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In this paper we combine a stochastic 3D microstructure model of a fiber based gas diffusion layer of polymer electrolyte fuel cells with a Lattice Boltzmann model for fluid transport. We focus on a simple approach of compressing the planar oriented virtual geometry of paper-type gas diffusion layer from Toray. Material parameters -permeability and tortuosity -are calculated from simulation of one phase, one component gas flow in stochastic geometries. We analyze the statistical spread of simulation results on ensembles of the virtual geometry, both uncompressed and compressed. The influence of the compression is discussed with regard to the Kozeny-Carman equation. The effective transport properties calculated from transport simulations in compressed gas diffusion layers agree well with a trend based on the Kozeny-Carman equation.

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The passage of an electrical current through phosphoric acid doped polymer membranes involves parasitic migration of the acid, which imposes a critical issue for long-term operation of the high temperature polymer electrolyte membranes fuel cell (HT-PEMFC). To elucidate the phenomenon, a three-layered membrane is constructed with embedded micro reference electrodes to measure phosphoric acid redistribution in a polybenzimidazole based membrane. Under a constant load, a concentration gradient develops due to the acid migration, which drives the back diffusion of the acid and eventually reaches a steady state between migration and diffusion. The acid gradient is measured as a difference in local ohmic resistances of the anode-and cathode-layer membranes by electrochemical impedance spectroscopy. The phosphoric acid diffusion coefficient through the acid doped membrane is about 10 −11 m 2 s −1 , at least one order of magnitude lower than that of aqueous phosphoric acid solutions. The anion (H 2 PO 4 − ) transference number is found to range up to 4% depending on current density, temperature and atmospheric humidity of the cell, implying that careful control of the operating parameters is needed in order to suppress the vehicular proton conduction as a degradation mitigation strategy.

We performed Monte Carlo simulations to study the adsorption behavior of a small flexible model surfactant on hydrophilic surfaces. A coarse-grained lattice model was used to account for excluded-volume effects and nearest-neighbor interactions. The model predicts adsorption isotherms that agree qualitatively with experimental results. The results of the simulation complete and support experimental structure investigations made with AFM, ellipsometry, and neutron reflectometry. Adsorbed bilayer structures depend on the adsorption energy. The efficiency of hydrophobization and the shielding against small polar molecules increase strongly with increasing surfactant concentration.

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