1. Group 14 Rifat Mumith Jenny Nacu Napat Napattaloong Bryan O’Bannon
Oxide Scale Formation on Different Metallic Interconnects For Solid Oxide Fuel Cells: Renewable Energies and Materials Approach
Group 14
Rifat Mumith
Jenny Nacu
Napat Napattaloong
Bryan O’Bannon
Figure 1:
A diagram showing each component of a solid oxide fuel cell.
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2. Introduction to SOFC (Solid Oxide Fuel Cells)
Alternative technology towards energy sources are constantly under research
Fuel cells are a common technology that provides electrical power from chemical fuels such as hydrogen and hydrocarbons
Basic chemical reaction in a fuel cell
The hydrogen ions are drawn through the electrolyte after the reaction. At the same time, electrons are drawn from the anode to the cathode through an external circuit, producing direct current electricity
As seen, one of the many advantages of fuel cells is its ability to generate electricity with little pollution
A fuel cell’s reaction with hydrogen and oxygen creates a completely harmless byproduct - water
The primary focus of SOFC research deals with a specific type of fuel cell: Solid oxide

3. SOFC (Solid Oxide Fuel Cells)
SOFC uses ceramic compound of metal oxides as electrolyte
Essentially, the fuel cell contains two electrodes, one positively charged (cathode) and one negatively charged (anode)
The reaction taking place in a fuel cell occurs at these electrodes
Anode Reactions:
2H2 + 2O2- »» 2H2O + 4e-
2CO + O2- »» 2CO2 + 4e-
SOFCs efficiency reaches 60 percent
Operating temperatures are about 1,000 °C (about 1,800 °F)
At such high temperatures, waste heat can be recycled to generate additional temperature
However, the high temperature limits SOFC units and researchers are aiming to limit their working temperatures
Cathode Reaction:
O2 + 4e- »» 2O2-
Schematic diagram of a solid oxide fuel cell showing how chemical energy is directly converted into electrical energy.
Thus, for the future of SOFC, current operating temperatures calls for changes

4. The Search for Interconnect Materials
Reducing operating temperature allows less expensive metallic materials to be used for interconnects
Interconnect materials connect the anode side to the cathode side of an adjacent cell
They act as a barrier to prevent contact between the reducing and oxidizing atmospheres
Recently, metallic materials are being considered to replace ceramics in SOFC
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Metallic interconnects are easier to fabricate and cost less than ceramics, but their lifetime under SOFC need improvement

5. The Search for Interconnect Materials
Thermal expansion is the tendency of a material to change in shape, area, or volume in response to change in temperature, where its general volumetric thermal expansion coefficient is given by
Ideal interconnect materials should exhibit the following properties:
Good conductivity, the degree to which a specified material conducts electricity
Where ρ is defined as a material’s electrical resistivity
R: electrical resistance in ohms Ω
L: length of material (m)
A: cross sectional area of specimen (m2)
Conductivity, σ . is defined as the inverse of resistivity
Chemical and thermal stability at operating temperatures at around 800 C
Its thermal expansion coefficient (TEC) between ambient and operating temperatures should be comparable to those of the electrode and electrolyte
No reaction or inter-diffusion between interconnect and its adjoining components
A low permeability to reactant gases, good mechanical strength and corrosion resistance
Easy to manufacture and not costly
Figure displaying deformation under increased temperature and pressure
Greater deformation of conductive particles lead to larger contact area

6. The Search for Interconnect Materials
Oxide layer formation
Example material: Crofer 22 APU
A high- temperature ferritic stainless steel especially developed for application in SOFC
At high temperatures (up to 900 °C) a chromium manganese oxide layer is formed on the surface of Crofer 22 APU
Thermodynamically stable
Possesses high electrical conductivity
Low coefficient of thermal expansion that is matched to that of ceramics typically used in fuel cells
The different elemental compositions involved in Crofer 22 APU contributing to its properties

7. Crofer 22 APU: Relating to Materials
Typical properties at room and elevated temperatures
Crofer 22 APU is characterized by excellent corrosion resistance at high temperatures in anode and cathode gas
Oxide layer provides good conductivity
Ease of working and processing
Stress- Srain curves at varying temperatures
Crofer 22 APU: Relating to Materials

