Abstract
Gas transport properties are closely related to the tortuosity of the pore network within porous materials. For the first time, this study explores a multi-scale imaging and modelling method to measure the tortuosity of an Solid Oxide Fuel Cell (SOFC) electrode material with pore sizes spanning over hundreds of orders of magnitude. This analysis is normally challenging using image-based techniques, as pores of different sizes may not be easily resolved at the same time using X-ray computed tomography (CT). In this study, a tubular SOFC anode, fabricated by a phase inversion technique, is used to illustrate this approach. A heat flux analogy is used to simulate mass transport and the results show that the embedded large-scale finger-like pores can significantly improve mass transport by providing less tortuous pathways.
Highlights
Gas transport through porous anodes is critical to the electrochemical performance of solid oxide fuel cells (SOFC) as the partial pressures of the reactants and products are closely related to the anode polarization, which significantly contributes to the loss of operating voltage
The porous phase in the spongy layer, which appears as solid phase in Figure 2a, is segmented from the computed tomography (CT) data and imported to Star-CCM+ to simulate the heat transfer driven by the temperature difference from 1000 K (LHS) to 300 K (RHS) (Figure 2b)
By integrating the heat flux on the cross-sectional plane, and dividing it by the heat flow on the cross-sectional plane of the empty volume, the material parameter s/ s is equal to 0.015, which is subsequently used as the thermal conductivity of spongy layer in the anode simulation
Summary
Gas transport through porous anodes is critical to the electrochemical performance of solid oxide fuel cells (SOFC) as the partial pressures of the reactants and products are closely related to the anode polarization, which significantly contributes to the loss of operating voltage. The tortuosity factor (τ) is a material parameter used to characterise gas diffusion resistance due to the tortuous pore volume [2, 3] This effective transport parameter can be obtained by the modelling of mass/heat flux through a 3D porous phase using computational fluid dynamics (CFD) methods [4]. Apart from the controllable pore size in the spongy layer, the exchange of solvent and non-solvent in the hollow fiber generates micro-channels which grow in the radial direction, with a diameter of approximately 20 m. This design can significantly improve gas transport in the anode with little sacrifice of mechanical robustness. The tortuosity factor extracted from the high resolution scan was subsequently used for the simulation of the entire anode
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