bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the Bias Substrate Power on the GDC Buffer Layer
Authors: Breaz Elena , Aubry Eric , Billard Alain , Coton Noelia , Coquoz Pierre , Pappas Andrée , Diethelm Stefan , Ihringer Raphaël , Briois Pascal
Published: February 2020

Nowadays, the researchers that are working on the SOFC technology, are agree that it is necessary to decrease the operating temperature at 700°C(650-750 °C) of IT-SOFC technology, which currently is around 850-900°C for electrolyte supported cell used by the three main operators –Bloom, Hexis and Sun Fire. At this temperature the reactivity and the component cost of the cell decrease. Nevertheless, some interactions between the conventional electrolyte material (YSZ) and the cathode material (lanthanum based) are still present and it is necessary to include a ceria buffer layer to avoid the possible formation of an insulating pyrochlore structure La2Zr2O7 layer at the electrolyte-cathode interface. In ceria family, the best material regarding the ionic conductivity is the samaria doped ceria. However, the gadolinia doped ceria is the most employed from the cost point of view and the availability of gadolinium in comparison with samarium. This buffer layer avoids the reactivity between electrolyte and cathode, and presents a good anionic conductivity. It must be dense, thin and adherent on electrolyte, in order to be suitable for the surface treatment process.

In this paper, we present some recent results obtained on the gadolinia doped ceria coatings deposited by magnetron sputtering from metallic targets in argon-oxygen reactive gas mixtures with different substrate bias voltage. After a description of the experimental device, a first part will be dedicated to their chemical, microstructural and structural characterization (SEM, XRD,…) in relation with the magnetron sputtering deposition parameters. In a second part, the ionic transport characteristics of the half cell (Ni-YSZ/YSZ/GDC) will be investigated via impedance spectroscopy measurements performed at various temperatures up to 800°C under Ar-H2 gas mixtures. Finally, a complete cell test ((Ni-YSZ/YSZ/GDC/LSC) was performed with the Fiaxell Open Flanges test bench.

This study is carried out within the framework of the European territorial cooperation program INTERREG V A France-Switzerland. It has benefited from financial support from the EU through the European Regional Development Fund (ERDF- € 139,176) and the Swiss Confederation's contribution of CHF 134,173
Solid Oxide Electrolyzer Stack with 20,000 h of Operation
Authors: Fang Qingping , Blum Ludger , Menzler Norbert H. , Stolten Detlef
Published: February 2020

One of the critical challenges for application of solid oxide cell (SOC) technology is the long-term stability of the complete system and/or single component. Despite of different debating accelerating methods, the time and cost consuming endurance tests of stacks and cells under relevant conditions are still necessary for reliable degradation analysis and lifetime prediction. In parallel to the stationary solid oxide fuel cell stack tests (>34,000 h), a test with a two-layer solid oxide electrolyser stack in JÜLICH’s F10-design was started on September 2014 (still in operation as of 26.01.2017). The short stack consists of Ni/YSZ-supported cells (ASCs in fuel cell mode) with LSCF air electrode (La0.58Sr0.4Co0.2Fe0.8O3-δ) and 8YSZ (8 mol-% yttria-stabilized zirconia) electrolyte. A gadolinium-doped ceria (GDC) (Ce0.8Gd0.2O1.9) barrier layer was deposited between 8YSZ and LSCF by means of physical vapor deposition (PVD).

The stack was mainly characterized in a furnace environment in electrolysis mode, with 50% humidified H2 at 800 °C. The endothermic electrolysis operation was carried out with a current density of -0.5 Acm-2 and steam conversion rate of 50%. Electrolysis at lower temperatures (i.e. 700 °C and 750 °C) and fuel cell operation (with 0.5 Acm-2 and fuel utilization of 50%.) at 800 °C were also carried out shortly (<2000 h each) for comparison. After altogether ~20,000 hours of operation, the voltage and ASR degradation rates during electrolysis at 800 °C (8000~20,000 h) are ~0.4%/1000h and 3%/1000h, respectively. Electrochemical impedance spectroscopy (EIS) and analysis of the distribution function of relaxation times (DRT) showed that the degradation was primarily due to the increase in ohmic resistance. An increasing polarization in fuel electrode in one of the layers was also observed during the last 2000 h of operation, most likely due to the increased leakage rate inside the stack.

The stack is planned to be operated for another 2000 h before post mortem analysis. Stack performance and degradation analysis under different working conditions, together with preliminary post analysis will be presented.
Field Demonstration of a Novel Reversible SOFC System for Islanded Microgrid Energy Storage
Authors: Mermelstein Joshua , Cannova Catherine , Cruz Michael , Anderson Bill
Published: February 2020

