The current paper reports self-healing plasma sprayed Mgspinel (MgAl 2 O 4 ) coatings. The coatings were used for electrical insulation in high temperature fuel cells. A range of potential self-healing additives consisting of SiC+X (where X was BaO, CaO, ZnO, Y 2 O 3 , GeO 2 , Ta 2 O 5 , V 2 O 5 ) were characterized and SiC+Y 2 O 3 was initially selected for coating development. Coatings of spinel with 20wt% additive were developed using vacuum plasma spraying (VPS) or atmospheric plasma spraying (APS). In the developed coatings, self-healing was demonstrated after heat treatment at 1050°C in air for 10 hour. Thermophysical and thermomechanical properties of self-healing coatings were determined and compared to spinel coatings. Lastly, a modelling technique is presented to simulate the effective elastic moduli of the coatings. Numerical results based on microstructural simulations showed good agreement with experimental data.

La 1-x Sr x Co 0.2 Fe 0.8 O 3-δ deposits, of different stoichiometry, were fabricated for SOFC oxygen electrode using atmospheric plasma spraying (APS) with TriplexPro gun. The spraying conditions were developed by correlating, plasma jet characteristics (enthalpy and velocity), in-flight particle properties (temperature and velocity) and deposit quality (phase composition, porosity, coefficient of thermal expansion, electrochemical testing). The optimal cathode deposits exhibited a porosity of about 20 vol.%. The CTE in air flow at 800 °C was, however, 15.6 x 10 -6 K -1 and it was independent of the processing conditions. Electrochemical tests for cathodes were conducted on SOFCs that were produced following metal supported design and had YSZ as electrolyte and NiO+YSZ as anode. At 800 °C, power densities of above 640 mW/cm 2 at 0.7 V were recorded with H 2 /air for cell having La 0.60 Sr 0.40 Co 0.2 Fe 0.8 O 3-δ as cathode. Cells consisting of La 0.58 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ and La 0.78 Sr 0.2 Co 0.2 Fe 0.8 O 3-δ had 479 and 496 mW/cm 2 under similar conditions. Using equivalent circuit diagrams the contribution of different polarizations on the cell performance were separated and cathodes were compared. La 0.60 Sr 0.40 Co 0.2 Fe 0.8 O 3-δ was found to have the best electrochemical performance followed by La 0.58 Sr 0.40 Co 0.2 Fe 0.8 O 3-δ and La 0.78 Sr 0.20 Co 0.2 Fe 0.8 O 3-δ .

This paper describes recent improvements in metal supported solid oxide fuel cells produced by plasma spraying. By optimizing the process, incorporating nano-micro structured electrodes, and introducing additional layers to prevent interlayer diffusion, the power density of these cells has doubled, voltage has increased to 1.1 V, degradation rates have been cut in half, and redox stability has improved. Although upscaling to larger substrates initially caused distortion in the metal supports, the problems were successfully overcome.

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.

Nanostructured YSZ+NiO functional layers for SOFC anodes were developed by air plasma spraying. Spray processing was controlled to conserve finely porous and nanostructure of the feedstock in the deposit. The optimized deposits exhibiting high gas permeability, suitable high temperature electronic conductivity, enhanced triple phase boundaries and catalytic activity. The results were compared with conventional NiO+YSZ and Ni-C+YSZ anodes. YSZ electrolyte layer was deposited onto the anodes for electrochemical testing at 800°C in static conditions. Impedance spectroscopy measurements were performed to collect data on the polarization resistance and catalytic behavior of these anode layers. It was established that enlarged reaction zone, provided by high specific surface area of the nanostructured anodes, and finely porous microstructure, led to lower polarizations and enhanced cell performance by more than 60% compared to conventional cells.

This paper focuses on development of the anode layer for SOFCs by plasma spraying. The composite (cermet) anode, developed by thermal spraying, consisted of nickel and YSZ. The effect of different plasma spraying technologies on the micro structural characteristics and the electrochemical behavior of the anode layer were investigated. Coatings were fabricated by spraying nickel-coated graphite or nickel oxide with YSZ using a Triplex II plasma torch under atmospheric conditions as well as a standard F4-torch under atmospheric or soft vacuum conditions. The investigations were directed in order to have an open micro porous structure, higher electrical conductivity and catalytic activity of anode deposits. Porosity was investigated by measuring the gas permeability. SEM and XRD technologies were applied to examine the morphology, microstructure and composition of the layers. Electrical conductivity measurements were carried out to determine ohmic losses within the anode layer. Most promising layers were analyzed by measuring the electrochemical behavior to obtain information about catalytic activity and performance.

Using a D-optimal design of experiments (DOE), influence of feedstock powder and plasma gases were examined on deposition efficiency, gas tightness and electrochemical behavior of vacuum plasma sprayed YSZ for SOFC electrolytes. In-flight particle temperature and velocity, measured by on-line particle diagnostics, were correlated with plasma and deposit properties. Electrochemical testing of cells was performed to determine the influence of gas tightness and microstructure of electrolyte deposit on cell behavior.