Using 3D imaging and electrochemical modelling to design and optimise electrode performance

Solid oxide fuel cells (SOFCs) are some of the most promising electrochemical devices in terms of clean and efficient energy production. At the SOFC anode, fuel is oxidised without an intermediate combustion process at the triple-phase boundaries (TPBs) between metal, ceramic and porous phase. These three different phases have a porous and complex microstructure, whose changes upon operation and degradation have yet to be fully related to bulk measurements, such as impedance spectroscopy (EIS) measurements, commonly used to assess cell performance. In this work we use time-lapse 3D imaging in close association with electrochemical modelling to move towards intelligently designing electrode structures. A porous scandia stabilised zirconia (ScSZ) scaffold was fabricated using tape casting, impregnated with Ni and characterised with FIB-SEM in order to obtain 3D microstructural parameters such as phase fractions, phase connectivity and tortuosity, and the length and density of the TPBs. The 3D microstructural parameters were used as an input in a 1D electrochemical model to predict both the changes in EIS spectra upon microstructure degradation in a reduced atmosphere as well as the strategies of microstructure optimisation needed for improved performance. Symmetrical cells were set up to compare experimental EIS spectra with the performance predicted by the electrochemical model. The degraded electrode morphology was characterised in 3D and both the model and the experimental results show a factor of three decrement in the TPB density related to the decline in performance during degradation. Following the model suggestion, new electrodes were fabricated and cycled to check for performance improvements. This approach enables the move towards intelligently designed structures with attributes tailored towards optimised performance.