Advanced sintering of solid oxide fuel cells: Microstructure and interfaces

Sintering in solid oxide fuel cells (SOFCs) is traditionally regarded as a consolidation step. However, grain-boundary topology, crystallographic stabilization, defect chemistry, and interfacial compatibility are established during sintering, pre-determining electrochemical performance and durability. This review repositions sintering as a governing design variable rather than a passive densification process. A unified mechanistic framework classifies sintering strategies by their dominant driving forces: diffusion-controlled thermal equilibration, field- and current-assisted nonequilibrium densification, pressure-mediated low-temperature consolidation, and spatially confined energy-beam processing. This perspective links energy input modality to grain growth, pore collapse, crystallographic evolution, and interfacial reactions across electrolytes, electrodes, and multilayer architectures. Comparative analysis shows that key SOFC bottlenecks, including ohmic loss in ultrathin electrolytes, triple-phase-boundary degradation, and interdiffusion-induced reaction layers, are strongly processing-dependent rather than purely material-intrinsic. Conventional furnace sintering remains robust yet thermally severe, whereas microwave and field-assisted routes provide controllable acceleration. Ultrafast and flash-assisted techniques exploit kinetic asymmetry to suppress coarsening, while cold sintering and sol–gel approaches redefine low-thermal-budget integration. Intense pulsed light and laser-based methods enable spatially selective consolidation with potential relevance to scalable manufacturing, although validation remains limited. These comparisons are compiled in five tables covering paired grain-boundary responses, reported processing conditions, published single-variable sweeps, demonstrated formats and operating records, and route selection across eleven component-and-requirement combinations; a closing section converts them into a five-question selection procedure graded by the confidence of the supporting evidence. By bridging microstructural physics with manufacturability metrics, this review advances a process-informed design paradigm for durable, efficient, and scalable SOFC systems.