8. Crofer 22 APU: A closer look at its micro-scale properties
Stainless steels are used due to their resistance to oxidation
Recalling, Crofer 22 APU is a ferritic stainless steel (FSS), a type most attractive for metallic interconnects for their favorable strength at high temperatures, machinability, closely matched TEC with electrodes, and low manufacturing cost
Looking closely, FSS have a body-centered cubic structure, consisting of iron- chromium alloys
Structure the same as pure iron at room temperature
Main alloying element is chromium
At all temperatures, commercial FSS have a BCC structure at all temperatures
Temperature does not induce phase change in solid state
The oxidation resistance of FSS increases with increasing Cr content in FSS
Their structure can be easily deformed and machined
Photo taken from

9. Example of rust formation
The Reason for Metallic Interconnects Research and Development: Oxide scale formation
Metallic interconnects have two main disadvantages:
Release of volatile chromium species and the precipitation of chromia, blocking the cathode/ electrolyte interface, where the reduction of the oxidant occurs
Chromia hinders reduction of oxygen necessary for SOFC operation
In addition, large growth of oxide scales leads to accelerated corrosion, affecting the stability of the metallic interconnects
Corrosion in metals is a common natural process
Such electrochemical oxidation results in the reaction with an oxidant (i.e. oxygen or sulfur)
Rusting is a popular example where the formation of iron oxides damages the material by producing oxides or salts of the metal
Example of rust formation
Result of corrosion of a metallic iron. Iron is oxidized at an anodic side on the surface of the iron, which is often an impurity or a lattice defect
Oxygen is then reduced to water at a different place on the iron, acting as the cathode. Electrons are then transferred from the anode to the cathode.
Water is a solvent for the iron that will act as a salt bridge. Rust is subsequently formed by the oxidation of iron by the atmospheric oxygen

10. The Reason for Metallic Interconnects Research and Development: Oxide scale formation
As seen, oxide scale formation in metals used for SOFC is one of the most important consideration regarding metallic interconnect choices
Degradation disrupts the useful properties of materials and structures
Thus, researchers are testing different materials using several approaches to observe oxide formation
Evidently, SOFC works more efficiently by having a metallic interconnect that is most resistant to corrosion
Fig 2
Micrograph (Fig 2) showing metal corrosion crust interface of metal sample (Fig 1)
Where there the white in the image is the metal, the grey as the corrosion products, and in black the resin
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Fig 1

11. Summary of Main Research: Oxide scale formation on different metallic interconnects for solid oxide fuel cells
The quality of SOFC are constantly being improved with new research being conducted constantly.
The interconnects of SOFC typically build oxide scales from the high temperature and oxidation as shown in the animation to the right.
Research is looking for the best materials to use to increase the resistivity of the oxide scale buildup.
Materials such as FSS have shown to be excellent candidates for metallic interconnects.
Different FSS materials however have shown to perform better under the operating conditions of the SOFC.
Thinner oxide scales and a high resistance to oxidation was found for the steels with higher chromium content and reactive elements.
The geometry of the crystals in the interconnects played a significant role in the conductivity of the oxide scales.
To improve research in this paper, we recommend that the researchers focus on varying the amount of chromium in the FSS materials to see if conductivity improves even more.
Research in the future should include tubular solid oxide fuel cells to see if oxide scale formation is affected by change of shape.

12. Simplified rendition of a fuel cell power plant.
Article #1
To gain a better understanding of the degradation in materials, we consider the following research result study:
DEGRADATION OF SOLID OXIDE FUEL CELL METALLIC INTERCONNECTS IN FUELS CONTAINING SULFUR M. Ziomek-Moroz and J. A. Hawk U.S. Department of Energy, Albany Research Center
The U.S. Department of Energy considers SOFC as one of the most promising fuel cells
Fuel cells are not just for industry power plants, but on people’s homes
As mentioned, their interest in fuel cell applications are driven primarily by their potential for high efficiency and very low environmental impact
Their research provides insight on the material performance of nickel, ferritic steels, and nickel- based alloys in fuels containing sulfur, primarily, H2S
They seek to quantify the extent of possible degradation due to sulfur in the gas stream
Simplified rendition of a fuel cell power plant.

