Multiphysics-coupled failure mechanism of Solid oxide fuel cell sealants under long-term operation: From microcrack evolution to electrochemical degradation and mechanistic damage

Abstract

Solid oxide fuel cell (SOFC) sealant systems experience significant performance degradation and mechanical damage during prolonged high-temperature operation, which severely impacts their reliability and lifespan. This study investigates the degradation of electrochemical and mechanical performance, along with the microstructural evolution of the SrO–SiO₂–MgO–Al₂O₃ sealant, NiO-YSZ anode, and 430 stainless steel interconnect system over 5000 h of operation. The findings reveal that the SOFC stack exhibits a voltage decay rate of 6.50 % per thousand hours at a current density of 300 mA/cm², with open-circuit voltage degradation reaching 7.82 % after 5000 h. Sealant failure impedes charge transfer and gas diffusion reactions, resulting in a 126.66 % increase in ohmic resistance. The precipitation of Sr₂MgSi₂O₇ and SiO₂ crystal phases in the sealant leads to increases of 75.15 % and 84.26 % in hardness and elastic modulus, respectively. The uneven precipitation of crystal phases also accelerates crack generation. The diffusion and enrichment of Mg, Sr, and Si elements at the sealant-anode interface further facilitate crack propagation. These cracks ultimately penetrate the entire sealant and single cell, leading to the failure of the SOFC structure. Multi-physics field coupled modeling reveals that the Mises stress, creep strain, and damage in SOFC stack components increase with the extent of sealant cracking. When the sealant is completely cracked, the current density of the SOFC at 0.60 V voltage decreases by 34.96 %, which significantly reduces the life of the SOFC stack. This study offers valuable insights for optimizing the design and extending the operational life of SOFC stacks.