Solid oxide fuel cells (SOFCs) are one of the options as auxiliary power units (APU) in transportation, e.g. in vehicles or in aircraft. In particular, metal supported SOFCs consisting of metallic frames and substrates coated with plasma sprayed functional layers have shown an excellent stability concerning redox cycling. In order to provide sufficient power, these single cells have to be assembled to stacks. To prevent short-circuiting the frame of each cell has to be electrically insulated from the neighbouring one. For that purpose a ceramic coating is applied on each metal frame by thermal spraying before it is brazed to other stack components. Such layers should at one hand show good wetting and adhesion to the silver based brazing materials. On the other hand it should maintain sufficient electrical resistance even at the fuel cell operating temperature. As the applied solder, which connects the cells and seals the gas manifold simultaneously, is an excellent electrical conductor, it is mandatory to prevent the brazing material from penetrating into the deposit. In this paper a description of the design and experiences with these plasma sprayed insulating layers is given.

Reliable and economically efficient processes are necessary for the production of high quality coatings for solid oxide fuel cells (SOFC) applications in an industrial scale. In that perspective, Sulzer Metco developed several coating solutions through different processes adapted for each specific applications, in particular on metal supported cells (MSC). Diffusion barrier layers (DBL) using perovskite material, such as Lanthanum Strontium Manganite (LSM), is produced “state-of-the-art” as coating service by Sulzer Metco on metallic interconnects (IC) using the Triplex technology. The newly developed TriplexPro-200 having a long lifetime performance and specific features, like cascaded arc and 3-cathode torch, is the best candidate for producing high quality and reliable coatings in a mass production of SOFC functional layers. LPPS-Thin Film, on the other hand is the technology of choice to deposit very dense, thin and homogeneous layers on various substrates. Yttria stabilized Zirconia (YSZ) layers of 20-40 µm thickness have been deposited on thin metallic substrates (0.7 mm, 140 cm 2 ) without producing any strong deformation of the substrate. Considering the dimension of the metallic substrate the coated cells present very good gas leak tightness performances between 2 and 8 Pa·m/s which is homogeneous on the substrate area. Moreover, LPPS-TF can also be used to produce very dense and thin LSM coatings on interconnects. In this case, LPPS-TF not only produces denser and thinner coatings but also becomes again competitive when considering the manufacturing of DBL for metallic ICs on a high production scale. This paper presents the current developments of these technologies in the domain of SOFC applications.

Solid oxide fuel cell are being widely considered as the promising answer to the fossil energy decrease. To achieve high efficiency and longevity for SOFC stack it is essential to maintain stable hermetic sealing. In order to obtain an efficient airtightness between two SOFC layers, the authors had developed a solid seal composed with a ceramic matrix charged with glass particles. The seal is plasma-sprayed using low-cost manufacturing methods such as atmospheric plasma spraying. This technical deposit can be plasma-sprayed on a wide range of substrates: whatever its nature and shape. It is solid, distortable and adhesive to its support at ambient temperature. The sealing properties are acquired when the SOFC is put into service: the glassy phase migrates into the peculiar plasma-sprayed microstructure of the ceramic matrix towards the interface involving the airtightness. The performance of this seal are pretty good: the leak rate observed at 70 mbar is 0.0042 mbar.l/s whereas the preconisation of the US Department of Energy is 0.005 mbar.l/s.

The potential of atmospheric plasma spraying (APS) technology has been investigated for the manufacture of anode, electrolyte and cathode of a solid oxide fuel cell. As substrates tape-casted or commercial available porous plates both made of a FeCr-alloy were used. The functional layers were applied by atmospheric plasma spraying, however, it turned out that screen printed LSCF cathodes performed better than thermally sprayed versions. Anode layers with high electrochemical activity could be produced by APS using separate injections of NiO and YSZ powders. The manufacturing of gas-tight electrolyte layers was a key-issue of the present development. With adequate processing conditions and advanced gun technology it was possible to produce highly dense ceramic coatings with a very low amount of micro-cracks and pores. These electrolytes gave high open cell voltages above 1 V corresponding to the low measured leakage rates (<10-3 mbar*l/s) of the rather thin (<50 µm) coatings. Additional layers have been applied to reduce the interdiffusion especially of species from the metallic substrates into the anode. These layers could significantly reduce degradation of the cells. SOFCs with a power density at 800°C well above 0.7 W/cm² could be produced by the developed technology.