13. Degradation of SOFC metallic interconnects
Degradation of SOFC metallic interconnects
Approach:
Albany Research Center has focused on developing high temperature materials that can be used in a SOFC system
Performance characteristics of metallic alloys must be investigated in simulated SOFC environments, as well as environments containing sulfur
Data exposure studies have been performed on alloys in air and in an air- H2 environment
Tubular approach- allows alloy sample exposure during one experimental run (the tubes will consist of a series of alloys welded together to create a tube on the appropriate length
Upon running the tubes, different environments can be performed, one with air passing through the tube, one with H2, and one with with H2-H2S mixture
The tube will then be placed in a furnace set up
Findings:
Scales formed on Fe-Cr steels in H2-H2S mixtures exhibit less adherence to the substrate, and can be porous and cracked
Chromic scales consists of at least two layers, with sulfides of the steel alloying additions occurring at the inner layer adjacent to material
The higher the concentration of H2S, the higher the corrosion rate
Sulfur corrosion rate of Fr-Cr alloys as a function of alloy composition and H2S concentration

14. Continuation of degradation of SOFC metallic interconnects in fuels containing sulfur
At high temperatures, corrosion rate decay can be observed
The figure shows that Cr and Ni content affect the overall corrosion rate
The three types of steel observed displayed a non-uniform character under the experiment
Through their research, it is found that the types and levels of impurities in fuel streams for SOFC operations depend on the natural source of the fuel
SOFC operations also depend on the manner in which hydrogen production occurs
Sulfur is one of the major impurities found in natural gas that is intentionally added as a safety precaution
However H2S may occur, a presence that reduces SOFC cell performance, and as seen, makes metallic based materials susceptible to sulfur corrosion
Quantifying material wastage:
where D is the original diameter of the tube before exposure, Di is the diameter of structurally intact alloy after exposure, and N is the number of measurements on the test sample
Sulfur corrosion rate of alloyed steels as a function of temperature in an H2-H2S environment: 1) 18-8 Cr-Ni austenitic steel; 2) ferritic steel with 7 to 16% Cr; 3) steel with 3% Cr

15. Concluding degradation of SOFC metallic interconnects research
Relating to original material discussed, Crofer 22 APU;
SEM images of cross sections and the element distribution profiles of the chromia-forming alloys after oxidation treatment at 900°C in air for 500 h
The U.S. Department of Energy recognizes the critical use for this type of energy alternative. It aims to progress their research to provide a clearer picture of how iron and nickel- base alloys perform in SOFC environments
Essentially, their hope is that their studies will lead to strategic decisions for material selection for SOFC metallic interconnects by understanding the complex interaction of materials and environment, as well as surface modification strategies to develop operations for lowering cost of alloys
The knowledge gained can be used to better select alloys for BOP applications in heat exchangers, recuperators, fuel processors, de-sulfurization units, pipes and tubes, and other ancillary equipment

16. Summarizing Introductory Research
Solid Oxide Fuel Cells are widely known for their capabilities as an alternative energy in today’s society
Thus, researchers as well as the U.S. Department of Energy, are devoting time to search for the ideal metallic interconnect for SOFC
An important consideration for their search includes observing the effects of oxide scale formation. Such formations results in corrosion and hinders cell performance
Thus, it is important to find the best metal that displays properties that are most resistant to the high heat operations of SOFC
The upcoming slides will explain a more detailed approach to the different research through oxide scale
Upon considering and comparing different materials regarding its state upon oxidation, researcher can decide the most ideal metal for SOFC
Table displaying the different phases found in different metals investigated in main research

