The application of 3D imaging techniques, simulation and diffusion experiments to explore transport properties in porous oxygen transport membrane support materials

Tortuosity plays a vital role in diffusive mass transport through porous layers of electrochemical devices. However, tortuosity cannot be measured directly which is why different methods have been developed to determine the tortuosity of porous samples. These methods differ considerably from each other in terms of calculation approach and applied data sets. Here, we utilise advanced tomography techniques, simulation and diffusion cell experiments to calculate tortuosity of a porous support layer of an oxygen transport membrane (OTM). The results are then compared and the suitability of these different approaches is evaluated. We conclude, that image and simulation based methodologies arrive at lower tortuosity values in comparison to diffusion cell experiments; the difference, depending on the calculation method, can be close to a factor of two. The difference may stem from Knudsen diffusion effects which currently are not accounted for in the image based modelling techniques. Moreover, tortuosity values extracted via diffusion cell experiments are a function of gas mixture and temperature. As a result, one has to distinguish between geometric tortuosity and diffusive tortuosity used for quantifying the resistance of a structure to a flux. (C) 2016 Published by Elsevier B.V.