A solid oxide fuel cell is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. It involves ionic transport and electrochemical reactions where the electrolyte and electrode properties play a major role in performance, along with a range of complementary materials that need to ensure equally relevant functions across the cell. The lifetime of such functional materials is expected to reach many thousands of hours with minimal degradation. This article is centred around the process development, optimization and scale up of a thin plasma sprayed ceramic barrier layer to mitigate long-term performance degradation of metal-supported solid oxide fuel cells. The evolution from the proof of concept in a laboratory environment to the scale up toward large scale manufacturing production is discussed. The challenges associated with minimizing application time and lowering cost while maintaining high coating performance at high yield are discussed. Empirical observations such as microstructural analysis and in-flight particle monitoring are used to gain understanding of the plasma spray process and guide its development for high-volume production. Results show how this effort has led to the reduction of the coating deposition time by 94% to enable large-scale manufacturing at high yield.

Stabilized bismuth oxide with fluorite structure is considered a promising electrolyte material for intermediate temperature solid-oxide fuel cells (SOFCs) due to its high oxygen ion conductivity. The ternary system, Bi2O3-Er2O3-WO3, is of particular interest because it is ionically conductive as well as thermally stable. This study investigates the quality of Bi2O3-Er2O3-WO3 (EWSB) electrolyte produced by plasma spraying. The phase structure and cross-sectional microstructure of plasma-sprayed EWSB were characterized by XRD and SEM. The as-sprayed EWSB was found to have a dense microstructure with well bonded lamellae. XRD analysis showed the formation of EWSB with δ-phase and a trace of β-phase, while the β-phase disappeared after annealing at 750°C for 10h. Electrical property tests revealed that the plasma-sprayed electrolyte also had excellent ionic conductivity (0.26 S cm-1 at 750 °C), making it a strong candidate for use in SOFCs at intermediate temperatures.

This study investigates the effect of deposition temperature and particle size on lanthanum strontium chromite (LSC) deposits produced by atmospheric plasma spraying. The results show that dense deposits with lamellar interface bonding can be achieved at temperatures above the critical bonding temperature and that particle size has a significant effect on chromium vaporization losses. The loss of chromium may be responsible for the low electrical conductivity of LSC deposits produced from small powders, which suggests that conductivity can be controlled with appropriate process adjustments.

This study assesses the potential of scandia-stabilized zirconia (ScSZ) produced by very low-pressure plasma spraying (VLPPS) for metal-supported solid oxide fuel cell (MS-SOFC) applications. To investigate the microstructure of ScSZ, coating samples were deposited at spraying distances of 150, 250, 350 mm. The fragile nature of coating cross-sections suggests that the typical lamellar structure of zirconia is replaced by a transgranular structure. Nonetheless, apparent porosity, ionic conductivity, open circuit voltage, and ohmic resistance measurements indicate that VLPPS is a viable method for producing MS-SOFCs.

Ni-Co-Al-Li oxide (NCAL) is an important catalyst material for low-temperature solid oxide fuel cells (LTSOFCs). In this paper, air-plasma spray (APS) coating technology was applied to make NCAL layers on porous steel supports for the LTSOFC. The results showed that NCAL was well deposited on the skeletons of the support. Due to the plasma heating, the original LiMO 2 phase transferred to Li-deficient Li 0.4 M 1.6 O 2 phase simultaneously forming Li-rich oxide. New fuel cell structures were designed. The stability of the fuel cells was evaluated by performing galvanostatic test at 500 °C. The influence of the cell structures and quality on the electronic property of the cells was discussed.

High manufacturing costs and long-term degradation are the main problems that have become a “bottleneck” and impeded SOFC’s further development. It is well known that a high operating temperature is the major cause that leads to these problems. As such, reducing the operating temperature becomes a hotspot of research. It has been reported that a uniform and dense coating can be prepared by using very low pressure plasma spraying (VLPPS) technology. The current study focuses on VLPPS for application in large-area (~100 × 100 mm) porous metal supported solid oxide fuel cell (MSSOFC), especially for the preparation of the electrolyte. It was found that the densification of the electrolyte was very good, as confirmed by the open-circuit voltage (OCV) of the cell. In the temperature range of 550~750°C, the OCV of the cell stabilized between 1.05 V and 1.1 V. The power density of the cell was also measured.

