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Characterization of porous transport layers of polymer electrolyte membrane fuel cells using X-ray micro-computed tomography

University of British Columbia

Among different methods available for the estimation of the transport properties of porous transport layers (PTLs) of polymer electrolyte membrane fuel cells, X-ray micro-computed tomography (X-µCT) imaging has been recognized as a viable tool. This method provides the 3D structure of materials with a high resolution. Despite the general success of X-µCT, the following topics have not been explored: first, the porosity obtained for one PTL sample using different methods varies due to arbitrary assumptions made in finding the surface of PTLs. Second, the minimum volume required to obtain permeability and effective diffusivity has not been introduced. Finally, the effect of the cracks of the micro porous layer (MPL) (i.e., the second layer of a dual-layer PTL) on porosity has thoroughly been studied but not for permeability and effective diffusivity. In this thesis, a robust surface identification method, named as "Rolling Ball", is introduced to systematically identify the surface and consequently to measure the porosity of PTLs. The main advantage of this method is that it uses the carbon fibre radius (instead of arbitrary assumptions) to identify the surface and also preserves the surface roughness by following the topology of the surface. Different 3D image sizes of PTLs are also analyzed using Avizo software to identify the representative volume for which the estimated permeability and effective diffusivity are independent of the size. The results of these analyses are compared to the comprehensive model of Tomadakis-Sotirchos (TS), which shows the TS model overestimates through-plane permeability and effective diffusivity. The effect of the cracks in MPL on permeability and effective diffusivity is studied for PTL samples with MPL and the segmented MPL from the PTL. The permeability and effective diffusivity results show a decreasing trend due to the presence of the MPL, which is similar to the results of numerical models previously developed based on the nanopores of the MPL. The consistency between these results and previous models suggests that the cracks play the major role in the transport properties.

Text

2016-07-08

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/58406

Mechanical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/