Present solid oxide fuel cells (SOFCs) use complex materials to provide (i) sufficient stability and support, (ii) electronic, ionic, and mass transport, and (iii) electrocatalytic activity. However, there is a limited quantitative understanding of the effect of the SOFC's three dimensional (3D) nano/microstructure on electronic, ionic, and mass-transfer-related losses. Here, a nondestructive tomographic imaging technique at 38.5 nm spatial resolution is used along with numerical models to examine the phase and pore networks within an SOFC anode and to provide insight into the heterogeneous microstructure’s contributions to the origins of transport-related losses. The microstructure produces substantial localized structure-induced losses, with approximately 50% of those losses arising from phase cross-sectional diameters of 0.2μm or less.

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Anion exchange membranes (AEMs) are being developed for potential use in fuel cell systems which include portable power applications. In a fuel cell, these membranes transport hydroxide ions from the cathode to the anode. If carbon dioxide is present, carbonate and bicarbonate ions can form, displacing the hydroxide ions. Among the challenges this presents, the carbonate and bicarbonate are less mobile than the hydroxide and therefore the ionic conductivity of the membrane suffers. A procedure is outlined to take data from a permeation based water flux experiment and determine diffusion coefficients and the ionic conductivity of the membrane. The water-membrane diffusion coefficients can be measured from a water flux experiment. Using principles from kinetic theory, the water-membrane diffusion coefficient can be converted to an appropriate ion-membrane diffusion coefficient. Finally, an equation derived from the dusty fluid model can be used to calculate the ionic conductivity of the membrane in different counter ion forms. The calculated ionic conductivities have been shown to agree well with reported values for proton and anion exchange membranes.Anion exchange membrane fuel cells (AEMFCs) have received increased attention in recent years. The AEMFC typically operates at low temperatures, below 80 • C, and can utilize alcohol fuels; making it of possible appeal for portable power applications. Operating in a high pH environment allows for favorable alcohol oxidation kinetics and the ability to use non-platinum oxygen reduction catalysts. 1,2 Despite recent improvements, there are still several challenges confronting the technology. The low hydroxide ionic conductivity of the AEM and the formation of carbonate and bicarbonate species which further reduce the membrane's ionic conductivity are two such challenges that are examined in this study. 3,4 Current AEMs often use a polymer hydrocarbon backbone with benzyl-trimethylammonium fixed side chain groups. This cation is a strong base (pK b ≈ 1) which allows for reasonable dissolution of the hydroxide ions (OH − ) from the membrane and easy transport through the membrane. 5 The polymer backbone can range from several polymers including poly(ethylene-co-tetrafluoroethylene) (ETFE), poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP), polypropylene, and polysulphone. 6-10 In one study, a fully hydrated AEM with an ETFE backbone was reported to have an ionic conductivity of roughly 30 mS/cm at 30 • C. When comparing this to Nafion 115 proton exchange membrane (PEM), which has a similar IEC, the PEM has a much higher ionic conductivity around 90 mS/cm. 7 If carbon dioxide (CO 2 ) is present, then the formation of carbonate (CO 3 −2 ) and bicarbonate (HCO 3 − ) ions can affect the membrane in several ways. One effect is the decrease in pH, which might actually work to increase the stability of the membrane. 6 However, the same ion exchange process also reduces the ionic conductivity of the membrane. This happens because the carbonate species displace the hydroxide ...

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Multi-component gas diffusion in the continuum flow regime is often modelled using the Stefan–Maxwell (SM) equations. Recent advances in lattice Boltzmann (LB) mass diffusion models have made it possible to directly compare LB predictions with solutions to the SM equations. In this work, one-dimensional (1D) and two-dimensional (2D), equi-molar counter-diffusion of two gases in the presence of a third, inert gas is studied. The work is an extension and validation of a recently proposed binary LB model for components having dissimilar molecular weights. The treatment of inflow and outflow boundary conditions (for specifying species mole fractions or mole flux) is developed via the averaging of component velocities before and after collisions. Results for one and two spatial dimensions have been compared with analytic and numerical solutions to the SM equations and good agreement has been found for a wide range of parameters and for large variations in molecular weights. A novel molecular weight tuning strategy for increasing the accuracy has been demonstrated. The model developed can be used to model continuum, multi-component mass transfer in complex geometries such as porous media without empirical modification of diffusion coefficients based on porosity and tortuosity values. An envisioned application of this technique is to model gas diffusion in porous solid oxide fuel cell electrodes.