Effects of microstructural functional layers and shielded slots on solid oxide fuel cells

Abstract

A three-dimensional heat/fluid flow analysis procedure to predict the planar SOFC performance using a micro-scale electrode model has been developed. The continuity, Navier-Stokes, energy and species equations, coupled with the electro-chemical relation models, are solved for the single periodic module of a unit cell which is composed of the anode/cathode channels, the porous electrodes, the electrolyte, and the interconnect. Using the FVM method of SIMPLE type, the local current density, which is proportional to the rate of chemical reaction, is determined iteratively by forcing the local current density and the mass-transfer rate at the reacting surface match. The cell characteristics, which include the local current density, temperature, and concentration distributions, are presented and discussed. SOFC electrodes essentially include two types of layers: a structural layer and a functional layer. The structural layers, which are the anode support layer (ASL) and the cathode current collector layer (CCCL), are composed of large particles with a high porosity that facilitates gas diffusion. The functional layers consist of small particles with a low porosity that increases the triple phase boundary (TPB) reaction area and reduces the activation overpotential. In the model, the particle diameter and functional layer thickness are adjusted and analyzed. The effects of the two parameters on the performance of the functional layer are monitored in the contexts of several multilateral approaches. Most reactions occurred near the electrode-electrolyte interface; however, an electrode design that included additional TPB areas improved the electrode performance. The role of the functional layer in a SOFC is examined as a function of the functional layer particle size and thickness. The performance of a cell could be enhanced by preparing a functional layer using particles of optimal size and thickness, and by operating the device under conditions optimized for these ...