17. Article #2: Evaluation of Solid Oxide Fuel Cell Interconnect Coatings: Reaction Layer Microstructure, Chemistry and Formation Mechanisms
This article discusses improvements to electrolyte materials leading to solid oxide fuel cells that can operate at lower temperatures ( ⁰C).
This allows the use of chromia forming metallic interconnects which cost less than ceramics.
Chromia is a poor oxidation resistor and allows the opportunity for the evolution of volatile chromia species.
A protective conductive ceramic coating is necessary to keep from poisoning the solid oxide fuel cell cathodes.
Studies were done to compare Mn1.5Co1.5O4 (MCO) coated and uncoated Crofer 22 APU and Haynes 230 alloys.
Solid oxide fuel cells are very efficient at converting a number of fuels, such as methane and hydrogen, into electrical energy.
A target cost of $400/ KW-1h-1 and each stack must have a minimum lifetime of 40,000 hours.
Solid oxide fuel cells contain no moving parts.
After the hydrogen and oxygen molecules react to form water vapor in the electrolyte, the electrons are pulled from the stack in the form of electricity.
Display of the transport processes through an solid oxide fuel cell interconnect oxide scale and coating.

18. Article #2: Solid Oxide Fuel Cell Interconnect Alloy Requirements
In the past, solid oxide fuel cells were being ran around temperatures of 1000⁰C meaning all components had to be made out of ceramic materials, which could get expensive.
Decreasing the operating temperature range to ⁰C, the traditional LaCrCO3 interconnect can be replaced with less expensive metallic interconnects.
The following are the top eight requirements for a successful and durable interconnect material:
Gas tightness to prevent mixing of fuel and air.
Oxidation and corrosion resistance, stable in air, fuel, water vapor and carbon containing environments.
High electrical conductivity of both the alloy and any oxidation products formed on the alloy during operation.
Thermal expansion coefficient match to the other fuel cell components, generally 10-13x10-6 K -1.
High thermal conductivity to enable a uniform stack temperature.
Mechanical strength and durability at operating temperatures.
Low cost to meet the requirements of $400 kW-1hr-1.
Chemical compatibility with other cell components.
A graph of areas specific resistance measurements at 800ºC of stainless steel 441 with and without a protective coating.

19. Article #2: Coating of Solid Oxide Fuel Cell Interconnects
Sudden poisoning of solid oxide fuel cells occur between triple phases of air, electrolytes, and cathode materials in the presence of CrO3 and CrO2(OH)2.
Areas specific resistance (ASR) are reduced using coating of alloys that may oxide under operation conditions.
It is important that coating does not sufficient limit the electrical conductivity of the interconnects since that is how power is pulled from the cells.
Short circuits during the diffusion of oxygen is possible if zero open porosity is not maintained during coating.
It is difficult to predict the lifespan of the interconnects as it is unreasonable to run a 40,000 hour (about 4.5 years) long test.
Different methods have been used to simulate the wear-and-tear of this length of time by increasing the operating conditions above recommendations.
Some studies have used oxidation kinetics in efforts to predict the lifetime of SOFCs.
Spinel oxide coatings, perovskite coatings, and reactive element oxide coatings are the three main interconnect coatings.
A coated metal foil. Xc and Xf are coating thickness and oxide scale thickness, respectively.

20. Article #2: Methods of Coating Applications
Magnetron sputtering is a physical vapor deposition technique that involves using a vacuum chamber and a magnetic field.
Argon gas is bled into the vacuum chamber, and the plasma is generated by applying an electron field where the argon ions collide with the material giving off a vapor used for coating. Better with pure metals.
Electroplating uses an electrolyte solution and a DC current to oxidize the anode causing positive metal ions to coat the cathode.
This process is the most common because it is simple, inexpensive, and has had great success.
Metal-organic chemical vapor deposition (MOCVD) uses a metal alkyl or hydride precursor that are heated to the vapor phase and introduced to the SOFC interconnects in a cold wall reactor.
This process is commonly used to prepare thin, homogeneous coatings to compound semiconductors.
Slurry coating process is a multi-step process that uses chemically homogenous ceramic powder and glycine-nitrate to apply a coating by painting, spraying, dipping, or screen-printing to a interconnect surface.
This process is low cost and highly manufacturable.
A diagram of the magnetron sputtering process.

