Microstructure-controlled deposition of yttria-stabilized zirconia electrolyte for low temperature solid oxide fuel cell performance stability enhancement

Yttria-stabilized zirconia thin films were deposited with a controlled argon flow rate via DC reactive magnetron sputtering processes. Typically, thin film electrolytes fabricated by physical vapor deposition onto nano-porous substrates generate pinholes due to their columnar grain structure. The grain boundaries between these columnar grains can be considered as structural defects and can cause voltage drops due to electrical shorting when used as thin film electrolytes in energy conversion systems. By controlling the argon flow rate of the reactive sputtering method, YSZ thin films with dense and restrained columnar grains were fabricated. Scanning electron microscopy inspection was conducted to analyze the surface morphologies, grain structures, and nano-defects in the interior of YSZ thin films. X-ray photoelectron spectroscopy revealed that the composition of the YSZ electrolyte is determined by the flow rate of the oxygen-reactive gas. In addition, X-ray diffractometry was conducted to verify the crystalline phase of the YSZ films; it was determined that a lower argon flow rate produces a better crystalline phase. The films also showed high ionic conductivity compared to the reference data, and the restrained columnar structure had higher conductivity due to a reduction in the ion transport blockage. Furthermore, the fuel cell with the YSZ electrolyte fabricated under a low argon flow rate, which had restrained columnar grains, showed a higher peak power density and superior open circuit voltage performance compared to the fuel cell with a higher argon flow rate.