinsaar, G. Nurk, E. Lust, J. Solid State Electrochem, 21, 361 (2017).

[5] P. Jiang, Int J. Hydrogen Energy, 44, 7448 (2019).

[6] P. Bansal, Z. Zhong, J. Power Sources, 158, 148 (2006).
Surface Modification and the Long-Term Performance Stability of Ca Doped LaCoO3 SOFC Electrodes
Authors: Sezer Mehmet , Ozdemir Okan , Colakerol Arslan Leyla , Buyukaksoy Aligul
Published: July 2021

Development of solid oxide fuel cells highly depends on the improvement of the long-term performance stability of cathode components. In our recent study, impressive activity was detected for thin film La0.6Ca0.4CoO3 (LCC) electrodes, which were fabricated by cost-effective polymeric precursor methods (1). However, significant performance degradation, i.e., 26 times increase in area specific resistance (ASR), upon long-term exposure to 700 °C, originating from changes in surface chemistry, such as; CaO + La2O3 segregation, was observed. In the present study, to enhance the performance stability of LCC cathode, the electrode surface was modified by the oxides of its A or B-site cations, i.e., La, Ca and Co. This way, reduction of the driving force for surface segregation was aimed. Electrochemical impedance spectroscopy (EIS) measurements performed on symmetrical half-cells at 700 °C revealed that the application of the CaO overlayer did not significantly affect ASR, while CoOx or La2O3 deposition caused slight improvements. Upon prolonged exposure to 700 ° for 100 hours, the ASR increased by factors of 3.3, 2.5, and 2 in the cases of La-, Co- and Ca-oxides, respectively, corresponding to significant enhancement of the long-term stability (Figure 1). The mechanisms through which the long-term performance stability enhancements were attained was studied via X-ray photoelectron spectroscopy (XPS) measurements. Preliminary results suggest that surface modification, especially by the oxides of Ca and Co stabilizes the surface composition, which leads to a significant enhancement of long-term performance stability

Figure 1. Changes in normalized area specific resistances of LCC04 and La, Ca and Co-oxide modified LCC04 electrodes upon long-term exposure to stagnant air, at 700 °C.

Figure 1
Simulation and Analysis of Thermal Stress and Sintering Warpage of Planar Solid Oxide Fuel Cells
Authors: Lang Shaocheng , Zhang Jihao , Wu Mingtao , Zheng Jianmin , Zhao Xin , Xiao Liusheng , Sun Zaihong , Han Minfang , Yuan Jinliang
Published: July 2021

Solid oxide fuel cell (SOFC) is one of the new energy conversion technologies producing electricity and heat from fuel and oxidant through an electrochemical reaction. The high operating temperature has many advantages including high efficiency, flexible fuel adaptability and low emissions. However, it has also some drawbacks, e.g., thermal expansion mismatches among the involved materials, particularly when the temperature reaches around 1400 oC during the sintering process, which may cause non-uniform distribution of thermal stress and even further deformation and warpage observed in the cell manufacturing steps.

A three-dimensional CFD (computational fluid dynamics) simulation model is developed to study the thermal stress distributed in the sintered function layers of the anode-supported planar SOFC unit cells (10×10 cm2) using a finite element method. Five layers are included, i.e., cathode and its separation layer (GDC/LSCF, 70 µm), anode support and active layers (Ni/YSZ, 550µm), and electrolyte layer (YSZ, 30 µm) between them. In terms of the thermal stress and deformation, the predicted results are presented and discussed for the sintered unit cells with different angels located around the four cornels.

It is found that the maximum thermal stress occurs at the interface between the electrode and electrolyte; the magnitude and distribution of thermal stress at the interfaces are closely related to the material thermal properties; the maximum deformation about 13 mm in the thickness direction is predicted for the 90-angel shaped cornels at the sintering temperature 1400 oC, which is bigger than that for the case with the circular shaped cornels; the deformation magnitude depends not only on the maximum thermal stress, but also the difference between the maximum and minimum thermal stress. The findings and predicted results may be applied for optimization of design and sintering conditions for SOFC unit cells.

Acknowledgements

This work is supported by the National Key Research and Development Project of China (2018YFB1502204, 2018YFB1502203, 2018YFB1502205), the Ningbo major special projects of the Plan “Science and Technology Innovation 2025” (2018B10048).

Figure 1
Sputtered Thin-Film Solid Oxide Fuel Cells
Authors: Minh Nguyen Q. , Lee Yoon Ho , Tran Quang Tuyen , Ren Haowen , Fullerton Eric E. , Wu Erik A. , Meng Ying Shirley
Published: July 2021

An all sputter process has been developed to fabricate thin-film solid oxide fuel cells (TF-SOFCs) using conventional materials. The process involves sequential sputtering of cell components onto a porous substrate; for example, anode such as nickel-yttria stabilized zirconia (Ni-YSZ), followed by electrolyte such as YSZ, interlayer such as gadolinium doped ceria (GDC), and then cathode such as lanthanum strontium cobalt perovskite (LSC)-GDC onto porous substrate such as anodized aluminum oxide (AAO). Process conditions and sputtering procedures have been tailored and engineered to produce the components with desired structural characteristics, i.e., fully dense electrolyte and interlayer and porous anode and cathode. The porous electrodes show a columnar structure with branch-like nano-fibers. Sputtered TF-SOFCs exhibit superior performance at reduced temperatures; for example, peak power density of about 3.0 W/cm2 at 650○C on H2 for the cell Ni-YSZ/YSZ/GDC/LSC-GDC, peak power density of about 2.6 W/cm2 at 700○C on CH4 for the cell Ni-GDC/YSZ/GDC/LSC-GDC.
Computational Predictions of Upscaling Solid Oxide Electrochemical Reactor Performances By Pillared Electrolyte | Electrode Interfaces
Authors: Jang Inyoung , Alexander John , Kawale Shrikant , Kelsall Geoff
Published: July 2021

