Operation of solid oxide fuel cells at reduced temperatures

The fuel cell arrangement La0.6Sr0.4Co0.2Fe0.8O3 / Ce0.9Gd0.1O1.95 / Ni-YSZ, incorporating a dense film (5-10 mu m) of the Ce0.9Gd0.1O1.95 electrolyte tape cast onto the supporting anode, was investigated for intermediate temperature operation (550-650 degrees C). Open circuit voltages of 0.75-0.8 V were obtained at 550-650 degrees C using moist hydrogen as the fuel. These open circuit voltages were consistent with theoretical predictions taking into account the electronic/ionic leakage of the electrolyte film. Power outputs in excess of 125 mW/cm(2) were obtained at 650 degrees C (in excess of 30 mW/cm(2) at 550 degrees C) and the cell resistance was approximately 1 Omega.cm(2) (4 Omega.cm(2) at 550 degrees C). Most of the cell resistance was derived from the cathode according to A.C. impedance measurements and a great deal of effort was spent in testing a double layer cathode structure and a Pd promoted cathode. Hence power outputs in excess of 150 Omega W/cm(2) were obtained at 650 degrees C (in excess of 50 mW/cm(2) at 550 degrees C), although greater improvements were anticipated. Experiments were also carried out at 600 degrees C using direct methanol fuels at the anode, and the maximum power output was approximately half of that obtained with hydrogen. (C) 1999 Elsevier Science Ltd. All rights reserved.