21. Article #2: Recommendations
Additional experiment on MCO coating systems need to be ran either at much longer times or at elevated temperatures (>800°C) in order to better understand how reaction layers form and what its equilibrium composition.
Synthesizing chemistries similar in composition to the reaction layers and performing bulk 4-point electrical conductivity measurements would allow for chemistry close to the reaction layers that form on Crofer 22 APU and H230.
Model coating systems must be used to improve diffusive fluxes and rates of reaction layer formation since they are critical to predicting the lifetime performance properties for solid oxide fuel cells. In order to do this, on substrates of interest.
Area specific resistance (ASR) allow reaction layers to be studied under real solid oxide fuel cell operating conditions. This method of testing uses electrical current to help understand how reaction layers form.
Exposing the interconnects to temperatures above the actual use temperature, correlating reaction layer chemistry, and thickness to determine how one might develop an accelerated test.
A diagram of the MOCVD apparatus.

22. Article #2: Summary
Studied efforts to lower operating conditions of solid oxide fuel cells such as lowering temperatures ( ⁰C).
Developed methods to use more metallic interconnects compared to that of ceramic interconnects.
Determined the top eight requirements for a successful and durable interconnect material.
A protective conductive ceramic coating is necessary to keep from poisoning the solid oxide fuel cell cathodes.
Areas specific resistance (ASR) are reduced using coating of alloys that may oxide under operation conditions.
Spinel oxide coatings, perovskite coatings, and reactive element oxide coatings are the three main interconnect coatings.
A target cost of $400/ KW-1h-1 and each stack must have a minimum lifetime of 40,000 hours.
Magnetron sputtering, electroplating, metal-organic chemical vapor deposition (MOCVD), and slurry coating process are the four methods for coating.
Developed a list of recommendations to improve solid oxide fuel cell production and lifetime of product.
A diagram of a solid oxide fuel cell.
A diagram of a solid oxide fuel cell.

23. Article #2: Related to CHEN 313
Went into detail on how the anodes, cathodes, and electrolytes interact with each other in a solid oxide fuel cell.
A number of test reports were find in the article showing the usefulness of certain semiconductors compared to that of ceramics.
It describe how oxidation occurs inside the solid oxide fuel cells and the importance of being able to control that oxidation in order to maximize the lifetime of the solid oxide fuel cell.
How the electrons flowed across the solid oxide fuel cells were discussed and explained how energy was then created to power the interconnect.
A picture of the cathode, electrolyte, and anode layers in a SOFC.
A diagram showing the transfer of electrons in a SOFC.

24. Article #3: Interconnect materials for next-generation solid oxide fuel cells
This article discusses using special coatings on the metallic interconnects to reduce oxide scale formation on metallic interconnects in SOFC
Unlike the main article, the purpose of this article is to compare the corrosion resistance of uncoated and coated of metallic interconnects.
The study uses different types of Ferritic Stainless Steel (FSS) as the material for the interconnect.
The figure to the right shows the visual difference between an uncoated sheet of FSS and a coated interconnect of FSS.
The samples of FSS used were Crofer22APU, AL453, Haynes230, Fe30Cr, and FSS 430
They were either cut in 1x1 cm squares with ~2 mm thickness or cut in 1 cm diameter discs with ~1 mm thickness.
The coatings used in the study were metal organic chemical vapor deposition (MO-CVD) and large area filtered arc deposition (LAFAD).
The coating shown in the figure is a ~1-4 µm thick LAFAD coating which is composed of titanium, chromium, aluminum, yttrium, and oxygen.
The coating was applied in a similar fashion to all the sheets.