Solid oxide fuel cell (SOFC) has been developed for a hundred year and met a great challenge on material design and marketing. In recent years, new SOFC materials are dug up to achieve high energy-output performance at lower working temperature (300~600 °C), namely low-temperature SOFC (LTSOFC). In this study, Ni-Co-Al-Li oxide (NCAL) was used for making dense, thin and uniform coatings on grooved bipolar electrode substrate for LTSOFC. Low-pressure plasma spray (LPPS) technology was applied to manufacture the NCAL coatings. The performance of a fuel cell package using the coated bipolars was tested between 350 and 600 °C, showing 6~8 W power output with 4 single fuel cells (active area of 25 cm 2 ). The LPPS technology is believed to be one of the ultimate ways for manufacturing the thin film/coatings for SOFC applications in future.

LSCF(La0.6Sr0.4Co0.2Fe0.8O3) with a perovskite structure has been widely studied as cathode materials for intermediate solid oxide fuel cell(SOFC). It has well-known excellent electrode performance due to its high ionic and electronic conductivity. However, application of LSCF cathode is likely to be limited by the surface catalytic properties and long term stability. Sr and Co may segregate from LSCF under cathode polarization, leading to increased resistance of the cathode. Oxygen hyper-stoichiometric La2NiO4+δ with a K2NiF4 structure possesses a higher catalytic properties, ionic conductivity and stability compared to LSCF cathode. However, the electrical conductivity of the La2NiO4+δ (76 S cm–1 at 800 °C ) in the IT range are lower than 100 S/cm, which is regarded as the minimum requirement in electrical conductivity for an SOFC cathode. Taking account of both the advantages and disadvantages of the two different cathode materials, and good chemical compatibility of those two cathode materials, it is possible to prepare a composite cathode by infiltrating a thin film of La2NiO4+ä on the porous LSCF to enhance the LSCF cathode performance. Therefore, in this study, the LSCF cathode was deposited by atmospheric plasma spray. The porous LSCF cathode was infiltrated by La2NiO4+δ. The microstructure was characterized by SEM and TEM. The effect of infiltration on the polarization of LSCF cathode was investigated.

Based on the specific structure of tubular solid oxide fuel cell stacks, a good chemical, microstructural and phase stability for the protective coating are required in both the oxidizing and reducing environments. In this work, MnCo2O4 coatings of approximately 150 ìm were deposited onto porous Ni50Cr50-Al2O3 substrate by atmospheric plasma spray (APS) process. The coated samples were tested at 800oC with the coating exposed in air environment and the substrate in H2 environment. Reducing and pre-oxidizing treatments were performed prior to the stability test. Then the tested coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results elucidated that the tested coating had a high structural stability on the upper layer, while presented a reducing microstructure on the substrate side. The surface morphology of 100 hours tested coating indicated that the spinel granules still arranged closely with small particle size of ~ 250 nm and no obvious grain enlargement was observed. According to the cross-section, the upper layer kept stable and dense. While at the underneath region, the microstructure presented to be rather porous. However, the resistance presented a decreasing trend with the extension of exposure duration. After exposure for 95 h, the ASR decreased to 18.5 mΩ·cm2 although a substantial Cr diffusion from the substrate was detected.

Microstructure of cermet support influences significantly the performance and stability of solid oxide fuel cells (SOFCs). The properties required for the support include high electrical conductivity, necessary permeability, good match of thermal expansion with other layers and high temperature strength. In this study, a porous Ni50Cr50-Al 2 O 3 cermet was designed as the support of SOFC. The porous cermet was deposited by flame spraying with a powder mixture of 30%vol Al 2 O 3 and 35%vol Ni50Cr50 and 35%vol polyester. The effect of cermet microstructure on its gas permeability was investigated. The electrical conductivity, thermal expansion coefficient and bending strength of cermet support were also studied. The results showed that the gas leakage rate of the cermet support increased with the increase of polyester content in the starting powder. The thermal expansion coefficient of the composite cermet decreased with the increase of the volume fraction of Al 2 O 3 . Moreover, the electric conductivity of the cermet increased significantly after high temperature sintering, and reached 1015 S/cm after sintering at 1000°C for 15 hours. The three point bending strength of the Ni50Cr50-based cermet support reached 171 MPa. The cermet stability at high temperatures and SOFCs performance were discussed.

