Transport in solid oxide porous electrodes: Effect of gas diffusion |
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Authors: | Huiming Deng Minyau Zhou Benjamin Abeles |
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Institution: | Exxon Research and Engineering Co., Annandale NJ 08801, USA |
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Abstract: | We extend our previous treatment of a mixed ionic electronic conductor membrane, consisting of a porous cathode and anode separated by a thin non-porous layer, to the case where mass transport of molecules in the porous electrodes can be the rate-limiting step. The linearized transport equations for the ion-hole pairs in the solid and of the gas molecules in the pores are characterized by the length scales LP = √Ld(1 ? φ)/Sτs and Lg = 2Lp√τsφ/τ(1 ? φ)]Dgcg/DIEci] respectively, where Ld = DIE/K is the length scale that determines the transition from diffusion limited to surface exchange limited transport in the non-porous electrodes, K is the surface exchange coefficient, DIE and Dg are the diffusion coefficients of the ion-hole pairs and of the molecules, ci and cg are the concentrations of the ions and molecules, S is the pore surface area per unit volume, φ the porosity and τs and τ the tortuosities of the solid and pore phases respectively. When Lg Lp, which is the case treated previously, the rate-limiting step in the transport is ionic diffusion and surface exchange. Enhancements in oxygen ion current of two orders in magnitude, over non-porous electrodes, are in principle achievable with porous perovskite MIEC having surface area s = 106 cm?1. When Lg Lp the rate-limiting step is mass transport in the pores and the enhancement in ion current is substantially reduced. |
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Keywords: | Porous electrodes Transport Gas diffusion MIEC |
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