Feasibility evaluation of low-temperature deposited thin-film electrolyte with successive post-annealing for solid oxide fuel cells

During the past decade, thin-film-based solid oxide fuel cells (TF-SOFCs) have demonstrated remarkable performance at a low operating temperature of ∼500 °C by reducing ohmic resistance with vacuum-deposited thin electrolytes. However, a high-temperature deposition process at approximately 700 °C is employed in TF-SOFCs, which is only available at a laboratory scale and is not appropriate for commercial deposition equipment. To address this issue, we investigate the feasibility of depositing electrolytes at relatively low temperatures (≤300 °C) accompanied with post-annealing. A TF-SOFC comprising a trilayer thin-film electrolyte, i.e., yttria-stabilized zirconia (YSZ) sandwiched between gadolinia-doped ceria (GDC), fabricated at low-temperature deposition with subsequent post-annealing is selected and tested. Based on a thorough examination using X-ray diffraction and scanning electron microscopy, the appropriate growth conditions for the YSZ and GDC thin-film layers are selected. Through the optimization, we successfully create a low-temperature deposited 750 nm-thick GDC/350 nm-thick YSZ/150 nm-thick GDC (CZC) trilayer electrolyte exhibiting comparable performances with that deposited at 700 °C. High performance of a single cell, a peak power density of 890 mW/cm² at 500 °C, is achieved. This result suggests the potential of fabricating high-quality TF-SOFCs with commercial equipment.