The effect of testing geometry on the measurement of cell performance in anode-supported solid oxide fuel cells - The effect of cathode area

A simple, approximate analysis of the effect of different cathode and anode areas on the measurement of cell performance on anode-supported solid oxide fuel cells, wherein the cathode area is smaller than the anode area, is presented. It is shown that the effect of cathode area on cathode polarization, on electrolyte contribution, and on anode resistance, as normalized on the basis of the cathode area, is negligible. There is a small but measurable effect on anode polarization, which results from concentration polarization. Effectively, it is the result of a greater amount of fuel transported to the anode/electrolyte interface in cases wherein the anode area is larger than the cathode area. Experiments were performed on cells made with different cathode areas and geometries. Cathodic and anodic overpotentials measured using reference electrodes, and the measured ohmic area specific resistances by current interruption, were in good agreement with expectations based on the analysis presented. At 800 degreesC, the maximum power density measured with a cathode area of similar to1.1 cm was similar to1.65 W/cm(2) compared to similar to1.45 W/cm(2) for cathode area of similar to2 cm(2), for an anode thickness of similar to1.3 mm, with hydrogen as the fuel and air as-the oxidant. At 750 degreesC, the measured maximum power densities were similar to1.3 W/cm(2) for the cell with a cathode area similar to1.1 cm(2), and similar to1.25 W/cm(2) for the cell with a cathode area similar to2 cm(2). (C) 2001 The Electrochemical Society.