Multiscale analysis of Ni-YSZ and Ni-CGO anode based SOFC degradation: From local microstructural variation to cell electrochemical performance

Nickel based fuel electrodes are widely used for commercial solid oxide fuel cells showing a high catalytic activity, despite of involving severe microstructural changes which reduce the system lifetime. Needing a detailed knowledge of such phenomena, the authors compare the behaviour of two state-of-the-art planar cells, Ni-YSZ based anode supported cell and Ni-CGO based electrolyte supported cell, working for 1000 hours under a galvanostatic operation with H₂ rich feed. Following a multiscale approach, the system was analysed in terms of both global performance and local properties. Experimental observations through electrochemical characterization and microstructural analysis laid the basis for developing a physics-based model able to predict the cell operation at reference and aged status. Indeed, the kinetics is expressed as a function of microstructural features and considers the time evolution of some parameters. Ni-based electrode was identified as the first source of degradation due to Ni instability resulting in a reduction of catalytic activity and conductivity, correlated mainly to Ni particle coarsening and migration respectively. Each degradation mechanism prevailed depending on the material structure (i.e., initial particle size and distribution) and imposed working conditions (i.e., temperature, load and gas composition).