Polarization Effects in Intermediate Temperature, Anode‐Supported Solid Oxide Fuel Cells

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Abstract
Anode‐supported solid oxide fuel cells with yttria‐stabilized zirconia (YSZ) electrolyte, Sr‐doped (LSM) + YSZ cathode, and Ni + YSZ anode were fabricated and their performance was evaluated between 650 and 800°C with humidified hydrogen as the fuel and air as the oxidant. Maximum power densities measured were at 800°C and at 650°C. Voltage (V) vs. current density (i) traces were nonlinear; V vs. i exhibited a concave‐up curvature at low values of i and a convex‐up curvature at higher values of i, typical of many low temperature fuel cells. Analysis of concentration polarization based on transport of gaseous species through porous electrodes, in part, is used to explain nonlinear V vs. i traces. The effects of activation polarization in the Tafel limit are also included. It is shown that in anode‐supported cells, the initial concave‐up curvature can be due either to activation or concentration polarization, or both. By contrast, in cathode‐supported cells, the initial concave‐up curvature is entirely due to activation polarization. From the experimentally observed V vs. i traces for anode‐supported cells, effective binary diffusivity of gaseous species on the anodic side was estimated to be between at 650°C and at 800°C. The area specific resistance of the cell (ohmic part), varied between at 650°C and at 800°C with an activation energy of ∼65 kJ/mol. © 1999 The Electrochemical Society. All rights reserved.

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