연료극 지지형 고체산화물 셀의 제조과정에 따른 전기화학적 성능 최적화 및 열화 메커니즘 분석

Abstract

Solid Oxide Cells (SOCs) are promising high-temperature electrochemical devices that offer high energy conversion efficiency and operate without the need for noble metal catalysts, enabling cost-effective and environmentally friendly energy systems. Hydrogen, as a clean fuel, can be utilized to generate electricity in SOCs. Yttria-Stabilized Zirconia (YSZ) is commonly used as an oxygen ion-conducting electrolyte, and Ni-based cermets are typically employed as fuel electrodes. SOCs utilizing a Ni cermet-supported anode allow for the application of thin electrolytes, thereby significantly reducing ohmic resistance and enhancing power density. However, when ZrO₂-based electrolytes are used, the interdiffusion of La and Sr from the cathode can result in the formation of secondary phases such as LaZrO₃, SrZrO₃, and La₂Zr₂O₇, which degrade ionic conductivity and increase interfacial resistance. To mitigate such reactions, a barrier layer such as Gd₂O₃-doped CeO₂ (GDC) is typically introduced between the electrolyte and cathode, requiring high-temperature co-sintering (1250°C– 1450°C). However, the co-sintering process may also induce undesired reactions between GDC and YSZ, forming secondary phases such as Gd₂Zr₂O₇, which deteriorate electrochemical performance. Additionally, Ni diffusion from the anode into the YSZ electrolyte can lead to phase instability and degradation in conductivity during long- term operation. Despite these challenges, there is limited research addressing processing strategies to suppress interfacial reactions during co-sintering, as well as the impact of Ni diffusion on the ionic conductivity and structural stability of YSZ electrolytes. Therefore, this study aims to investigate the effects of post-sintering treatments at reduced temperatures—enabled through compositional modifications—on the suppression of secondary phase formation and to evaluate the electrochemical performance and degradation mechanisms resulting from Ni diffusion in YSZ-based electrolytes.