Analyzing the Mechanical Performance of Solid Oxide Fuel Cells at Interfacial Anode/Electrolyte Regions Using Sub-Micron Resolution 3D X-Ray Computed Tomography

Abstract

The use of composite Ni-YSZ cermets is now commonplace, the addition of electrolyte ceramic to the electrode is observed to cause non-linear strain when outside of isothermal environments [1], thought to be maximised at the material interfaces [2, 3]. X-ray tomography has proven to be a powerful tool in the characterisation of electrochemical devices, particularly, when inspecting the structural alterations caused by degradation mechanisms [4]. Additionally, in combination with techniques such as digital volume correlation (DVC), strain and material displacement can be mapped in three dimensions with trajectory information [5], improving understanding of material migration under operationally relevant conditions. This work presents the microstructural developments at interfacial regions within a solid oxide half-cell exposed to varying degrees of thermal shock, similar to that which would be expected in operational conditions. The microstructure is analysed with use of lab-based X-ray tomography achieving statistically relevant data with sub-micron resolutions while preserving macroscopic mechanical influence via large sample volumes, ca. 5 x107 μm3. By imaging the same volume sequentially using the authors were able to correlate the structural dynamics within the volume using computational DVC analysis. Figure 1 presents the change in electrolyte angle of an anode supported solid oxide-half cell through increased thermal shock. Various degrees of thermal ramp-rate are examined via X-ray tomography slices and phase percolation network lengths. Decreased connectivity in the electrochemical activity maps within the anode is observed with the increasing electrolyte bowing, resulting in a reduction in the percolated triple phase boundary (TPB) reaction site density. The results here present enhance insight into the real-world mechanical influence of expansion gradients between neighbouring layers during operational thermal cycling. Robinson, J.B., et al., 2015. Journal of Power Sources, 288, pp.473-481.Clague, R., et al., 2011. Journal of Power Sources, 196(21), pp. 9018-9021.Celik, S., et al., 2014. International Journal of Hydrogen Energy, 39(33), pp.19119-19131.Shearing, P.R., et al., 2012. Solid State Ionics, 216, pp.69-72.Finegan, D.P., et al., 2015. Advanced Science. Figure 1 Electrolyte bowing observed in an anode supported Ni-YSZ/YSZ solid oxide half-cell captured using X-ray computed tomography: a) profiles for the four thermal cycles at successively increasing ramp rates of 3, 10, 20 and 30 ᴼC/min, with accompanying single tomograph slices from the b) pre and ci) post-cycling tomograms, cii) magnified electrolyte bowing from the post-cycling tomogram, and d) Ni percolation mapping where white and red paths represent segments longer and shorter than 10 μm respectively. Figure 1