Metal-supported solid oxide fuel cells (SOFC) composed of a Ce 0.8 Sm 0.2 O 2-δ (SDC) electrolyte layer and Ni- Ce 0.8 Sm 0.2 O 2-δ (Ni-SDC) cermet anode were fabricated by suspension thermal spraying on Hastelloy X substrates. The cathode, a Sm 0.5 Sr 0.5 CoO 3 (SSCo)-SDC composite, was screen-printed and fired in-situ. The anode was produced by suspension plasma spraying (SPS) using an axial injection plasma torch. The SDC electrolyte was produced by high-velocity oxy-fuel (HVOF) spraying of liquid suspension feedstock, using propylene fuel (DJ- 2700). The emerging technology of HVOF suspension spraying was here explored to produce thin and low-porosity electrolytes in an effort to develop a cost-effective and scalable fabrication technique for high-performance, metal-supported SOFCs. In-flight particle temperature and velocity was measured for a number of different gun operating conditions and standoff distances and related to the resulting microstructures. At optimized conditions, this approach was found to limit material decomposition, enhance deposition efficiency and reduce defect density in the resulting coating, as compare to previous results reported with SPS. Produced button cells showed highly promising performance with a maximum power density (MPD) of 0.5 Wcm -2 at 600°C and above 0.9 Wcm -2 at 700°C, with humidified hydrogen as fuel and air as oxidant. The potential of this deposition technique to scale-up the substrate size to 50 X 50 mm was demonstrated.

Perovskite-type LSM and LSCF deposits were developed for oxygen electrode for solid oxide fuel cell and high temperature water electrolyzer by atmospheric plasma spraying (APS) using different feedstock powders. The deposits were tailored to exhibit high oxygen catalytic activity, oxygen surface exchange and diffusion rates, gas permeability and electronic-ionic conductivity. Deposits did not exhibit undesired secondary phases that may form in plasma. Promoting partial melting of the surface of the particles ensured interlayer cohesion and very porous deposit. In SOFC mode cells with LSCF cathodes operating at 800 °C had more than 700 mW/cm² power densities at 0.7 V, which was 35% better than that of cells with LSM cathode. When operating in electrolyzer mode at 800 °C the cells with LSCF oxygen electrode also proved significantly enhanced electrochemical performance compared to cells with LSM oxygen electrode. At a current density of 1 A/cm 2 the voltage for water splitting was reduced to around 1.4 V at an operating temperature of 800 °C and to 1.28 V at 850 °C.

Ni-Al 2 O 3 cermet supported tubular solid oxide fuel cell (SOFC) has been fabricated by thermal spraying processes to aim at reducing fabrication cost. Ni-Al 2 O 3 cermet support was deposited by flame spraying and the anode, electrolyte and cathode were deposited by plasma spraying on the support tube. YSZ-Ni was used as the anode and lanthanum strontium manganate was used as the cathode. Plasma-sprayed ScSZ and YSZ deposits, after post-spray densification treatment by nitrate solution, were used as the electrolyte at thicknesses of 40 µm to 100 µm to assemble SOFC single test cell. It was found that the output power density was increased with the decrease of electrolyte thickness. The cells assembled with ScSZ exhibited a higher powder density than YSZ electrolyte. The maximum output powder density reached 0.89 W/cm 2 with ScSZ electrolyte of 40 µm thick at 1000°C in comparison of 0.76 W/cm 2 obtained with YSZ electrolyte. The results showed that the tubular SOFC fabricated fully by thermal spray processes exhibits excellent performance.

An axial injection suspension plasma spray system has been used to produce layers of fully stabilized yttria-stabilized zirconia (YSZ) that could be used as solid oxide fuel cell (SOFC) electrolytes. Suspension plasma spraying is a promising technique for the rapid production of coatings with fine microstructures and controlled porosity without requiring a post-deposition heat treatment. This new manufacturing technique to produce SOFC active layers requires the build up of a number of different plasma sprayed SOFC functional layers (cathode, electrolyte and anode) sequentially on top of each other. To understand the influence of the substrate and previously-deposited coating layers on subsequent coating layer properties, YSZ layers were deposited on top of plasma sprayed composite lanthanum strontium manganite (LSM)/YSZ cathode layers that were first deposited on porous ferritic stainless steel substrates. Three layer half cells consisting of the porous steel substrate, composite cathode, and suspension plasma sprayed electrolyte layer were then characterized. A systematic study was performed in order to investigate the effect of parameters such as substrate and cathode layer roughness, substrate surface pore size, and cathode microstructure and thickness on electrolyte deposition efficiency, cathode and electrolyte permeability, and layer microstructure.