The high cost and energy security of importing fuel to islanded grids and communities has led to a growing need to generate power onsite with alternative and renewable energy technologies while reducing logistics costs of importing electrical power. The ability to provide independence, endurance, reliability, and resilience of power compels both remote and critical infrastructure loads to integrate greater capabilities into their microgrid systems. However, grid operators are being faced with the challenges of variability and intermittent energy production from renewables. Therefore, energy storage has become a critical component to balance micro and utility grids, improve efficiency, reduce fuel consumption, enable localized grid independent energy secure power in cases of emergencies or unreliable traditional grid use, and provide critical power in the event of power outages. There has been particular interest in reversible solid oxide fuel cells (RSOFCs) in the energy sector for electricity, energy storage, grid stabilization and improvement to power plant system efficiency due to favorable thermodynamic efficiencies of high temperature steam electrolysis. With funding from Naval Facilities Engineering Command and Expeditionary Warfare Center (NAVFAC EXWC), Boeing’s Advanced Technologies Program, using Sunfire fuel cell technology, has developed the largest ever fully integrated grid tied RSOFC system that uses sunlight and sea water to generate and store energy with no logistical tail. In this system, excess grid energy or curtailed power generated by renewables is sent to the system operating in electrolysis mode to produce H2. The H2 is stored and then used in the system’s fuel cell mode to provide supplemental power to the grid during peak hours or as needed. The system was designed to run off of sea water for cooling and water feed for electrolysis via an internal desalination unit or via the water recycle system. As part of this program, Boeing has developed a H2 storage and compression system, power distribution system, and master controller to interface with the fuel cell subsystem developed by Sunfire. Previous results showed that the system exceeded expectations with an electrolysis efficiency of > 80% LHV and an overall system efficiency of 60% LHV with compression and liquid water feed. The system has been shipped to Pearl Harbor on the island of Oahu, Hawaii to undergo a 6 month demonstration in the field on a working island microgrid. The intent of this demonstration is to validate the opportunity to insert reversible fuel cell systems with greater power generation (e.g. up to 1 MW) into microgrids on both remote islands and expeditionary applications. This paper will discuss test results and challenges of demonstrating a RSOFC system in island microgrid environments. It will also discuss how the RSOFC system fits into the overall microgrid concept for NAVFAC and helps to address a logistic free hydrogen economy in remote areas.
LaNi0.6Fe0.4O3 as Cathode Contacting Material: Effect on Anode Supported Cell Performances
Authors: Spotorno Roberto , Piccardo Paolo , Costa Rémi , Han Feng , Schiller Guenter
Published: February 2020

In planar solid oxide fuel cell (SOFC) stacks ohmic losses are introduced at the interface between the electrodes and current collectors, especially in the cathodic compartments, due to the contact inhomogeneity. The porosity of the electrodes and geometrical issues linked to the shape of the interconnects are factors resulting in the reduction of the contact surface between such components. Contacting layers are often applied between the cathode and the interconnect in order to minimize such issues ensuring a uniform current collection along the electrode area. This leads to proper operation of the cells increasing the performances in terms of power output and mitigating their degradation rate.

In this work, LaNi0.6Fe0.4O3 (LNF) powders have beensynthesized by sol-gel methods and used to prepare a contacting paste. A testing setup, developed to test anode-supported cells with different contacting geometries, has been used to investigate the effect of LNF contacting paste between the cathode and the current collector. The cell performances revealed comparable results compared to those measured using a state-of-art La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) contacting paste, even showing better stability over time. Cell performances have been investigated by means of current-voltage curves. Electrochemical impedance spectroscopy has been used to distinguish the loss contribution within the investigated system and to measure their evolution over time. To confirm the observed performance evolution, microstructural changes and migration of elements have been characterized post-experiment by means of scanning electron microscopy-energy dispersive X-ray and X-ray diffraction techniques.
Changes in SOFC Cathode Crystallographic Structure Induced by Oxygen Deficiency in Cathode Room
Authors: Kivi Indrek , Aruväli Jaan , Nurk Gunnar , Lust Enn
Published: February 2020

Stationary solid oxide fuel cell systems (SOFC) are highly efficient chemical energy conversion systems generating electricity and high quality heat. SOFC devices should be usable during over 40 000 hours and at least 100 thermal cycles. In this study, the changes of unit cell of cathode materials as a function of current density, p
O2 and temperature were analyzed as a risk factor to increase the degradation rate of cathode electrode, during the cell working time.

Reversible changes in the lattice parameters of SOFC cathode were observed depending on the temperature (T) and oxygen partial pressure (p
O2) applied. The cathode potential, T and p
O2 noticeably influences the unit cell volume, thus, the oxygen stoichiometry and concentration of vacancies.

The electrode structure (porosity) has strong influence to the change kinetics of crystallographic parameters of cathode at in-situ element operating conditions. By polarizing the cathode electrode cathodically, the activity of electrode increase and the molecular oxygen concentration near the electrode surface decrease. Decrease of oxygen concentration in the porous cathode matrix causes the expansion of lattice parameter of cathode material. The electrode material (LSC and GSC) lose oxygen, Co4+ reduces to Co3+ and because of that unit cell expands.

Only slight influence of oxygen partial pressure and potential to the crystallographic parameters of LSM (La0.6Sr0.4MnO3
−
δ) was registered. At the same time for LSC (La0.6Sr0.4CoO3
−
δ) and GSC (Gd0.85Sr0,15CoO3
−
δ) the crystallographic unit cell volume was a function of electrode polarization as well as the oxygen partial pressure. There is no remarkable vacancy formation detectable with HT-XRD in LSM cathode lattice caused by electrode polarizations applied.

Thermochemical crystallographic expansivity study of LSM, LSC and GSC cathodes with in-situ HT-XRD method gives valuable experimental data about the crystallographic changes caused by changes in operating parameters like cell potential, temperature, and oxygen partial pressure in cathode compartment and therefore helps to understand thermomechanical and degradation behavior as well as redox behavior of B site element (Co) as a function of different conditions applied for SOFC cathode.

Figure 1. Selected segment from XRD pattern for LSCO and GSCO cathode at electrode potentials 0 and -0.9 V vs Pt/Pt/O2, respectively.