25. Area-specific resistance measurements
One of the major criteria that was used to compare the uncoated and coated FSS materials was the area-specific resistance (ASR).
The ASR parameter reflects the resistance, the thickness, as well as the electrical properties of the oxide layers. Lower ASR means better conductivity.
The resistivity of the alloy substrate is negligible compared to that of the oxide scales formed.
The equation to calculate ASR is shown in the bottom figure.
The uncoated and coated samples were oxidised in 800°C laboratory air at atmospheric pressure for 100 hours.
The top figure shows the comparison of uncoated and coated FSS materials.
Each FSS material had a significant decrease in ASR with at least one type of coating which shows that the coating material in several cases increased the electrical conductivity of the oxide scales that formed after 100 hours.
While there were several coated sample that had low ASR measurements, the uncoated materials all had an ASR measured less than 0.1. This measurement shows the FSS materials are also decent candidates for interconnects by themselves.
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26. (Δm/A)2 = Kpt Oxidation Kinetics
During the oxidation exposure, the FSS samples were continuously weighed in a thermobalance in order to acquire oxidation kinetics.
Oxidation kinetics helps to determine the rate of oxide scale growth.
Parabolic rate law constant Kp can be determined from the equation below. (Δm/A)2 is the mass gain of the material over the total oxidised area.
The figure shows the different Kp values for each material under different coating conditions.
All the uncoated materials except for Haynes 230 had a large Kp which means that significant oxide scale formation occurs.
In general, each material had at least one coating in which the Kp was below 1e-14 g2cm-4s-1.
These measurements clearly show how added coatings can significantly reduce the formation of oxide scales on these materials.
Haynes 230 is the only outlier which shows that the material does not necessarily need a coating to perform well in a SOFC.
(Δm/A)2 = Kpt

27. Comparing Kp results with the main article.
The value of the parabolic rate constant can be determined by using the slope of a plot of time vs. weight loss for metallic interconnects.
Similar to article #3, the tables from the main article show that Crofer 22 APU and SS430 follow the rate parabolic constant.
Crofer 22 APU seems to deviate from the constant since its correlation value R is less than the R value for SS430.
Nonetheless, in both cases the trend is clearly there.
Article #3 did not evaluate the Kp value for SS430; however it did calculate the Kp value of Crofer 22 APU.
The two Kp values from the articles are significantly different for uncoated samples of Crofer 22 APU.
The Kp from the main article can be seen in the table below as 7.51e-10 while the Kp from article #3 is approximately 4.89e-14.
The reason for this significant difference may be from the testing conditions that the different studies completed.
It is problematic that both articles got different values, as there may be some error in the research.

28. Materials used for interconnects
The materials used in article #3 were Crofer22 APU, AL453, Haynes 230, Fe30Cr, and FSS 430.
As shown in the table, all the materials except for Haynes 230 consist mostly of Iron.
In addition, the Chromium content of all the materials is the second largest component of each material.
Haynes 230 is mostly Nickel, which explains its unique behaviors under the parabolic rate law measurements.
The materials for the interconnects clearly effect the formation of oxide scales and electrical conductivity.
Some of the materials cannot handle the SOFC operating conditions due to their crystal structure and other features of the chemical composition.
As the articles show, it can be determined that the more chromium in a material, the better it will perform in the SOFC operating conditions.
However, research should be done to determine the chromium threshold in which the materials do not perform as well under the high temperatures.

29. X-Ray Diffraction analysis
The room temperature X-ray diffraction (XRD) patterns of the samples) oxidised at 800 °C for 100 and 1000 hours in air are shown in the figure to the right.
The XRD analysis clearly shows the development of oxide scale in an analytical way.
The figure displays the XRD at 0, 100, and 1000 hours to show the progression of new components on the material.
At time 0, the alloy is all that shows up on the XRD.
As time progresses, several types of oxide scales form.
The quantitative analysis shows that after 100 h the oxide scale of Crofer 22 APU consisted primarily of chromia and the rhombohedral hematite phase, with smaller amounts of spinel, TiO0.89 and Fe3O4.
After 1000 h, the proportion of spinel in SS430 increased but not the proportion of chromia and Fe3O4.The content of (Fe, Cr, Ni)Co2O4 (30.40%) increased considerably, and a small amount of a new hexagonal phase, Co3W (6%), appeared.