Increasing densities of electrode | electrolyte interfacial areas (and triple phase boundaries) of solid oxide fuel cells or electrolyzers (solid oxide electrochemical reactors, SOERs) offers one means of increasing performance, reproducibility and potentially decreasing cost. Three-dimensional (3D) structuring of those interfaces can be achieved by 3D printing, but modelling is required to optimize geometries. Using kinetic parameter values from the literature, COMSOL finite element software was used to predict effects of YSZ electrolyte (c.f. electrode) pillar geometries on SOER performance, relative to planar YSZ electrolytes. The modified geometries are based on yttria-stabilized zirconia (YSZ) electrolyte pillars on top of < 10 mm thick planar YSZ electrolyte, thereby increasing interfacial to geometric area ratios. Electrolyte layers have been inkjet printed on Ni(O)-YSZ substrate negative electrode precursors and porous lanthanum strontium manganite (LSM) positive electrode have been printed over the YSZ, after sequential sintering producing complete SOERs: H2O-H2 | Ni(O)-YSZ | YSZ-YSZ pillars | YSZ-LSM | LSM | O2.

Results will be reported showing that despite interfacial electrode | electrolyte areas being up scaled by factors of 10-100 - depending on pillar diameter (5-50 mm) and height (15-150 mm) - current densities were predicted to increase by only 70-100% due to increased current path length along the pillars, which increases ohmic potential loss relative to the faradaic impedance. Hence, predictions of enhancement depend strongly on the kinetic parameters of the electrode material.
Accelerating Aging Test on Solid Oxide Cell Interconnects
Authors: Daviran Samaneh , Poitel Stéphane , Montinaro Dario , Walter Christian , Herbrig Kai , Ouweltjes Janpieter , Van herle Jan
Published: July 2021

The degradation of metal interconnects (ICs) is one of the main lifetime limiting issues in Solid Oxide Cells (SOCs). Chromium oxide thermally grows on the substrate surface that causes ohmic loss and its vapors poison the oxygen electrode reaction (OER). Mn-based spinels are presently among the materials of choice to protect ICs to prevent Cr diffusion.

As the target lifetime is around 40000h, it is of interest to design accelerated ageing tests, under harsher than nominal operating conditions, to simulate the long-time ageing behavior at nominal conditions.

In this study, the performance of IC coatings was investigated with accelerated ex-situ corrosion ageing tests, in which the operating condition of the air-side interconnect was simulated. Temperature and humidity were selected as test variable parameters. Area Specific Resistance (ASR) and Cr depletion/migration were studied for the stressed conditions. Tests were carried out on stainless steel substrate with Mn-Cu-Oxide and Mn-Co-Oxide as protective coatings.

Ageing tests over 1000h at different temperatures (750-950°C) and humidity (above 15%RH) were run while monitoring the ASR of the samples. Fig. 1 shows the ASR results for the samples run at different temperatures and in dry condition. Based on Fig. 1a-e, it is observed that the ASR trends remain constant during the test time. Although 916°C is well above nominal operating temperature, the ASR showed constant value within a reasonable range. At a test temperature 950°C (Fig. 1f), the ASR behavior of samples containing Co-Mn Oxide protective coating is the same found for lower temperatures; however, a sharp ASR increase in Mn-Cu Oxide coated samples can be observed. Applying humidity to high-temperature conditions also may help to accelerate the test, and its results will be presented. SEM/EDX post-test characterization provides information on the scale morphology and helps to understand the different behaviors at different stressed conditions.

Keywords: SOC; interconnect; protective coating; ageing test; accelerating test; Cr diffusion; ASR;

Figure 1
Influence of Surface Modification Using a Rare Earth Element on Properties of Ferritic Stainless Steel Metallic Interconnects
Authors: Hong Jong-Eun , Kim Seung-Gi , Kim Hye-Sung , Joh Dong Woo , Lim Tak-Hyoung , Lee Seung-Bok , Park Seok-Joo , Song Rak-Hyun
Published: July 2021

Iron and chromium based ferritic stainless steels have been considered to be a promising material for the metallic interconnect of solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs). However they have a drawback of chromium evaporation led by a scale growth at the steel surface when exposed at a high temperature oxidation atmosphere, which results in chromium poisoning of the air electrode and subsequent performance degradation of SOFCs and SOECs. Application of a surface modification or protective coating onto the metallic interconnects has been introduced to prevent the degradation by mitigating the chromium evaporation. In this study, ferritic stainless steels modified with a rare earth element of neodymium was investigated on the properties of high temperature oxidation and electrical conductivity. Detailed analyses on phase formation, microstructure evolution, and area specific resistance were carried out to figure out effects of the surface modification on the steels. Accordingly, the surface modified steels revealed decrease in the area specific resistance which was led by the reduction of scale growth since the rare earth element altered the chromium oxidation behavior.
A New Design Using a Metal Wire Brush as the Current Collector of Micro-Tubular SOFCs
Authors: Shi Jixin , Fan Junhua , Wang Yuqing , Shi Yixiang , Cai Ningsheng
Published: July 2021