Figure 1
Fabrication and Characterization of High Performance Intermediate Temperature Micro-Tubular Solid Oxide Fuel Cells
Authors: Ren Chunlei , Gan Yun , Lee Myongjin , Yang Chunyang , He Fei , Jiang Yanmei , Dong Guohui , Green Robert , Xue Xingjian
Published: February 2020

A phase inversion-based dual-layer co-extrusion approach was advanced to fabricate micro-channel array structured micro-tubular

solid oxide fuel cells (MT-SOFCs). The inner graphite layer was used as a sacrificial layer to eliminate the middle sponge-like layer

and inner surface dense skin layer,which were normally formed using the single layer extrusionmethod. As a result, themicro-channel

array generated in the outer layer was a more open structure and facile fuel/gas diffusion was obtained. The fuel/gas permeability of

such an anode substrate Ni-Ce0.8Sm0.2O1.9 (Ni-SDC) was ∼9 times that of an anode substrate fabricated using the phase inversionbased

single layer extrusion method. The open circuit voltages (OCVs) of the corresponding cell Ni-SDC/SDC/PrBaCo2O5+δ were

0.89 V–0.85 V at 500–600◦C, much higher than those of other SDC electrolyte based MT-SOFCs. The peak power density of the

cell was ∼1484 mW cm−2 at 600◦C, approximately 1.5 times that of a similar cell with an anode substrate fabricated from the single

layer extrusion method. This is also the highest performance among the SOFCs with the same material system in open literature.

The fuel utilization rate was also significantly improved in different degrees depending on the supplied inlet fuel flow rates.
Design and Performance Characteristics of Portable, Self-Sustaining and Quick-Start Micro-Tubular SOFC Stacks
Authors: Mushtaq Usman , Park Seok-Joo , Song Rak-Hyun , Lim Tak-Hyoung , Lee Jong-Won , Lee Seung-Bok
Published: February 2020

Micro-tubular solid oxide fuel cells (MT-SOFCs) have diverse applications including transportation, critical military missions, auxiliary power units or portable power generators. Especially portable power devices should be lightweight and quickly started, so that they have requirements of high thermal shock resistance, high power density per weight and self-sustaining operation. This work presents the design, fabrication methods and performance of multiple MT-SOFC stacks containing cells of 15cm2 active electrode area. Extruded Ni-8YSZ anode supports are coated with 8 mol%Y2O3-stabilized ZrO2 (8YSZ) electrolyte and layers of La0.8Sr0.2MnO3-8YSZ/La0.6Sr0.4Fe0.8Co0.2O3 cathode through several coating and sintering processes. The employed stack design methodology enables to stack the cells more easily and to minimize the reduction of power density by assembling the cells into the stack. The stacks are tested for measuring the electrochemical performance at temperatures between 650-750oC with hydrogen fuel. The maximum power density achieved at 750oC is 470mW/cm2, and the voltage degradation rate is 71mV/kh for 1000hours. The stacks are further integrated with a Palladium-Platinum catalysed partial oxidation reformer (CPOx), an afterburner and a heat exchanger to investigate the quick-starting capabilities with hydrocarbon fuels such as propane and butane. After starting the system integrated with the short-stack of four cells, it reached 800oC within 12 minutes. The upscale system with the stack of 54 cells delivered 200W net power output at DC 10 volts.
Fabrication and Electrochemical Characterization of Freeze-Cast Tubular Solid Oxide Fuel Cells
Authors: Du Yanhai , Persky Joshua , Zhao Kai , Ilkhani Hoda , Woodson Theo , Emley Benjamin , Hedayat Nader
Published: February 2020

NASA and others have shown improved power density of planar solid oxide fuel cells (P-SOFCs) fabricated via the freeze casting technique. As a manufacturing process, freeze casting is capable of producing ceramic, metal, and cermet components with unique and tailorable microstructural features that enhance SOFC performance. Low thermo-cyclic durability and slow startup times are common problems for P-SOFCs and have similarly limited the development of freeze cast P-SOFCs. Tubular SOFCs (T-SOFCs) have demonstrated superior thermal cycling capability and relatively fast startup times but have been reported to have lower volumetric power density compared to P-SOFCs. The utilization of freeze casting for fabrication of tubular geometries is suggested as a solution to significantly increase the volumetric power density of T-SOFCs by enhancing gas diffusivity and triple phase boundary reactions and to be at par or better than the power densities of state-of-art P-SOFCs.

This paper reports the fabrication and characterization of freeze cast tubular anode supports for SOFCs. NiO-8YSZ (nickel oxide yttria-stabilized zirconia) anode supports were fabricated using three methods: gelation casting, center pin method, and a freeze and drain method. Slurry rheology was modified for vertical dip coating, and a dual purpose freezing and drying chamber was designed and manufactured. The effects of slurry properties and process parameters were studied with respect to the resulting microstructures. The freeze and drain method was determined to be optimum for producing highly porous tubular anode supports with hierarchical, acicular or dendritic micro-pore channels. With an optimized freeze-drying cycle, drying time was reduced significantly with minimal residual moisture in the green bodies. Additionally, the electrochemical performance of the T-SOFCs with freeze cast anode was evaluated.

Figure 1
Novel SOFC Design with a Co-Sintered and Inert-Supported Cell Concept
Authors: Haeffelin Andreas , Njodzefon Jean-Claude , Matte Eric , Lupetin Piero
Published: February 2020

The demand for energy-efficient, decentralized and environmentally friendly power production is expected to grow in the coming years. Solid oxide fuel cells (SOFC) have received much attention due to their wide range of applications. Cells with different designs (planar and tubular) and supports (electrolyte-, anode- or metal- supported) have been developed and intensively tested in terms of performance, degradation rate and lifetime. Still, technical improvement and especially the cost reduction are crucial factors to make SOFC attractive for the market.

