Ostadi-Valiabad, Hossein (2012)
Ph.D. thesis, University of Birmingham.
This PhD project is a step change towards the fluid flow prediction within the polymer electrolyte fuel cells through micro/nano characterisation of porous layers of the fuel cell. X-ray micro/nano tomography has been developed to reveal a three dimensional digital image of gas diffusion layers at micro/nano scale and focused ion beam/scanning electron microscope nanotomography technique was developed to visualize the three dimensional porous structure of the microporous layer and catalyst layer. Tomography images then were used to obtain morphological parameters of the layers and combined with well-known analytical models and numerical-simulations to anticipate the permeability, diffusivity and tortuousity of the layers. The project can be divided into two main sections. In the first section X-ray micro and nanotomography were used to characterise the uncompressed gas diffusion layers. In addition, the structural features of compressed gas diffusion layers were captured by using polydimethylsiloxane to encapsulate the compressed porous structure and by subsequently employing X-ray microtomography to reconstruct a digital three dimensional model. In the second section, focused ion beam/scanning electron microscope nanotomography was developed for the microporous layer and the catalyst layer. The techniques were successfully applied to other materials including glass micropipettes, metals, silicon, urine catheters and diatomaceous frustules.
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