Suspension plasma sprayed YSZ coatings were deposited at lab-scale and production-scale facilities to investigate the effect of process equipment on coating properties. The target application for these coatings is SOFC electrolytes, so dense microstructures with low permeabilities were desired. Both facilities had the same torch but different suspension feeding systems, torch robots and substrate holders. These differences meant that the lab facility had higher torch-substrate relative speeds compared to the production facility. When using porous stainless steel substrates with relatively smooth surfaces, permeabilities and microstructures were comparable for coatings from both facilities, and no segmentation cracks were observed. Coating permeability could be further reduced by increasing substrate temperatures during deposition or reducing suspension feed rates. On rougher substrates representative of SOFC cathodes, production facility coatings had higher permeabilities and more segmentation cracks compared to lab coatings. The increased cracking may be due to larger heat impulses with each torch pass at the production facility caused by its lower torch-substrate relative speed. This work highlights some of the challenges associated with scaling up the spray process from the lab to production.

The use of ceramic materials in the production of solid oxide fuel cells (SOFCs) is one of the most innovative applications of these materials in recent years. The aim of this work is to assess how to obtain a complete, self-assembled SOFC (supported by electrolyte) using atmospheric plasma spray (APS) to spray the three different ceramic layers of the assembly. One of the main problems of SOFC production is the high cost of the process; the hypothesis is that these costs can be reduced by forming the three ceramic layers of the SOFC by APS technology. The anode (YSZ-NiO), cathode (LSM), and electrolyte (YSZ) layers can be produced by APS with reasonable efficiency. Another problem with SOFC manufacture is assembly and adhesion of the three layers; the creation of gradual transition layers by APS improves these aspects of the production process. Chemical and structural characterization of the feedstock powders and resultant ceramic layers was performed by laser scattering, XRD, SEM, and confocal microscopy, and the results confirmed the efficiency of the attained APS-SOFC components.

Thermal spray processes are generally employed to deposit dense coatings. The porosity in a thermal spray coating is limited up to about 20% down to less than 1%. The porous abradable coatings can be deposited by using composite powders containing pore-forms such as polymer. Recently, an effective method to deposit porous coating are being developed by directly utilizing semi-melted spray particles through controlling coating surface temperature. In this article, the recent investigations on the deposition of porous materials and ceramic abradable coatings by surface-melted spray particles are reviewed. The bonding formation between particles by controlling deposit surface temperature is essential to form porous deposits. By using flame spraying, different metallic porous deposits up to tens of millimeter thick from refractory molybdenum (Mo) to stainless steel are fabricated with a porosity level up to 70%. Porous alumina (Al 2 O 3 ) and yttria-stabilized zirconia (YSZ) with a porosity of over 60% are deposited for high temperature abradable coating applications directly by semi-molten ceramic particles. The deposition of convex-shaped YSZ particles is employed to construct the high performance structured cathode for solid oxide fuel cell application. Moreover, the deposited convex-shape particles are also utilized to fabricate effective super-hydrophobic surface. The recent progress on the deposition of surface-melted spray particles will enable many new applications for thermal spraying.

SOFCs for mobile applications require short starting times and capability of withstanding several and severe cycles. For such applications metallic cassette type cells with low weight and thermal capacity are beneficial where the active cell part is set in interconnects consisting of two sheets of ferritic steel. These cells are stacked serially to get higher voltage and power. This approach needs interconnect sheets that are electrically insulated from each other to prevent electrical short circuit. The technology discussed here is to use brazed metals, as sealants, and ceramic layers, as electrical insulators, which are vacuum plasma sprayed on the cassette rims. For reliable insulating layers, a variety of deposits were developed, starting from cermet-spinel multilayers with various compositions and constituents, where reactive metals (such as Ti, Zr) were part of the coatings, to pure ceramic layers. The qualities and characteristics of these coatings were investigated which included electric insulation at room temperature and at 800 °C (SOFC operating temperature), wettability of different brazes towards these deposits, phase stability and peeling strength. The single steps of development, characteristics of the insulating layers for SOFCs as well as some challenges that have to be taken into account in the process are described.