In the framework of a public funded project, a novel SOFC-concept is evaluated that has advantages in terms of costs and lifetime. The cell is mechanically supported by an inert porous silicate layer on the air side and was designed to enable a one-step co-sintering process of the entire cell at temperatures between 1100 °C and 1300 °C (Fig.1). In this contribution, we present the current status of the cell performance in this novel SOFC concept. First investigations carried on co-sintered button cells showed very promising results, namely high OCV values and a power density up to 300 mW/cm² at 750 °C in pure hydrogen.

However, the impedance analysis of the cells points out that a further cathode optimization would be beneficial for the overall cell performance in the novel layout. An additional electrochemical and microstructural analysis of symmetrical cells with a LSM-YSZ cathode sintered on a silicate support showed that cathode properties [1], in particular the oxygen reduction reaction, are strongly influenced by the presence of the silicate during co-sintering, due to evaporation of transition metals from the substrate.

Figure 1
Toward Lower Temperature and More Efficient Solid Oxide Fuel Cell: The Effect of Gibbs Phase Rule on the Triple Phase Boundary
Authors: Reda Mahmoud
Published: February 2020

Stationary SOFCs are source of green electricity to power future electrically powered vehicles. In SOFC the ionic conductivity determines the efficiency. It is obvious that a shift in the operating temperature of solid oxide fuel cells (from 1000 down to around 750–800 degree C) is desired. However, better electrolyte and electrode materials are required for lower temperature operation in order to maintain their high temperature performance. It had been known that both phase purity (single phase) and microstructure of, for example LSGM materials, depend on synthesis procedure and processing and, as a matter of fact, the synthesis of a pure single phase material is rather difficult [1,2].

Two important conclusions are the objective of this research work:

1-The cathode, anode or electrolyte become ionically conducting at a sharp phase transition temperature (the operating T of the SOFC). Below such T the materials loses its ionic conductivity [3]

2-The Gibbs phase rule (single phase and two components of the air) may be applied at the triple phase boundary (TPB) where the number of phases of the MIEC (single or two phases) are in contact with single and pure phase electrolyte [4].

1. Djurado, E. and Labeau, M., J. Europ. Ceram. Soc., 1998, 18, 1397–1404

2. Tas, A. C., Majewski, P. and Aldinger, F.,. J. Am. Ceram. Soc., 2000, 83, 2954–2960

3. S. Hall, Superionics: crystal structures and conduction process,.Rep. Prog Physics, 2004, 67, 1233-1314

4. S. B. Adler, Factors Governing Oxygen Reduction in Solid Oxide Fuel Cell Cathodes, Chem. Rev. 2004, 104, 4791−4843.
Electrochemical Performance and Stability of (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ Cathode Powders Modified by Atomic Layer Deposition
Authors: Torabi Alireza , Geary Timothy C , Barton Joseph , Willman Carl , Ghezel-Ayagh Hossein , Roeder Jeffrey F , Zeberoff Anthony F , Golalikhani Maryam , Van Buskirk Peter C , Huang Kevin
Published: February 2020

For solid oxide fuel cell (SOFC) systems to become economically competitive, continuous development of new materials and processes is required not only to enhance SOFCs durability but also to reduce their cost. The cathode electrode is known to contribute the most to SOFC performance degradation and efficiency loss. In the case of strontium doped lanthanum cobalt iron oxide, it has been frequently suggested that strontium migration to the cathode surface under operating conditions plays an important role in the degradation. Recently, there have been extensive efforts to modify the surface of the cathode in order to improve the reliability. Most of these attempts have been focused on surface modification subsequent to the cell fabrication (e.g. infiltration). An attractive alternative is to modify the cathode powder surface prior to incorporating the powder into the SOFC. This approach would simplify the manufacturing flow, allowing a “drop-in replacement” of existing cathode powders, while potentially providing similar or even better performance enhancements.

In this work, commercial (La0.6Sr0.4)0.95Co0.2Fe0.8O3-
d (LSCF) powders have been modified by atomic layer deposition (ALD) using zirconia-, ceria- and hafnia-based oxides. The effect of coating thickness (number of ALD cycles) and dopant addition have been investigated. Morphology and porosity of sintered samples based on ALD coated powders and the pristine powder were found to be rather similar. On the other hand, the electrochemical performance of cathodes based on the ALD treated powders was significantly different from that of the unmodified cathode. This paper examines the details of electrochemical behavior of ALD modified and unmodified powders. Electrochemical impedance spectroscopy (EIS) analysis of symmetrical cells under air at 600-800 °C temperature range showed that high and medium frequency arcs were highly affected in ALD treated samples whereas the low frequency region stayed unchanged. The effect of surface modification of LSCF powders on durability of the LSCF-based cathode is under comprehensive assessment.
Development and Evaluation of 3-Layer Metal Supported Solid Oxide Fuel Cell Short Stack
Authors: Jang Young-hoon , Lee Sanghun , Shin Hoyong , Bae Joongmyeon
Published: February 2020

A solid oxide fuel cell (SOFC) is promising technology because of its high electrical efficiency and environmental performance. SOFC can utilize solid ceramic electrolyte, so it can avoid the problems like corrosion, leakage and electrolyte management that often occur in liquid electrolyte. However, these ceramic based SOFC has weakness in external impacts because of its brittleness and relatively low strength. For this problem, metal-supported SOFC has been suggested. Metal supported SOFC refers to SOFC which replace its ceramic support to metal support for enhancing mechanical strength. Metal-support SOFC includes higher mechanical strength, better resistance to vibrates and impacts than conventional SOFC. So, metal-supported SOFC can be applied to movable applications like automobile, train and ship as well as stationary power generation system.

