Three-dimensional phase segregation of micro-porous layers for fuel cells by nano-scale X-ray computed tomography

Abstract Modern hydrogen powered polymer electrolyte fuel cells (PEFCs) utilize a micro-porous layer (MPL) consisting of carbon nanoparticles and polytetrafluoroethylene (PTFE) to enhance the transport phenomena and performance while reducing cost. However, the underlying mechanisms are not yet completely understood due to a lack of information about the detailed MPL structure and properties. In the present work, the 3D phase segregated nanostructure of an MPL is revealed for the first time through the development of a customized, non-destructive procedure for monochromatic nano-scale X-ray computed tomography visualization. Utilizing this technique, it is discovered that PTFE is situated in conglomerated regions distributed randomly within connected domains of carbon particles; hence, it is concluded that PTFE acts as a binder for the carbon particles and provides structural support for the MPL. Exposed PTFE surfaces are also observed that will aid the desired hydrophobicity of the material. Additionally, the present approach uniquely enables phase segregated calculation of effective transport properties, as reported herein, which is particularly important for accurate estimation of electrical and thermal conductivity. Overall, the new imaging technique and associated findings may contribute to further performance improvements and cost reduction in support of fuel cell commercialization for clean energy applications.

[1]  Toshiaki Konomi,et al.  Microporous layer coated gas diffusion layers for enhanced performance of polymer electrolyte fuel cells , 2010 .

[2]  Rui Chen,et al.  3D reconstruction of a gas diffusion layer and a microporous layer , 2010 .

[3]  R. Zengerle,et al.  Direct three-dimensional reconstruction of a nanoporous catalyst layer for a polymer electrolyte fuel cell , 2011 .

[4]  A. Bazylak,et al.  Synchrotron Investigation of Microporous Layer Thickness on Liquid Water Distribution in a PEM Fuel Cell , 2015 .

[5]  K. Ueda,et al.  Phase-contrast X-ray imaging of the gas diffusion layer of fuel cells. , 2010, Journal of synchrotron radiation.

[6]  David J. Hawkes,et al.  X-ray attenuation coefficients of elements and mixtures , 1981 .

[7]  I. Manke,et al.  3D Visualisation of PEMFC Electrode Structures Using FIB Nanotomography , 2010 .

[8]  Ned Djilali,et al.  Micro-porous layer stochastic reconstruction and transport parameter determination , 2015 .

[9]  Matthew M. Mench,et al.  Effect of material properties on evaporative water removal from polymer electrolyte fuel cell diffusion media , 2010 .

[10]  Rui Chen,et al.  Influence of threshold variation on determining the properties of a polymer electrolyte fuel cell gas diffusion layer in X-ray nano-tomography , 2010 .

[11]  Ravindra Datta,et al.  Understanding the gas diffusion layer in proton exchange membrane fuel cells. I. How its structural characteristics affect diffusion and performance , 2014 .

[12]  I. Manke,et al.  3D microstructure modeling of compressed fiber-based materials , 2014 .

[13]  E. Kjeang,et al.  A customized framework for 3-D morphological characterization of microporous layers , 2013 .

[14]  Adam Z. Weber,et al.  Probing water distribution in compressed fuel-cell gas-diffusion layers using X-ray computed tomography , 2015 .

[15]  S. Lee,et al.  Tomographic analysis of porosity variation in gas diffusion layer under freeze-thaw cycles , 2012 .

[16]  S. Litster,et al.  Resolving the Three‐Dimensional Microstructure of Polymer Electrolyte Fuel Cell Electrodes using Nanometer‐Scale X‐ray Computed Tomography , 2012 .

[17]  E. A. Wargo,et al.  Comparison of focused ion beam versus nano-scale X-ray computed tomography for resolving 3-D microstructures of porous fuel cell materials , 2013 .

[18]  Adam Z. Weber,et al.  Effects of Microporous Layers in Polymer Electrolyte Fuel Cells , 2005 .

[19]  A. Phillion,et al.  X-ray Tomographic Analysis of Porosity Distributions in Gas Diffusion Layers of Proton Exchange Membrane Fuel Cells , 2015 .

[20]  M. Bahrami,et al.  An analytical relationship for calculating the effective diffusivity of micro-porous layers , 2015 .

[21]  Chao-Yang Wang,et al.  Two-Phase Transport in Polymer Electrolyte Fuel Cells with Bilayer Cathode Gas Diffusion Media , 2005 .

[22]  N. Djilali,et al.  Effect of Polytetrafluoroethylene (PTFE) and micro porous layer (MPL) on thermal conductivity of fuel cell gas diffusion layers: Modeling and experiments , 2014 .

[23]  Chung-Jen Tseng,et al.  Effects of microstructure characteristics of gas diffusion layer and microporous layer on the performance of PEMFC , 2010 .

[24]  Bryan S. Pivovar,et al.  Imaging of Water Profiles in PEM Fuel Cells Using Neutron Radiography: Effect of Operating Conditions and GDL Composition , 2007 .

[25]  F. Marone,et al.  Implications of polymer electrolyte fuel cell exposure to synchrotron radiation on gas diffusion layer water distribution , 2014 .

[26]  Marco Stampanoni,et al.  Investigation of liquid water in gas diffusion layers of polymer electrolyte fuel cells using X-ray tomographic microscopy , 2011 .

[27]  E. Kjeang,et al.  Stochastic Microstructural Modeling of PEFC Gas Diffusion Media , 2014 .

[28]  D. Wood,et al.  In-Plane Mass-Transport Studies of GDL Variation Using the Segmented Cell Approach , 2009 .

[29]  Surya R. Kalidindi,et al.  Morphological Analyses of Polymer Electrolyte Fuel Cell Electrodes with Nano‐Scale Computed Tomography Imaging , 2013 .

[30]  Volker Schmidt,et al.  Three-dimensional study of compressed gas diffusion layers using synchrotron X-ray imaging , 2014 .

[31]  Perry Sprawls,et al.  Physical principles of medical imaging , 1987 .

[32]  J. Banhart,et al.  Influence of local carbon fibre orientation on the water transport in the gas diffusion layer of polymer electrolyte membrane fuel cells , 2015 .

[33]  Erik Kjeang,et al.  Thermal conductivity of microporous layers: Analytical modeling and experimental validation , 2015 .