30. Effects of MO-CVD coating on material
For uncoated materials, Haynes 230 alloy displays the best behaviour compared to ferritic alloys as shown in the figure B on the right.
For the uncoated Fe30Cr and AL453, the kp values after 100 h at 800 C in air are high; as a matter of fact, these alloys cannot be used as interconnects without a coating as shown on Figure A and C.
In the case of ferritic alloys, the values of the parabolic rate law constants of the coated samples are lower than that of the uncoated specimens.
It is interesting to note that, in contrast to AL453 alloy, in the case of Fe30Cr and Crofer22APU alloys, the coating effect does not depend on the nature of the reactive element; the kp values are equally decreased.
In the case of Haynes230, the effect of coating is not clearly visible; the values of the parabolic rate law constants of the uncoated and coated samples are close to each other.
The study of electrical properties (Fig. 4) of the oxide scales formed on uncoated Crofer22APU, AL453, Fe30Cr and Haynes230 showed that they were well adapted for use as interconnect.
As expected in the case of AL453, the yttrium oxide increased the electrical resistivity of the scale compared to the uncoated alloy

31. Effects of LAFAD coating on material
The LAFAD coating were shown to have the most impressive results among all the coatings tested.
The LAFAD coating contain combinations of diffusion barrier components and conductive components, which give the material qualities that will increase conductivity and reduce oxide scale formation.
However, the LAFAD coating was only tested on FSS 430, a material that does not perform as well in uncoated conditions compared to some of the other materials.
The figure to the right visually shows the effects of adding the coated layer to FSS 430 by using a scanning electron microscope (SEM).
The coating demonstrated excellent thermal stability, low ASR, and negligible Cr volatility.
As the figure shows, the coating retains its thickness after 1500 hours at 800°C with only slight deformation after the extended period of time.
Further research should be done to determine how LAFAD coating will affect materials more suitable for SOFC interconnects.

32. Summary of article #3
Highly -efficient solid oxide fuel cell systems are gaining increased attention for future renewable resources.
Similar to the main article, this article looks into methods to decrease the electrical resistance created from oxide scale formation.
The two methods the research is studying are LAFAD and MOCVD coatings.
The research finds that the coating decreases the ASR as shown in the diagram.
The ASR for the two coatings remained under .01 Ω*cm2, which is excellent for times over 100 hours.
However, the research finds that different coatings work better for different types of materials.
Future research should look into the relationships of coatings and materials for improved results.
To improve this research, we would recommend looking into large scale cost analysis for the utilization of coating on SOFC.

33. Article #4: A novel two-part interconnector for solid oxide fuel cells
This figure illustrates a conventional metallic interconnector
Two common types of interconnectors are: metallic alloys and conducting ceramics.
Metallic alloys are usually preferred due to higher electrical conductivity and easy manufacturing but:
Many metallic alloys can react with the sealant and the electrode materials to produce secondary compounds.
These secondary compounds usually have higher thermal expansion coefficients than the starting material.
The mismatch in thermal expansion can lead to pore and crack formations which lead to fuel leakage.
Ceramics usually has good chemical compatibility with the sealant and electrode materials but:
Ceramics have low electrical conductivity
Ceramics are mechanically weak
Ceramics are difficult and expensive to produce
This article proposes a novel two-part ceramic-metallic interconnector that combines advantages of both ceramic and metallic interconnectors

34. The two-part interconnector
The interconnector includes:
A metallic core which:
Houses the membrane electrode assembly
Made with Crofer 22 APU
A supporting ceramic plate:
Seals and support the metallic core
Distribute fuel and air to the cell
Made with 3YSZ containing 5%wt Al2O3
The interconnector is a part of the short stack for SOFCs, which include from out to in, stainless steel frame, ceramic plate, metallic core, sealant, and a porous Ni mesh.
The Ni mesh was used to enhance current collection and provide a better fuel distribution.
An example of the metallic core and ceramic support plate is shown. The groove on the ceramic plate allows the metallic core to fit perfectly on it.

35. The ceramic support plate
The ceramic plate is made mainly of 3YSZ and small amounts of Al2O3.
The plate has:
a grooved section to house the metallic core.
Two circular holes to inlet and outlet for fuel and air.
The two holes were made to have different sizes to create pressure difference in the flow chamber
3YSZ was chosen because of its mechanical strength and its thermal expansion coefficient close to the electrolyte material and the metallic core.
Sintered bodies with 3YSZ shows a fine crystal grain structure, resulting in improvement in strength, fracture toughness, and resistance to wear and aging.
Adding Al2O3 reduces the cost of the ceramic plate and lower the sintering temperature
Steps on how to create the ceramic support plate is shown. Many steps are required to complete the functioning ceramic plate that will not crack and break during usage.