In this study, a novel current collecting method was designed and demonstrated by inserting a metal wire brush into the anode supported micro-tubular SOFC. The new design enables a close and stable contact between the wire and the inner wall of the anode which leads to a fine performance of the SOFC. Different kinds of metal wires were applied, where the copper wire brush (CWB) shows a better performance than the stainless steel wire brush (SSWB). At a temperature of 650℃ and a fuel feed of hydrogen, the SOFC using CWB can achieve a maximum power density of 278mW/cm2 and an ohmic resistance of 0.75 Ω∙cm2, which are both better than that of SSWB (226mW/cm2 and 0.89 Ω∙cm2). While the brush size has been approved to have little effect on the ohmic resistance and the electrochemical performance. The potential of the metal wire brush as a support for internal reforming catalysts is further verified in experiments. The metal wire brushes loaded with Pt and Ni catalysts can realize effective reforming of hydrocarbon fuels, which makes the new design potential to use methane, propane, butane and other fuels for power generation.

Key words: Micro-tubular SOFC; Current collecting; Metal wire brush; Internal reforming
Enhanced Gas Diffusion in Reversible Solid Oxide Cell Fabricated by Phase-Inversion Tape Casting
Authors: Kishimoto Masashi , Higuchi Kazuhiro , Seo Haewon , Masuyama Asuto , Iwai Hiroshi , Yoshida Hideo
Published: July 2021

Electrochemical characteristics of a hydrogen-electrode-supported solid oxide cell (SOC) fabricated by phase-inversion tape casting are experimentally evaluated in both fuel cell (FC) and electrolysis cell (EC) operations. Particular focus is on the effect of the microchannels formed in the hydrogen electrode on the gas diffusion performance in the electrode. Current-voltage and impedance characteristics are measured and compared with those obtained from an SOC fabricated by conventional tape casting technique. The activation resistance is found to be almost identical between the tested cells because both cells are fabricated with a spin-coated functional layer in the hydrogen electrode. On the other hand, the concentration resistance is significantly decreased in the cell fabricated by the phase-inversion tape casting because the microchannels in the hydrogen electrode enhances the gas diffusion performance. This is more remarkable when the cells are operated in diluted fuel composition and with higher current densities. The asymmetric behavior is observed in the current-voltage characteristics of the cells, meaning that the overpotentials in the FC and EC modes are not the same at the same FC and EC currents. The overpotential is found to be always larger in EC mode, however, the extent of asymmetry is reduced in the cell fabricated by the phase-inversion tape casting. This is mainly because the microchannels in the hydrogen electrode reduces the gas diffusion resistance associated with the steam transport in EC mode. Microstructure of the fabricated cells is also analyzed in micro- and nano-scale to quantify the structure of the microchannels formed in the hydrogen-electrode. The microchannels are initiated below the immersed surface during the phase-inversion process, and then grow towards the bottom of the layer. The average diameter of the microchannels increases, whereas its number density decreases. Also, the total porosity in the phase-inversion electrode is found to be almost the same as that in the conventional cell.
Praseodymium Manganate-Based Perovskites as Anode Materials for Fuel-Assisted Solid Oxide Electrolysis Cells
Authors: Yaremchenko Aleksey , Boiba Dziyana , Patrakeev Mikhail , Arias Serrano Blanca I.
Published: July 2021

Long-term degradation remains the main issue for the viability of solid oxide electrolysis cell (SOEC) technology as a practical hydrogen production system. The major specific degradation mechanism in SOECs relates to delamination phenomena at or near electrolyte/anode interface. The principle of so-called fuel-assisted electrolysis is to supply the carbon-containing species which can react with oxygen at the anode side thus bringing down the oxygen chemical potential at the electrolyte/anode interface and improving its stability. The present work is aimed at the characterization of PrMnO3-based perovskites for potential application as anodes in solid oxide fuel-assisted electrolysis cells.

Pr0.6-x
A0.4MnO3
±δ (A = Sr, Ca; x = 0 and 0.05) were synthesized by glycine-nitrate combustion technique. The characterization included XRD, SEM/EDS, XPS, dilatometry and thermogravimetry, measurements of electrical properties and oxygen nonstoichiometry. XRD analysis confirmed the formation of solid solutions with orthorhombic perovskite structure. The oxides exhibit negligible variations of oxygen content under oxidizing conditions, while reducing p(O2) below 10-4 atm results in oxygen losses from the lattice and reduction of Mn cations. The low-p(O2) stability boundary of the perovskite phase at 800°C corresponds to ~10-17-10-16 atm; the stability domain is wider for Ca-substituted compositions and narrows with introduction of A-site vacancies. Dilatometric studies confirmed a good thermomechanical compatibility with common solid electrolytes. The electrical conductivity of Pr0.6-x
A0.4MnO3
±δ ceramics is p-type electronic and decreases with reducing p(O2), but still exceeds 40-50 S/cm under anticipated oxygen electrode operation conditions. The electrochemical performance of Pr0.6-x
A0.4MnO3
±δ electrodes was evaluated in contact with yttria-stabilized zirconia solid electrolyte as function of relevant parameters (fabrication conditions, with and without buffer layers, with praseodymia or ceria-based additives).
Additive Manufacturing of Large Area SOC with Advanced Features
Authors: Lira Maritta , Kostretsova Natalia , Bernadet Lucile , Morata Alex , Torrell Marc , Tarancón Albert
Published: July 2021

