Solid oxide cell electrolytes deposited by atmospheric suspension plasma spraying at high velocity and high temperature

Abstract

Metal-supported solid oxide cells with Yttria-stabilized zirconia (YSZ) electrolytes fabricated by atmospheric plasma spraying are routinely found to have open-circuit voltages (OCVs) below the Nernst potential due to gas crossover and combustion resulting from electrolyte defects. To improve splat bonding and reduce coating defects, YSZ electrolytes were fabricated here at >800 • C substrate temperatures and torch-substrate relative velocities of 4 and 12 m/s by atmospheric suspension plasma spraying. Electrolyte microstructures appeared dense, with porosities estimated to be approximately 2.2-3.5 vol%. Minimal segmentation cracking was observed on samples fabricated at 12 m/s. The full cells that were electrochemically tested had permeabilities in the range of 4-6 × 10 −19 m 2 , and the maximum recorded OCV was ∼26 mV below the Nernst potential for 750 • C. Potential performance gains from YSZ deposition at substrate temperatures >800 • C may have been masked by poor substrate-fuel electrode contact. Using electrochemical impedance spectroscopy, it was found that the ohmic and polarization resistances decreased and increased, respectively, over time. The calculated distribution of relaxation times of the tested cells, together with observations from the literature, were employed to identify possible cell degradation mechanisms observed during short-term durability testing.