Plasma-sprayed 3.9YSZ porous coatings with mille-feuille structure and high composite porosity for SOFC applications

A porous coating process for direct-oxidation solid oxide fuel cell (SOFC) electrodes that reduces manufacturing costs and production time is proposed. The process uses Al alloy–polyester as a pore former to create a mille-feuille structure and high porosity in plasma-sprayed 3.9 mol% yttria-stabilized zirconia (3.9YSZ) coatings. With an insufficient amount of pore former (35 vol.%), the as-sprayed coating surface has a higher surface roughness (Ra = 12–13 μm). When a sufficient amount of pore former (50 vol.%) is used, the as-sprayed coating surface roughness (Ra) is 10–11 μm. Apparent porosities in the range of 41.2 to 56.4 vol.% are obtained for the etched and burned plasma sprayed coating. The porosity created with a sufficient amount of pore former (50 vol.%) is significantly higher than that created with an insufficient amount (35 vol.%). The monoclinic phase originally in the 3.9YSZ feedstock powder almost completely disappears after plasma spraying.