Numerical modeling and analyses of anisotropic diffusion and stresses in polymer electrolyte fuel cell

Mehrtash, Mehdi
A two dimensional, half-cell, non-isothermal, multi-phase model of a polymer electrolyte fuel cell (PEFC) is developed. The model accounts for the acting clamping force on the cell with accompanying effects on gas transport properties and contact resistances. Spatial variations of anisotropic structural and physical properties of gas diffusion layers (GDLs) in both in-plane and through-plane directions are considered. The developed mechanistic model is validated by comparıng its results with the experimental data for voltage-current characteristics and channel-rib current density distribution for the first time in literature. Significant changes are observed in local gas and water concentrations as well as current density profiles with respect to cell compression and humidity ratios of entrant gases. Compression exacerbates the liquid saturation under the rib as a consequence of porosity and permeability reduction. Under compression, phase change rate increases in the cell; degree of supersaturation under the channel escalates leading to a higher condensation rate while degree of undersaturation under the rib increases leading to a higher evaporation rate. Low durability of membranes is one of the major barriers for wide spread commercialization of PEFCs. The swelling effect on durability is one of the key challenges for the fabrication of the catalyst-coated membrane at the heart of the PEFC. Presented in this study were three main contributions that provide insight into the probable locations of failure in the membrane under hygrothermal cycle and external applied force, and the realistic conditions where a combination of both these loadings were applied. Mechanical response of the membrane, subjected to conjugate hygro-thermo-mechanical loadings are observed during fuel cell operation. The effects of different operating parameters as well as individual contributing factors on the local stresses induced in the membrane are identified.  
Citation Formats
M. Mehrtash, “Numerical modeling and analyses of anisotropic diffusion and stresses in polymer electrolyte fuel cell,” Ph.D. - Doctoral Program, Middle East Technical University, 2017.