The incorporation of electrochemical-based energy devices such as Solid Oxide Cells (SOC) to the renewable energy sector in the frame of a modern energy generation strategy could be beneficial, taking into account the opportunity to store renewable energy overproduction as hydrogen (SOEC operation mode) as well as to use, subsequently, this hydrogen as a fuel for energy generation in the same device (SOFC operation mode).

Nowadays, the common-used SOC manufacturing approaches, in most cases, meet the limits originated by the capabilities of the techniques to produce the ceramic components with more complicated geometries, in respect to planar or tubular shapes. To overcome these constrains, the additive manufacturing (AM), commonly referred as 3D Printing, could be applied for the production of the SOC-based devices with enhanced features.

The use of AM allows a high degree of design freedom and opens a wide field for fabrication of functional ceramics with high resolution of herarchical geometries, optimized through computational elements by CAD design and stereolithographic (SLA)ceramic printing. At the same time the AM, specifically the SLA in this work, allows the simplification of the whole SOC manufacturing process making it tunable in geometry and size opening a new trend for fabrication of large area SOC with enhanced features in terms of active area or other functionalities. In a more effective way in terms of time, cost and waste material reduction.

The enhancement of the performance of the SOC device has been proved due to the increase of the active area by the production of complex shaped electrolytes using the 3D Printing process. To demonstrate,its scalability, large area 3YSZ electrolytes (~60-70 cm2) with the advanced geometries were fabricated by stereolithography three-dimensional printer, to be implemented as an electrolyte-supported cell using YSZ composites with lanthanum strontium manganite (LSM) as a cathode and nickel composites as an anode, i.e. Ni-YSZ/3YSZ/LSM-YSZ.
Physical and Electrochemical Characterization of La0.25Sr0.25Ca0.40Ti0.95Ni0.05-xSnxO3–δ (x=0...0.05) Reversible Solid Oxide Cell Fuel Electrode
Authors: Maide Martin , Moeller Prit , Aruväli Jaan , Lust Enn , Nurk Gunnar
Published: July 2021

Redox stability and sulfur- or carbon tolerance of solid oxide fuel cell electrodes are deeply defined by the chemical composition of the materials 1-3. Therefore, much effort is invested in finding more chemically stable and electrochemically active materials. Generally, mixed ionic electronic conductor (MIEC) fuel electrodes offer better stability at the expense of lower electrocatalytic activity towards H2 and CO oxidation, whereas, exsolution of catalytically active nanoparticles may help increase the latter 4. Recently, excellent electrocatalytic performance has been demonstrated for lanthanum and calcium doped strontium titanate based MIEC materials in fuel cell and electrolysis modes 5,6.

In this study, chemical stability and electrochemical performance of tin and nickel co-doped strontium titanate MIEC electrode materials (La0.25Sr0.25CaxTi0.9Ni0.50-ySnyO3–δ) were studied. Preliminary characterization included chemical stability studies followed by electrochemical characterization of most stable materials.

All studied fuel electrode materials were synthesized using standard nitrate combustion method. All the single cells were prepared using commercially available 250 μm thick Zr0.89Sc0.10Ce0.01O2-
d (10Sc1CeSZ, Kerafol) electrolyte support and La0.6Sr0.4CoO3-
δ
(LSC) oxygen electrode. Fuel and oxygen electrodes were sintered for 5 hours at 950°C and 900°C, respectively. Scanning electron microscopy, X-ray diffraction, FIB-TOF-SIMS and ICP-MS methods were used to characterize materials. Electrochemical characterization was carried out at temperature range from 700 to 850 °C in various H2O, CO2, H2 and Ar inlet concentrations.

The chemical stability was greatly influenced by the A-site deficiency and B-site composition of the material as confirmed by comparing the FIB-TOF-SIMS data of as-synthesized and 100 hours reduced fuel electrode materials. Furthermore, as expected, a variation in Ni and Sn content resulted in large variations in studied single cell’s performances. Finally, the stability to the sulphur impurities in fuel electrode gas was investigated for some studied materials.

References:

S. Tao, J. T. S. Irvine, J. Electrochem. Soc., 151, A252-A259 (2004).

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

Q. X. Fu, F. Tietz, Fuel Cells, 8, 283 (2008)

G. Kim, S. Lee, J. Shin, G. Corre, J. T. S. Irvine, J. Vohs, R. J. Gorte, Electrochem. Solid State Lett., 12, B48 (2009).