 In this study, 3-layer metal-supported SOFC short stack was designed and developed for APU (Auxiliary Power Unit) application. The short stack was composed of metal-supported cells, interconnect plates, ceramic sealant, gasket and metal foams. The metal-supported SOFC cell was fabricated by sinter-joining method and dimension of metal-supported SOFC cell was 120 x 80 mm2 and active cathode area was 110 x 70 mm2. For the material of interconnect plates and metal supports, Crofer 22 APU alloy was used which has high resistance to oxidation, low rate of chrome vaporization and good electrical conductivity of its oxide layer. Also, hybrid sealing system of ceramic sealant and sealing gasket were applied for gas tightness.

 Electrochemical performance of the short stack was evaluated in 800 ℃. The I-V-P characteristics was measured in 1 L/min of hydrogen and 5 L/min of air. Open circuit voltage (OCV) of the short stack was 3.0 V and it showed stable value. The maximum electrical power of the short stack was 23.1 W. In I-V curve, it seems to nearly linear shape which means ohmic resistance governs overpotential of the short stack. This ohmic resistance may originated in current collection from electrodes and it will be further analyzed. Moreover, the short stack was operated for 120 hours in galvanostatic mode with 2.16 A of discharge current. In the beginning, the operation voltage of the short stack was 2 V and there was no rapid initial degradation. Over time, voltage of the short stack was slightly decreased. After 120 hours, voltage of the short stack was 1.81 V and its degradation rate was 9.5 % per 120 hours. This seems to be due to chrome poisoning of cathode and this problem also will be further analyzed.

Figure 1
Study on the Fabrication and Performance of Very Low Pressure Plasma Sprayed Porous Metal Supported Solid Oxide Fuel Cell
Authors: Gao Jiu-Tao , Wang Yue-Peng , Li Cheng-Xin , Zhang Shan-Lin , Yang Guan-Jun , Li Chang-Jiu
Published: February 2020

Solid oxide fuel cell (SOFC) is a high efficiency clean device that directly converts chemical energy of the fuel gas into electric energy. The long-term degradation and stability are the main problems at high temperature, so how to reduce the working temperature becomes a hotspot of research. It is an important way to reduce the thickness of electrolyte. Therefore, how to produce dense and thin electrolyte films economically becomes particularly important. It has been reported that a uniform and dense coating is hopefully prepared by using very low pressure plasma spraying (VLPPS) technology. Due to low operating pressure (~100 Pa), the plasma plume length elongates and its diameter enlarges. Under this condition, the particles can been heated for more time, and it is helpful to form dense coatings. The current study focuses on this technology for application in porous metal supported solid oxide fuel cell (MS-SOFC), especially for preparation in electrolyte. Using SEM, it was found that the densification of the electrolyte was very well, and this could be confirmed by the open-circuit voltage (OCV) of the cell. In the temperature range of 550~750 ℃, the OCV of the cell fairly stabilized between 1.05 V and 1.1 V. The cell was also analyzed by using electrochemical impedance spectroscopy (EIS). The maximum power density of the cell could be up to more than 1200 mW/cm2 at 750 ℃. The long-term stability of the cell was also preliminarily explored, and the result has shown that it is a very promising method for application in MS-SOFC.
Novel Approach to Strengthening Ceramic Cathode Contact and Validation in a Generic Stack Test Fixture
Authors: Chou Yeong-Shyung , Bonnett Jeff F , Stevenson Jeffry W
Published: February 2020

The mechanical integrity of cathode contact during routine thermal cycling plays an important role in the performance of solid oxide fuel cells. This is because the final stack firing is typically a few hundred degrees lower than normal sintering temperatures, which led leads to poor solid-state sintering and hence poor cathode contact strength. To improve the contact strength and thermal cycle stability, precious metal such as silver has been used and showed good thermal cycle stability. However, issues of cost as well as long-term volatility remain unacceptable for practical industrial application. In this work, we examined three approaches to strengthening cathode contact by (1) mechanical interlocking with engineered surface, (2) enhanced sintering with sintering aid CuO and Bi2O3, and (3) reinforcement with strong and inert YSZ short fibers. Density was measured and bulk strength was determined with diametral compression tests. Ceramic bilayer couples were joined at elevated temperatures of 850 and 950oC for 2h with candidate LSM20 contact using the three approaches. Uniaxial tensile strength measurements were conducted on joined couples at room temperature. Fracture surface analysis was applied to correlate with strength results. The results showed the largest improvement in contact strength with both engineered cathode surface and sintering aid of Bi2O3. The effect of YSZ short fibers alone resulted in very poor strength due to sintering with rigid inclusion. The strength contribution was minute when combining both sintering aid and YSZ fibers. Finally, candidate cathode contact compositions will be tested on a 2”x2” LSM-based cell in a generic stack fixture to assess its effect on thermal cycle stability as well as stability at 800oC for 500-1000h. Post-mortem optical and electron microscopy will be conducted to assess the microstructure and chemical compatibility of cathode and contact materials.
A Comparative Study on the Densification Behavior of Yttria-Stabilized Zirconia Electrolyte Powders
Authors: Panthi Dhruba , Hedayat Nader , Du Yanhai
Published: February 2020