36. Testing the two-part interconnector
The thermal expansion coefficient of the ceramic plate must be as close as possible to those of the crofer metallic core and 8YSZ electrolyte material
Al2O3 powder was added to 3YSZ in %wt of 0, 2.5, 5, and 10
labeled as CSP-0, CSP-2.5, CSP-5, and CSP-10, respectively.
The test station involves a temperature controlled furnace, an electronic load, the short stack, a computer and hydrogen and nitrogen tanks.
After assembly, the short stack was heated to 500 °C for binder burnout process and ramped to 860 °C for the sealing process. The performance tests were then performed at 750 °C.

37. Testing the two-part interconnector
Results show that the CSP-5 composition is most compatible with the electrolyte and the metallic core.
The addition of Al2O3 lowers the expansion coefficient closer to the electrolytes.
But addition of more than 10% lowers the coefficient to lower than the electrolytes.
CSP-5 has a coefficient between the metallic core and the electrolyte to minimize thermal stress.

38. Comparing the two-part interconnector with the metallic interconnector
Comparing the stack performance of two-part interconnectors with traditional metallic interconnectors shows that, at 750 C:
The two-part interconnector (- - -) has a slightly better performance than the metallic ( ) interconnector
This performance could be because the two-part interconnector has a better fuel and air distribution from the two different sized holes in the ceramic plate.

39. Comparing the two-part interconnector with the metallic interconnector
The metallic interconnector shows formation of cracks even in small temperature gradients.
The cracks seen below form as the result of the formation of secondary compounds during operation.
The secondary compounds have a higher thermal expansion coefficient than the metallic interconnector and the electrolytes
The figure below displays cracks in the sealing region of the metallic interconnector
Resulting metallic interconnector image courtesy of

40. Comparing the two-part interconnector with the metallic interconnector
The two-part interconnector does not form any secondary compounds that have higher thermal expansion coefficient than the metallic core or the electrolytes.
To make sure the ceramic plate had a thermal expansion coefficient in the region between those of the metallic core and the electrolytes, 5%wt of Al2O3 was mixed in with the ceramic.
The two-part interconnector showed no cracks or pores in the sealing region after short stack tests as seen in Figure 9b.
The Figure shows that the sealing region contains no signs of degradation, i.e. cracks or pores, from secondary materials having higher thermal expansion than the core and the electrolytes.

41. Pros and Cons of the two-part interconnector
Pros
Have similar performances to the conventional metallic interconnector
Slightly better due to the better fuel and air distribution
Provides better sealing of SOFC stacks
The two-part interconnector does not form secondary materials
Eliminates formation of cracks or pores that can threaten the structural integrity of the SOFC stack.
Manufacturing cost is reduced due to addition of Al2O3 into the 3YSZ.
Cons
The ceramic plate is challenging to manufacture due to the geometry of the plate
A three-step sintering procedure must be followed to produce and dense and crack free plate.
More studies needed for multiple cell stacks
Conventional metallic interconnector

42. Summary of Article #4
A novel two-part interconnector is introduced to solve the sealing problems in conventional metallic SOFC.
The two-part interconnector includes:
A metallic core made of Crofer 22 APU.
A supportive ceramic plate made of 3YSZ and 5%wt Al2O3.
The two-part interconnector does not react to produce secondary materials that have higher thermal expansion coefficients than the starting material, thus cracks and pores are not formed in the sealing region.
Compared with the conventional metallic interconnectors, the two-part interconnectors are less expensive to produce and provide better sealing.
To improve the research conducted, the study should look in to testing either different types of metals for the two-part interconnector or add coatings to see if results are affected.
Future research should look in to determining the feasibility of a multicell stack for large-scale use in SOFC.

43. References Main research:
Research 1:
Research 2:
Research 3:
Research 4:
Supplementary resources: