Current distribution at porous electrode-solid oxide electrolyte interface

A two-dimensional model is developed fur transport of oxygen in a porous solid oxide fuel cell (SOFC) cathode with negligible oxygen ion conductivity in the bulk. Adsorption and surface diffusion of oxygen adsorbates on the pore walls, interfacial diffusion of adsorbates, and electrochemical reaction kinetics at the electrode/electrolyte interface are considered, as well as the nonuniform current and potential distribution in the electrolyte. In particular; the effect of a nonuniform current distribution along the electrode/electrolyte interface is investigated. The results are compared to a previously developed one-dimensional model for SOFC perovskite cathodes based on the porous electrode theory. The two models agree well, except in the case of strong interfacial mass-transfer limitations. The benefit of an expanded reaction zone along the electrode/electrolyte interface is demonstrated. However, nonuniform current distribution at high current levels caused by diffusion limitations at the interface reduces the effective size of the reaction zone and restricts this zone close to the three-phase boundary.