Solid oxide fuel cell (SOFC) electrolytes are usually co-sintered with one of the electrodes (support component) at temperatures ≥1400 °C to get a fully densified microstructure. Lowering this temperature to 1200–1300 °C offers several advantages such as prevention of microstructure coarsening of the electrode and undesirable reactions between the electrolyte and electrode materials, lower sintering cost, and shorter production cycle time. To lower the electrolyte sintering temperature, a thorough understanding of the densification behavior of the electrolyte materials is important. In the current work, we compared the densification behavior of three different types of 8 mol% yttria-stabilized zirconia (YSZ) electrolyte powders: (i) TZ-8Y from Tosoh (Japan), (ii) MELox 8Y from MEL Chemicals (UK), and (iii) YSZ-HT from Huatsing Power (China). The YSZ powders were pressed to form disc-shaped pellets that were sintered at different temperatures ranging 1200–1400 °C. The density and linear shrinkage of the sintered pellets were measured. Among the three YSZ powders, MELox 8Y showed the best densification behavior at lower sintering temperatures with 93 and 96% of the theoretical density at 1250 and 1300 °C, respectively. Although YSZ-HT showed higher sintering rate than TZ-8Y, a sintering temperature of 1350 °C was required for both the powders to reach a theoretical density ≥95%. Our results indicate that different factors besides the particle size play a significant role in determining the sintering rate and densification behavior of the YSZ electrolyte. These factors possibly include the powder synthesis method, post-processing of the powder (such as spray drying), and so on.

Figure 1
Development and Test of a Solid Oxide Fuel Cell Subsystem with a Low Temperature Anode Off-Gas Recirculation
Authors: Peters Roland , Engelbracht Maximilian , Tiedemann Wilfried , Hoven Ingo , Deja Robert , Nguyen Van Nhu , Blum Ludger , Stolten Detlef
Published: February 2020

Solid oxide fuel cell systems with an anode off-gas recirculation have the potential for high electrical efficiency. The anode off-gas recirculation within an SOFC system has two significant advantages. Firstly, a part of the unused fuel at the stack outlet is returned to the stack inlet, where it can again participate in the electrochemical reaction. Therefore, the amount of fresh fuel fed into the system can be reduced. This increases the system fuel utilization and leads to a significant increase in efficiency. Secondly, the recirculated electrochemically produced steam can be used for the steam reforming process. Thus, during operation an external steam supply is no longer necessary. A challenge is the high anode off-gas temperature of at least 700°C, which prohibits the use of commercially available blower units.

At Forschungszentrum Jülich GmbH an SOFC subsystem with an anode off-gas recirculation loop was developed and tested using methane as the fuel. The off-gas recirculation loop consists of two heat exchangers in combination with a low temperature blower, which operates at temperatures up to 200°C. With this setup, tests were carried out to study the influence of e.g. recirculation rate and fuel utilization on the system operation behavior and performance. During the tests the system fuel utilization was driven up to 93%. The test results indicate that changes in recirculation rate affect the cell voltage, the amount of excess air for cooling and the electrical efficiency. At constant current density high recirculation rates decrease the cell voltage, but also the amount of excess air. Therefore, high electrical efficiency could be achieved with high system fuel utilization at moderate recirculation rates.
Highly Effective Catalysts Supported on Metal Foams for Reforming Hydrocarbons for SOFCs
Authors: Snytnikov Pavel , Potemkin Dmitry , Hutton Phillip , Bosch Russell , Simonov Pavel , Sobyanin Vladimir
Published: February 2020

The development of highly efficient modular power generation units is of great importance. Solid oxide fuel cells (SOFC) are currently considered as the most efficient devices for the conversion of hydrocarbons, (natural gas, LPG, JP or diesel) into electric power. To provide stable SOFC operation, initial fuel, before feeding to the SOFC anode, should be converted to synthesis gas with high hydrogen content. Catalytic steam, combined steam-dry, partial oxidation or autothermal reforming are the most appropriate reactions for this purpose. The optimum temperature for these reactions is 550 − 900 °C, which falls within the SOFC working temperature range. The development of a catalyst system that can act as a combined catalytic reformer and heat exchanger (to remove or supply heat at the reaction zone) is very promising for efficient power generation. The combined catalytic reformer and heat exchange catalyst should have the following characteristics:

high intrinsic activity with respect to its weight and volume (due to size limitations of the reformer);

coking resistance;

high intrinsic heat conductivity (in order to provide uniform temperature and reaction rate distribution across the reformer);

low pressure drop.

The present report summarizes the results obtained during a systematic study of several new nickel- and rhodium- based catalyst compositions supported on metal foams, their performance, and fundamental principles of the above mentioned reactions for conversion of various common hydrocarbon fuels.

