Microstructure and performance investigation of a solid oxide fuel cells based on highly asymmetric YSZ microtubular electrolytes

A combined phase inversion and sintering technique was used to fabricate highly asymmetric yttria-stabilized zirconia (YSZ) hollow fibers with a 1.9 mm external diameter and 210 μm total wall thickness. These consisted of a thin (∼10 μm), dense outer layer and a much thicker (∼200 μm) inner layer with finger-like voids. Such highly asymmetric structures formed gas-tight electrolytes and mechanical supports of a microtubular solid oxide fuel cell (SOFC). Nickel oxide−yttria-stabilized zirconia (NiO−YSZ) particles were infused into the pores from alcoholic dispersions and then sintered at 1300 °C, prior to electroless Ni layers being deposited, forming composite anodes. The Ni layer deposited by electroless plating had the function of improving the anodic current collection. Cathodes were deposited by slurry-coating lanthanum strontium manganite particles onto the outer surfaces of YSZ hollow fibers, followed by sintering at 1000 °C and reduction of the anode at 800 °C in a hydrogen environment, completing the fabrication of the microtubular SOFCs. Mechanical strengths of ∼226 MPa were derived from three-point bending tests on hollow fibers sintered at 1450 °C. Initial SOFC performance measurements with 5% H2 as the fuel and air as the oxidant resulted in maximum power densities of 18 mW cm−2 at 800 °C. This low value resulted largely from the discontinuous nature of the electrolessly deposited nickel anode; present work aims to improve its structure and hence SOFC performance.