A. Yaqub, N. K. Janjua, C. Savaniu, J. T.S. Irvine, Int. J. Hydrogen Energy, 40, 760 (2012).

A. D. Aljaberi and J. T. S. Irvine, J. Mater. Chem. A, 1, 5868–5874 (2013).
Design and Fabrication of a Functionally Gradient SOFC Electrode with Controllable Porous Microstructure
Authors: Dan Edward , Du Yanhai
Published: July 2021

A controllable and gradient porous ceramic structure is desirable for many applications including solid oxide fuel cells (SOFC), ceramic filters or gaseous component separation. There are numerous ways to fabricate porous ceramic structures, including the use of pore formers, particle size control or freeze casting. The process we used was string-coating. Strings with various materials’ coating and coatings on various strings could be a controllable element for assembling a planar or tubular ceramic microstructure. In this research, ceramic microtubes were made using removable templates covered by layers of ceramic materials using sol-gel technology. A low-cost device was designed and built for coating multiple layers of slurry onto templates efficiently. Tested templates included silk (single and triple strands), cotton thread, and angel hair pasta coated with 1, 5, 10, 15, 20, or 25 layers of slurry and then fired with a 5-stage heating cycle up to 1,100°C/1,450°C over a period of 20 hours. Samples were analyzed using a scanning electron microscope (SEM). Average diameters were calculated by measuring 30 diameters from different locations of each tube. The 20× and 25× coatings on the single silk strand, sintered at 1,450°C, resulted in the strongest and most density-uniform microtubes by decreasing the porosity. The single silk strand with 20× coating under 1,450°C firing formed a 25µm diameter hole and an average outer diameter (OD) of 39.90 µm with a standard deviation of 0.97 µm, while the 20× coating under 1,100°C resulted in an average 67.46 µm OD with a standard deviation of 1.14 µm. The 25× coating resulted in a 49.89 µm OD with standard deviation of 0.99 µm when fired up to 1,450°C. The success of this process set a foundation for assembling the individually controllable single microtubes to form ceramic planar or tubular shapes that their microstructure is controllable in terms of composition, pores size, porosity and connectivity.
Thermal Residual Stress and Failure Probability of Functionally Grade Ni-YSZ Anode of Solid Oxide Fuel Cells Using a Finite Element Analysis
Authors: Zhang Xi , Yan Zilin , Zhou Yexin , Zhong Zheng
Published: July 2021

Due to the differences of thermal expansion coefficient between the components in the solid oxide fuel cells (SOFCs), there is a large residual thermal stress in the fabrication process of the cell. In this study, the functionally graded (FG) Ni-YSZ anode design was introduced between Ni-YSZ support and YSZ electrolyte to mitigate the thermal residual stress in SOFC. In the current FG anode design, composition of Ni and YSZ was varied according the function of
φ
(Ni) =
k
(
t
/
H
)

n

, where
k
is a constant which is equal to the volume fraction of Ni in Ni-YSZ anode support layer,
t
is the distance to the electrolyte,
H
is the thickness of the FG anode layer and
n
is the exponential factor. In the numerical model, the FG anode layer was evenly divided into
m
sublayers. The porosity was set to a constant value of 0.3 and uniformly distributed in the anode. The residual stress of the anode was modeled as the thermal stress when the anode was cooled from the reduction temperature of 1200 oC to room temperature of 20 oC. Residual thermal stress was calculated by finite element method (FEM) using the commercial ANSYS package. Failure probability of functionally graded SOFC was evaluated using the classic Weibull probability model.

The effects of sublayer number
m

=

(1, 2, 3, 4), exponential factor
n

=

(0.25, 0.5, ..., 4.0) and gradient layer thickness
H

=

(20, 30, 40 μm) on the stress and failure probability of functionally graded SOFC are discussed. The calculation results show that the FG anode layer can obviously reduce the stress, and effectively decrease the stress concentration between electrode and electrolyte. The failure probability can be reduced by two orders of magnitude at most as compared with the conventional SOFC. Under the same exponential factor
n
, appropriately increasing the number of sublayers
m
can reduce the stress of the gradient layer. The sublayers number
m

=
2 is a suitable value. With the increase of the thickness of the gradient layer, the anode failure probability increases. The research provides a reference for further optimizing the stress in SOFC.
Synthesis of Borate Doped La10Ge6O27: Confirming the Presence of a Secondary Conducting Pathway
Authors: Thomas Samuel W , James Matthew Samuel , Stockham Mark P , Deakin Joshua , Jarvis Abbey , Slater Peter R.
Published: July 2021

Lanthanum silicate/germanate apatite materials have attracted significant interest as Solid Oxide Fuel Cell electrolytes due to their high oxide ionic conductivity at lower temperatures (500-800 ⁰C). In these structures, oxide ion conduction is due to interstitial pathways associated with the high oxygen excess within the structures. Therefore, cation doped La8+xA2-x(M6-xBxO4)O2+x/2 (A = Ca, Sr, Ba; M = Si and Ge; B = Mg, Ga, Al, Zn, B) have been reported to increase oxide ion conductivity via the introduction of excess oxide ions.[1-3]

Whilst apatite silicate has higher conductivities at lower temperatures due to lower activation energies, apatite germanates can achieve higher oxygen excess and therefore higher conductivities at elevated temperatures. However, in increasing oxygen content there is a change in symmetry from hexagonal to triclinic leading to a subsequent reduction in conductivity.[4] Previous studies have shown the issue may be overcome by the incorporation of Y doping e.g La8Y2GeO6O27 which leads to stabilisation of the higher conducting hexagonal phase.[5]

Herein, we demonstrate the successful incorporation of borate into La10-xYxGeO6O27 and show that it also stabilises the higher conducting hexagonal form. We show that B can be doped into both the Ge site and the oxide ion channels. Interestingly, the conductivity of samples with borate in the channels (which would be expected to block channel oxide ion conductivity along the c direction) is still reasonably high, which supports suggestions that there is significant conduction perpendicular to the channels in these apatite germanates.

