Gastight Yttria-Partially Stabilized Zirconia Layers Manufactured by Suspension Plasma Spraying for SOFC Electrolyte Functional Layers

Solid oxy-fuel cells (SOFCs) should permit efficient energy conversion and emissions of non-GHGs for energy production in housing (horizon 2015) and transportation (horizon 2030). Moreover, based on closely-related designs, high temperature electrolyze (HTE) should permit to produce H₂ at a relatively high efficiency. SOFCs include in their design a solid electrolyte layer made of Yttria-Partially Stabilized Zirconia (Y-PSZ) or apatites acting as an ionic conductor and through which oxygen ions diffuse. This layer needs to fulfill several characteristics among which a low leakage rate corresponding to a non-connected pore network and a low level of stacking defects such as microcracks or globular pores. Moreover, the thickness of this layer needs to be as low as possible (about 10 µm) in order to limit ohmic losses. Suspension Plasma Spraying (SPS) appears as a possible technological route to manufacture such layers structured at the micrometer or sub-micrometer scales. In SPS, a stabilized suspension, made of a solvent, solid particles and a dispersant, is injected within the plasma flow. The liquid is very quickly fragmented and then vaporized and the individual particles, or the particle agglomerates, depending on the average size and morphology of the solid feedstock, are heated and simultaneously accelerated towards the substrate surface where they impact, spread and solidify, analogously in a first approximation to larger particles, to form a layer. The architecture of the layer, in particular its pore network, is very closely related to plasma operating parameters (from which derive plasma flow stability), from the suspension characteristics, in particular the feedstock particle size distribution, from the torch / substrate kinematics and from the suspension injection parameters. This work aims at presenting recent developments made to optimize some of these operating parameters to maximize the electrolyte layer characteristics, in particular its gas tightness.