Multi-length scale microstructural design of micro-tubular Solid Oxide Fuel Cells for optimised power density and mechanical robustness.

In this study, we aim to parametrically reveal the dependence of electrochemical performance on a variety of microstructural characteristics at multi-length scale in a micro-tubular solid oxide fuel cell to shed light on the advanced electrode design. Numerical Direct Simulation Monte Carlo method is used on the tomographically-reconstructed 3D microstructure of the anode to characterise the tortuosity factors as a function of the porosity and pore diameter accounting for the Knudsen flow. These are subsequently incorporated in the mass transport in 2D electrochemical simulations. Results show that the Knudsen tortuosity factor is two times larger than that estimated by the continuum physics. High substrate porosity and pore size show unnoticeable effect in facilitating the mass transport provided that the micro-channels span over 60% of the radial thickness. The width and radial distribution of the micro-channels have little influence on the mass transport, but the compactness greatly affects the global performance. Optimal designs are identified as i) 80% micro-channel length and 27% substrate porosity to reach maximum power density (1.18 W cm−2) with lowered mechanical strength, or ii) 60% micro-channels length and 27% porosity to obtain a more balanced performance (0.96 W cm−2) with better long-term structural integrity. Image 1 • Knudsen tortuosity factor is two times larger than that obtained by continuum flow. • Channels length should be 60% of the anode thickness to eliminate the H 2 depletion. • 10% longer micro-channels yield similar mass flux as 5% less anode porosity does. • The width of the micro-channels is insignificant in enhancing the mass transport. • Hierarchical electrode optimisation scheme is proposed for different applications. [ABSTRACT FROM AUTHOR]