In Solid Oxide Fuel Cells (SOFC), thermal spraying has become a preferred process in order to create functional and protective coatings. After a long period of research, SOFC is on the way to become a fully developed technology starting into mass production. Cost aspects of coating generation are becoming decisive. For this reason, thermal spraying has become the preferred process to apply e.g. Manganese Cobalt Iron Oxide (MCF) coatings which prevent the formation of volatile Cr oxides in the SOFC air supply and off-gas. Also Lanthanum Strontium Manganese Oxide (LSM) is now preferentially applied via thermal spraying. The presentation highlights the properties of commercially available spray powders for SOFC, their processing via different spray processes, and the properties of coatings achieved.

The performance of solid oxide fuel cell cathodes can be improved by increasing the number of electrochemical reaction sites. This is often done by controlling microstructures and using composite materials that consist of an ionic conductor and a mixed ionic and electronic conductor. LSCF (La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 -δ) and SSC (Sm 0.5 Sr 0.5 CoO 3 ) cathodes were manufactured by axial-injection atmospheric plasma spraying (APS), and composite cathodes were fabricated by mixing SDC (Ce 0.8 Sm 0.2 O 1.9 ) into the feedstock powders. The plasma power was varied by changing the proportion of nitrogen in the plasma gas. The microstructures of cathodes produced with different plasma powers were characterized by scanning electron microscopy and gas permeation measurements. The deposition efficiencies of these cathodes were calculated based on the mass of the sprayed cathode. Particle surface temperatures were measured in-flight to enhance understanding of the relationship between spray parameters, microstructure, and deposition efficiency.

Nickel – yttria stabilized zirconia coatings and nickel – samaria doped ceria coatings were fabricated by solution precursor plasma spraying using the Northwest Mettech Axial III plasma torch. Three sets of plasma spray parameters were used resulting in comparatively low, intermediate, and high plasma powers of 63 kW, 102 kW, and 152 kW, respectively. The high and low power conditions resulted in powdery type coatings with poor adhesion to the substrate and between particles. The intermediate power conditions resulted in harder coatings with improved adhesion and electrical conductivity.

Suspension plasma spraying (SPS) is regarded as a promising way to produce new coating structures with improved properties. In this study, SPS was studied as a possible manufacturing process for producing thin MnCo 2 O 4 spinel coatings for used as protective coatings in metallic interconnector plates of SOFC’s. Suspension of nanosized MnCo 2 O 4 powder and ethanol was thermally sprayed by using an F4-MB plasma gun with radial suspension feeding. The influence of spraying parameters, such as plasma gas composition, total gas flow, current and spraying distance for coating architecture was studied by using field-emission scanning electron microscopy (FESEM) and X-ray diffraction method (XRD). Spraying parameters had a strong influence on the coating structure and composition. Coating with the most homogenous structure were formed when sprayed with the low energy spraying parameters whereas high energy parameters resulted in formation of a columnar microstructure containing larger cobalt rich areas.

Ceramic layers, such as yttria-stabilized zirconia or scandia-stabilized zirconia, used for functional layers of solid oxide fuel cells, i.e. the gas tight oxygen ion conductive electrolyte or as ceramic component in the porous cermet anode, were obtained by the Solution Precursor Plasma Spray (SPPS) process. The influence of different solvent types on microstructure was analyzed by comparison of coatings sprayed with water-based solution to ethanol-based one. Use of solvent with low surface tension and low boiling point enhances splat formation, coating microstructure and crystalline structure. Parameter adjustment to receive coatings from nitrate solutions with ethanol as solvent was carried out. Results of Raman spectroscopy indicate that an intermediate of both nitrates (zirconyl and scandium nitrate hydrate) was deposited.

Liquid injection plasma spraying is of growing interest for thermal spray applications like thermal barrier coatings and solid oxide fuel cells, since finely structured coatings offer improved properties over conventionally spray ones, for example lower thermal diffusivity and higher catalytic activity. One challenge is the optimization and understanding of the injection process. With a new high speed shadowgraphy setup, the injection and atomization of individual drops was observed and described in detail in this work which is, to our best knowledge, not reported before. A drop atomization cone model is derived from observations. A new modelling approach is developed which allows the prediction of the drop atomization cones by analytical calculations. The simulations are compared to measurements and deviations are explained by neglected effects which will be included in further developments of this model.