[1] A Orera and P R Slater, Chem. Mater 2010 22 675-690

[2] P M Panchmatia, A Orera, G J Rees, M E Smith, J. V. Hanna, P. R. Slater and M. S. Islam, Angew. Chem. Int. Ed, 2011 50 9328-9333

[3] E Kendrick, M S Islam and P R Slater, J. Mater. Chem 2007 17 3104-3111.

[4] M S Chambers, P Chater, I R Evans and J S Evans, Inorg. Chem., 2019 58(21)14853-14862,

[5] A Najib, J. E. H. Sansom, J. R. Tolchard, P. R. Slater and M. S. Islam, Dalton Trans., vol. 19, pp. 3106-3109, 2004.
Y/Zr/NiO-Ceria/Silica Nanocomposite Anodic Cermets Support Direct Ethanol SOFC
Authors: Eduok Ubong
Published: July 2021

Several inherent challenges accompany direct conversion of primary fuels (e.g. ethanol) at elevated temperatures and these problems limit the applicability and efficiency of the solid oxide fuel cell (SOFC) technology. In fact, a pressing problem is the fuel dehydrogenation of standard nickel-based anode cermet. In the present study, the contribution of ceria/silica nanoparticles acting as dopants toward the stability of nickel oxide (NiO) functionalized anodic layer for direct ethanol SOFC was investigated. Two dopants were fabricated from fused molten nanocomposite consisting of combined ceria and silica nanoparticles (4:1 volume ratio) with 5 wt% Y or Zr bound to NiO. After synthesis, both nanocomposites were characterized using appropriate techniques (Scanning Electron Microscopy, SEM, X-ray Photoelectron Spectroscopy, XPS, and X-ray Diffraction, XRD, techniques). All tests were conducted in fixed bed reactors for ethanol fueled SOFC. The Zr containing dopant altered the catalytic properties of these modified ceria/silica supports toward ethanol steam reforming compared to Y, while changes in electronic transport properties were also observed for both Y/NiO and Zr/NiO ceria/silica nanocomposites. The dopant with Zr also exhibited significant oxygen storage capacity and electronic conductivity compared to Y. In summary, these ceria/silica-based cermets acted as novel and effective anode materials for ethanol steam reforming.

Keywords:
Solid oxide fuel cell (SOFC); Ceria dopants; Silica-based cermets; Direct ethanol SOFC.
(Plenary) U.S. DOE EERE Activities in High Temperature Electrolysis and Reversible Fuel Cells
Authors: Peterson David , Stetson Ned , Papageorgopoulos Dimitrios , Gibbons William T , Randolph Katie
Published: July 2021

The Hydrogen and Fuel Cell Technologies Office (HFTO) within the U.S. Department of Energy’s (DOE) Office of Energy Efficiency and Renewable Energy (EERE) supports a range of solid oxide-based research, development, and demonstration efforts that fall under the areas of high temperature electrolysis (HTE) and reversible fuel cells (RFCs). These efforts range from earlier stage R&D on cell components to demonstrating early system technology. Particularly when used in conjunction with high temperature process heat, HTE technology shows promise for highly efficient, cost effective, sustainable hydrogen production at high volumes. This potential has led to its inclusion in multiple HFTO initiatives, including two national lab-led consortia. HTE is one of four pathways being supported under DOE’s HydroGEN Energy Materials Network (EMN) Consortium on Advanced Water Splitting Materials (AWSM) for H2 production. The HydroGEN EMN offers an extensive collection of materials research capabilities at 5 core national laboratories for addressing AWSM R&D challenges in efficiency, durability, and cost. HydroGEN focuses on next generation materials including proton conducting ceramics and metal-supported cell architecture for HTE. H2NEW (H2 from Next-generation of Electrolyzers of Water) is a recently launched national lab consortium focused on overcoming technical barriers to enable affordable, durable, and efficient low- and high-temperature electrolyzers to achieve <$2/kg hydrogen production. Unlike HydroGEN, the emphasis is not on new materials development but on addressing components, materials integration, and manufacturing R&D. Durability is the most critical, initial focus of the H2NEW HTE effort.

HTE also has a role in DOE’s H2@Scale energy system vision. This initiative is bringing together diverse stakeholders to advance affordable wide-scale hydrogen production, transport, storage, and utilization to unlock revenue potential and value across multiple sectors and applications. The use of low-cost electricity to affordably split water into hydrogen and oxygen is central to implementation of the H2@Scale concept. Reversible fuel cells also have a role in H2@Scale as well as DOE’s Energy Storage Grand Challenge as a promising technology for long duration energy storage. RFC stack and system technical targets to help guide ongoing and future R&D efforts were recently developed. In addition to an overview of these initiatives including the role solid oxide technologies will play, highlights of HFTO-supported R&D and analysis work from the cell to system level for both HTE and RFCs will be provided.
Optimization of Methane Reforming for High Efficiency and Stable Operation of SOFC Stacks
Authors: Liu Yaodong , Lyu Zewei , Han Minfang
Published: July 2021

Abstract: Solid Oxide Fuel Cells (SOFCs) is an efficient and clean pathway to generate electricity. In addition to hydrogen, SOFCs also provide the possibility for the utilization of a variety of carbon containing fuels. However, the application of carbon-based fuels in SOFC remains to be further studied. In this study, an external reformer was used to create appropriate reforming syngas from methanol and avoid carbon deposition. The performance and the efficiency of SOFC were researched with methanol-reformed syngas as fuel. The thermodynamic calculation and experimental work of water vapor reforming reaction of methanol fuel were carried out to study the composition of reforming gas under different temperature and steam-carbon ratio conditions, where the experimental results and the computational results matched well. The mole fraction of hydrogen in reformed syngas was about 55% within the temperature of 700~800 ℃, nevertheless, this value reached 70% if the moisture was removed. Therefore, the reformed syngas should be applied to SOFCs before being condensed and dried. Based on the comparison between the experimental results and the calculated ones, the appropriate components were selected to prepare the reforming syngas, feeding into the anode of SOFC to test the performance and the efficiency. Optimal temperature and steam-carbon ratio conditions for methanol vapor reforming were obtained. Under these conditions, the power density of SOFC exceeded 0.4 W/cm2 and the efficiency reached 50% (LHV). The main conclusions confirmed the high efficiency and feasibility of the methanol-fueled SOFC power generation system.
In-Situ Measurement of Residual Stress in Solid Oxide Fuel Cells
Authors: Yashiro Keiji , Komaya Takumi , Ruhma Zaka , Watanabe Satoshi , Sato Kazuhisa , Kawada Tatsuya
Published: July 2021

Introduction

Solid oxide fuel cells (SOFCs) are attracting attention as highly efficient energy conversion devices. However, durability and mechanical reliability are issues. To improve durability and mechanical reliability, it is essential to evaluate the residual stress generated in the constituent materials, especially the residual stress generated in the electrolyte. While residual stress is measured by various methods, the optimum measurement method has not been established yet. The purpose of this study is to evaluate the residual stress of the cell using in-situ cosα method, which has an advantage in measurement speed and easy handling.

Experiment method

High-temperature x-ray stress measurement was performed as a quantitative evaluation method for mechanical behaviors. A portable X-ray residual stress measuring device μ-X360s manufactured by Pulstec Industries was used. The cos α method, which is faster and easier than the sin2ψ method, was used for high-temperature X-ray stress measurement. In the cosα method, the Debye ring is acquired by a two-dimensional detector, and the stress is calculated from the difference between the stress-free Debye ring and the Debye ring of the measurement sample. High temperature chamber was designed and prepared for high temperature x-ray stress measurement. A capton film is used to separate outside and measurement atmosphere. In addition, the measurement position can be adjusted by moving stage.

Commercial sofc cells (Ningbo SOFCman cell and Elcogen) were used to compare the residual stress during the various operation procedures.

Results and discussion

Fig. 1 shows the difference in change in residual stress of YSZ electrolyte depending on the structure of the anode. Anode of Ningbo SOFCman cell has small porosity, while anode of Elcogen cell has large porosity. We measured changes in residual stress during heating, anode reduction, and reoxidation processes.

The Elcogen cell was reduced much faster than Ningbo cell, because hydrogen gas can diffuse more easily in anode due to higher porosity. Therefore, residual stress of Elcogen cell steeply changed after hydrogen introduction. Then, the residual stresses after anode reduction were completely different in these two cells at room temperature. Compressive stress of 800 MPa remained in the electrolyte of Ningbo cell. On the other hand, less compressive stress of 400 MPa remained in the electrolyte of Elcogen cell. The temperature dependence of residual stress is also different in the two cells. The deformation of the cell after reoxidation was also completely different. Ningbo cell was deformed convexly toward the anode side, although Elcogen cell was hardly deformed. The difference may come from the difference in porosity of anode.

Fig. 1 Circumferential residual stress of YSZ during reoxidation heating in 20％O2-N2 and SEM images of anode structures.

Figure 1
Operando Thermal Imaging Study of Internal Partial Methane Oxidation in Ni-YSZ Anodes of Commercial SOFCs
Authors: Tsoi Stanislav , Maza William A , Kirtley John , Steinhurst Daniel , Eigenbrodt Bryan , Pomeroy Elias D , Walker Robert A. , Owrutsky Jeffrey
Published: July 2021

Thermal imaging is employed to study internal partial methane oxidation in a Ni-YSZ anode of a commercial, button-style solid oxide fuel cell at 800 °C in real time. When a stoichiometric 2:1 mixture of methane and oxygen is delivered to the anode, thermal imaging reveals formation of two distinct zones on the exposed surface of the anode: a smaller zone of increased temperature near the fuel delivery inlet and a larger zone of decreased temperature occupying the rest of the anode. We assign the former to exothermic complete oxidation of some methane to steam and carbon dioxide and the latter to endothermal reforming of the remaining methane with the steam and carbon dioxide generated in the hot zone. Simultaneous detection of catalytic products using mass spectrometry indicates that when combined the two sequential reactions convert almost 80% of the delivered methane, with the main products being carbon monoxide and hydrogen. Cell polarization during partial methane oxidation delivers an oxide ion flux to the anode-electrolyte interface. As the oxide flux is significantly lower than the oxygen gas flux delivered in the methane and oxygen mixture, the former is used to probe the catalytic products of partial methane oxidation. Our results reveal negligible amounts of unreacted methane and accumulated carbon on the anode surface during the partial oxidation process.
Shrinkage Behavior, Thermal Expansion Behavior, and Electrical Conductivity Study of Samarium Doped Ceria Electrolytes
Authors: Lakhanlal Lakhanlal , Dasari Hari Prasad , M.B. Saidutta
Published: July 2021