A procedure for deposition of active catalyst components onto metal foams has been developed. It was systematically verified on Ni, Ni-Fe, FeCrAlY-steel foams with porosity from 10 to 70 pores per inch (ppi), obtained from various manufacturers. The catalytic performance of the coated metal foam substrates was studied in a fixed-bed continuous flow reactor. Total feed flow rate (GHSV − gas hourly space velocity) ranged from 3,000 to 30,000 hr-1. The reaction temperature varied from 500 to 800 °C. The catalysts (as-synthesized and used) were characterized by BET, XRD, XPS, TEM, EDX, SEM, TPR and TPD techniques.
Nanoparticle Surface Modification Enhanced Anode Performance in La1.7Sr0.3Fe0.9Ru0.1O4 for Intermediate Temperature Solid Oxide Fuel Cells
Authors: Zhou Jun , Wan Yiheng , Wang Junkai , Zong Zheng , Zhang Zihang , Wu Kai , Cheng Yonghong
Published: February 2020

Solid oxide fuel cells (SOFCs) have drawn remarkable attention in recent years due to their distinctive advantages of high efficiency, fuel variety and low environment pollution. Along the way to designing of new cathode materials for SOFCs, an understanding of the mechanism of oxygen reduction reaction (ORR) plays a key role, especially the interaction between O2 molecule and surface of cathode. The results of the first principles calculations of the atomic and electronic structure of a layered perovskite LaSrCo0.5Feo.5O4-δ used as a cathode material for solid oxide fuel cells (SOFCs) are presented and discussed. The oxygen vacancy formation energies is found to be smaller than LaSrCoO4 and slightly lower than the other perovskite, e.g. (La, Sr)MnO3, which widely used as a cathode because of its excellent catalytic activity. From a detailed analysis of difference electron densities, the presence of oxygen vacancies can induce local charge redistribution. Furthermore, a strong hybridization between Co-Oad and Fe-Oad for molecular adsorption was obtained by analysis of density of states. Our results show how the mixed B-site ions produce the excellent adsorption and conduction performance of LaSrCo0.5Feo.5O4-δ and fully support its potential application in next-generation SOFCs.
A New Double Doped Bismuth Oxide with Stable Ionic Conductivity at Intermediate Temperatures
Authors: Jolley Adam G. , Wachsman Eric D.
Published: February 2020

Pure bismuth oxide exhibits the highest oxygen ion conductivity of any known material from approximately 730°C up to the melting point. While the highly conductive FCC cubic phase of Bi2O3 can be stabilized to room temperature by doping the structure, the conductivity ultimately suffers at intermediate temperatures due to the oxygen subblattice ordering. Traditional bismuth oxide based electrolytes are not suitable in solid oxide fuel cells that operate below approximately 600°C because of the ordering phenomenon. Reported herein is a Bi2O3 electrolyte material that does not order below 600°C. At temperatures that range from 400°C up to 550°C the electrolyte material does not exhibit noticeable degradation of conductivity, even after annealing for hundreds of hours. Although the oxygen ion conductivity of the material is not equivalent to FCC cubic Bi2O3, it maintains superior conductivity to other prominent SOFC electrolytes such as GDC, SNDC, and YSZ. Furthermore the highly conductive and stable bismuth oxide material also works in a composite cathode alongside LSM. This dual bismuth based electrolyte and cathode design allows for a stable performing SOFC that can operate at intermediate temperatures.
Anodic Performance of La0.5Sr0.5Mn0.9Al0.1O3 Perovskite Oxide for Solid Oxide Fuel Cells Using Dry C3H8 Fuel
Authors: Ishihara Tatsumi , Bahrain Audi M. K. , Wu Kuan-Ting
Published: February 2020

Direct utilization of hydrocarbon for Solid Oxide Fuel Cells (SOFCs) using oxide ion conductor have the advantage of cost, high energy conversion efficiency and expanding the application area of SOFC. By eliminating the initial external reforming process of hydrocarbon fuels to syngas, significant advantages in cost and simplicity of gas handling process can be expected. Theoretically, direct utilisation of hydrocarbon for fuel is possible in SOFC using oxide ion conducting electrolyte, however, this is usually not easy when the conventional Ni base metal is used for anode because the formation of carbon is significantly occurred resulting in the deactivation of anode, or in the most serious case, permanent failure of the cell is occurred. Even methane as fuel, thermodynamic calculations predict that carbon will form at 1073 K unless steam is co-fed.

In this study, Co and Al co-doping to La0.5Sr0.5MnO3 (LSM55) for anode were studied and it was found that doping Co is effective for decreasing anodic IR loss and the power density could be much increased by doping Co for Mn site of LSM doped with Al. XRD measurement suggests that Co was substituted Mn site over wide composition range and up to 40 mol%, partial substitution of Co to Mn in LaMnO3 structure was successfully performed. It was found that the maximum power density was increased by doping Co for LSM doped with 10 mol% Al for both H2 and C3H8 fuel. In particular, the smallest IR loss and anodic overpotential were achieved when 20 mol% Co was doped. The maximum power density of the cell using La0.5Sr0.5Mn0.7Al0.1Co0.2O3 was achieved 953 and 246 mW/cm2 for H2 and C3H8 fuel at 1273 and 1173 K, respectively. Increase in power density can be assigned to the increased surface activity to the electrochemical oxidation by doping Co. Although stability of LSM perovskite structure is still insufficient in dry C3H8 atmosphere, doping Al is effective for increasing stability and so co-doping Al and Co to Mn site of LaMnO3 is effective for decreasing anodic overpotential for direct C3H8 type SOFC.

