Fuel Cells With High Temperature Stability Of The New Type Sealing Glass And Failure Simulation Analysis

Fuel cells convert chemical energy of a fuel gas directly into electrical work, and are efficient and environmentally clean, since no combustion is required. Moreover, fuel cells have the potential for development to a sufficient capacity for applications for commercial electricity generation. Solid oxide fuel cells （SOFC） have two basic designs:tubular and planar, of which the planar design is easy to assemble and with greater power density. However, the planar solid oxide fuel cells （p-SOFC） have to utilize high temperature sealing technology to prevent fuel leakage. As for the sealing process, sealing materials must withstand thermal expansion mismatch and long-term high temperature treatment. Thus, it is really essential to investigate the high temperature stability and reliability of sealing materials.SrO-Al₂O₃-SiO₂-B₂O₃glass system （SASB） is a new type of SOFC sealing material, whose high temperature stability remains to explore. Based on some literature, SASB glass with suitable composition was prepared by conventional melt-quenching method. The crystallization mechanism, long-term phase transformation and high temperature liquidity were analyzed by differential thermal analysis, X-ray diffraction （XRD） analysis and viscosity estimate, respectively. According to crystallization kinetics theory, the activation energy of45SrO-5Al₂O₃-41SiO₂-3La₂O₃-6B₂O₃glass is271kJ/mol, close to traditional BaO-Al₂O₃-CaO-Si₂O₃seal glass. After long-time heat treatment under SOFC service temperature, SASB turns into glass-ceramics with above56%crystalline phase, which help strengthen mechanical strength and chemical stability of SOFC seal structure. The calculation results of glass viscosity indicate the high temperature liquidity meets with design requirement well. Generally, this SASB glass is suitable to operate for a long time under SOFC high temperature condition.The other objective of this paper is to analyze the failure probability of p-SOFC stacked structure by finite element method （FEM）. The major failure types include matrix fracture and interface delaminating. Theoretical analysis for SOFC stacked structure was conducted, and the results showed that the seal matrix was under compressive stress. Then in the finite element model a pre-allocated micro-crack was integrated into the seal matrix near the free surface for propagation prediction using J-integral methodology. Related parameters such as sealing temperature loadings, layer thickness and mismatch of coefficient of thermal expansion （CTE） were analyzed to give assistance in designing cell components. Simulation results indicate that micro-cracks are most prone to propagate in the cooling process just after glass layer is sealed with other components, and their energy release rate is in linear positive correlation with seal thickness. On the other hand, employ cohesive zone model （CZM） to simulate the interface’s state response. It’s found out that the Metal/Glass interfaces damage partially under residual thermal stress, but can’t destroy completely. Therefore the seal interface delaminating can’t occur without consideration of manufacture defects.