Ceria-based electrolytes generally have high sintering temperatures (~1500 °C)1,2, which increases the cell fabrication cost and decreases the mechanical stability of the cell due to rapid grain growth. In this work, the Ce0.9Sm0.1O2 (SDC) electrolyte is synthesized by microwave-assisted co-precipitation method using ethanol as a solvent. The sintering behavior of the green compact is studied using a dilatometer. Linear shrinkage and shrinkage rate behavior study shows a low sintering end temperature (1200 °C) and a final relative density of ~92%. A maximum linear shrinkage of -15.70% is observed at 1200 °C. A uni-modal shrinkage rate curve is seen, which confirms uni-modal pore size distribution in the powder. After 1388 °C, a dedensification is observed (+ 0.29% linear shrinkage), which might be associated with the reduction of Ce4+ to Ce3+ (please see Figure 1). Initial sintering results suggest that the synthesis method used has significantly lowered the SDC electrolyte's sintering temperature. Although the densification is completed at 1200 °C, the microstructure may change with further increase in the sintering temperature, affecting electrical conductivity. Inspired by the initial results, a detailed study on the effect of sintering temperature (1200 °C to 1500 °C) on the microstructure and electrical conductivity of SDC will be carried out and presented in the paper.

S. Medisetti et al., Nano-Structures & Nano-Objects, 11, 7–12 (2017) https://www.sciencedirect.com/science/article/pii/S2352507X16301275.

G. Accardo et al., J. Appl. Biomater. Funct. Mater., 14, 35–41 (2016) https://journals.sagepub.com/doi/abs/10.5301/jabfm.5000265.

Figure 1
Deconvolution of Gas Diffusion Polarization in Ni/Gadolinium-Doped Ceria Fuel Electrodes
Authors: Grosselindemann Cedric , Russner Niklas , Dierickx Sebastian , Weber Andre
Published: July 2021

Electrochemical impedance spectroscopy and the subsequent impedance data analysis by the distribution of relaxation times (DRT) represent a powerful method to unfold electrochemical processes in solid oxide cells. This approach has been successfully demonstrated for electrolyte [1, 2] as well as anode-supported [3] solid oxide cells exhibiting a nickel / yttria-stabilized zirconia (Ni/YSZ) fuel electrode. Applying this methodology, all physicochemical loss processes occurring in the cells could be identified by their relaxation frequencies and subsequently quantified by means of CNLS-fitting.

However, in the case of cells exhibiting a Ni/Gadolinium-doped ceria (Ni/CGO) fuel electrode, an unambiguous process assignment in the DRT has not been feasible up to now, since the charge transfer and gas diffusion overlap in the spectrum [4, 5]. The latter is caused by the oxygen non-stoichiometry of CGO, which results in a large chemical capacity, shifting the relaxation frequency of the charge transfer process towards lower relaxation frequencies. The resulting overlap of charge transfer and gas diffusion process in the spectrum impedes a direct deconvolution of these two processes [6].

Facing this challenge, we here present a solution of isolating and quantifying the gas diffusion process at the fuel electrode with the help of ternary fuel mixtures exhibiting different gas diffusion coefficients. The gas diffusion coefficients of hydrogen and steam were altered by changing the inert gas component between nitrogen and helium respectively. As the two gas mixtures exhibit identical reactant and reaction product concentrations, the charge transfer polarization is not affected. The differences in polarization resistance R
pol, which become visible in figure 1, are solely caused by the differences in gas diffusion polarization [2].

In this contribution the detailed procedure to quantify the gas diffusion polarization and an effective gas transport parameter predicting the gas diffusion resistance for arbitrary fuel mixtures are introduced. Furthermore, the applicability of this approach for the parameterization of a zero-dimensional cell model [3] for a solid oxide cell with Ni/CGO fuel electrode will be presented.

References:

[1] Schichlein et al., J. Appl.
Electrochem., 32, 875 (2002).

[2] Sonn et al., J. Electrochem.
Soc., 155 (7), B675 (2008).

[3] Leonide et al., J. Electrochem.
Soc., 155 (1), B36 (2008).

[4] Weber et al., ECS Trans., 77 (10), 141-147 (2017).

[5] Riegraf et al., ChemSusChem, 10, 587 (2017).

[6] Riegraf et al., J. Electrochem.
Soc., 166 (13), F865 (2019).

Figure 1: (a) Nyquist-plot and (b) DRT of the impedance spectra of two ternary gas mixtures with the inert gases nitrogen and helium respectively (T = 852 °C, OCV-conditions, gas composition: 0.1 atm H2, 0.05 atm H2O, 0.85 atm inert gas).

Figure 1