Mixing oxide ion conductor to Co and Al doped LaMnO3 anode was further studied for increasing power density. Among the examined mixed conductor, it was found that mixing Sm doped CeO2 is effective for increasing power density and the MPD of 850 mW/cm2 was achieved at 1173 K on 20 wt% SDC mixed with Co and Al doped LSM anode.
Effect of Gd-Doped Ceria Interlayer Microstructure on the Interdiffusion Behavior Between La0.6Sr0.4Co0.2Fe0.8O3-δ Cathodes and Yttria-Stabilized Zirconia Electrolytes
Authors: De Vero Jeffrey Centeno , Bagarinao Katherine Develos- , Kishimoto Haruo , Ishiyama Tomohiro , Yamaji Katsuhiko , Horita Teruhisa , Yokokawa Harumi
Published: February 2020

Formation of secondary phases at the interface between cathode and electrolyte is one of the issues affecting the long-term stability of solid oxide fuel cells. La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) perovskite cathode is known to react with yttria-stabilized zirconia (YSZ) forming SrZrO3 at the interface. To reduce secondary phase formation, a reaction barrier layer such as Gd-doped ceria (GDC) is inserted between LSCF and YSZ. However, the stability of the reaction barrier layer after long-term operation may be directly affected by the microstructure and cation diffusion through GDC. In this work, the microstructure of the reaction barrier layer is controlled by growing the GDC thin films on polycrystalline and single crystal YSZ (100) electrolytes using pulsed laser deposition technique. Electrochemical impedance spectroscopy (EIS) and microstructural analyses were performed on LSCF|GDC|YSZ|Pt cells with different GDC interlayers under an open-circuit condition at 800⁰C for 300 h in air. It is observed that SrZrO3 formed primarily at the LSCF/GDC interface of cells with polycrystalline GDC interlayers resulting to a rapid increase in area-specific resistance (ASR) with time. In the case of single-crystalline GDC interlayer, no apparent formation of SrZrO3 but a possible formation of GdFeO3 or LaMO3 (M= Co, Fe) at the LSCF/GDC interface was observed. EIS analysis of cells with single-crystalline GDC interlayer reveals a slow increase in the ASR with time. Microstructural evolution of the interfaces and type of secondary phase formation at the interface gives rise to a different rate of ASR and is shown to be directly related to the microstructure of GDC interlayers.
Thermodynamic Stability of La0.6Sr0.4Co0.2Fe0.8O3-
δ in Carbon Dioxide Impurity: A Comprehensive Experimental and Computational Assessment
Authors: Darvish Shadi , Zhong Yu , Gopalan Srikanth
Published: February 2020

Solid oxide fuel cells (SOFCs) operate on a variety of environments and are exposed to a variety of environmental impurities. One ubiquitous impurity in the cathode gas is carbon dioxide whose concentrations are usually upwards of 400 ppm depending on the source of the air and leaks through pinholes across the electrolyte. In this work we present a comprehensive thermodynamic assessment of the phase equilibria La0.6Sr0.4Co0.2Fe0.8O3-
δ (LSCF) – CO2 – O2 system using a molten salt method and using CALPHAD (Calculation of Phase Diagrams). Detailed thermodynamic maps of LSCF in carbon dioxide environments are provided under operando conditions and compared with available experimental data. We also examine contradictions between experimental data and computation of phase equilibria, and attempt to reconcile them by paying close attention to differences in cell operating conditions. Finally we discuss future directions where the combination of experimental and CALPHAD assessment of the thermodynamics of fuel cell component materials can be used to provide design guidance.
SOC Development at Forschungszentrum Jülich
Authors: Blum Ludger , Fang Qingping , de Haart L.G.J. , Malzbender Jürgen , Margaritis Nikolaos , Menzler Norbert H. , Peters Roland
Published: February 2020

In order to become a substantial part of the energy supply infrastructure in the course of the German “Energiewende” (energy system transition), SOFC plants in the power range of 100 kW or larger must be realized. Scale up of units will become even more important in the field of electrolysis to balance electricity conversion and consumption. Therefore, currently one of the main goals of SOC development at the Forschungszentrum Jülich is the development of single stacks in the 15 kW power range as a basis for development of larger units. The core structural feature is a planar-type window frame stack-design, which allows the integration of standard-sized cells, e.g., 10 ×10 cm², in a 2 × 2 array. Based on this design, the 15 kW stack will consist of six sub-stacks, each having 20 planes. Initial operational results with such a sub-stack are reported. Aiming towards stationary applications, long term behaviour is of great importance. The 'world-record' short stack is now in operation under load for more than 80,000 hours, showing an average voltage degradation rate of 0.6%/kh, which decreased to less than 0.3%/kh in the last 30,000 hours. Next to long term stability, electrical net efficiency plays an important role. A net efficiency of 57% could be demonstrated with a 5 kW system operated with methane at 93% fuel utilization using low temperature anode off-gas recirculation. For stationary applications, a concept was developed and proven that allows safe system operation without additional forming gas.

In the case of mobile applications such as range extenders or APUs in trucks, the dynamic behaviour is of greater importance. Therefore, the Jülich lightweight cassette design has been advanced with the potential of improved thermomechanical properties using glass sealing instead of metal soldering to integrate the cells into the cassette frame.

Growing emphasis is placed on the development of high temperature electrolysers (SOEC). Currently, a standard two-layer short stack is in operation for more than 18,000 hours in electrolysis mode at a current density of -0.5 A.cm-², showing a voltage degradation of less than 1%/kh. Since in the field of energy storage and electricity production based on renewable energy, the reversible operation of such systems is of great interest, the concept of a 5 kW r(eversible)SOC plant has been devised and is now under construction. A 5 kW stack in a system configuration, representing the fuel cell part of the rSOC system, was operated successfully with a hydrogen utilization of 80%.