Investigation of a Ba0.5Sr0.5Co0.8Fe0.2O3-δ based cathode IT-SOFC I. The effect of CO2 on the cell performance

A Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) based cathode intermediate temperature solid oxide fuel cell (IT-SOFC) was fabricated and tested. The effect of carbon dioxide on the performance of BSCF cathode was evaluated at temperatures ranging from 450 to 750DGC. The current density was recorded at a constant discharge of voltage value and the electrochemical impedance spectra (EIS) measurements were carried out in the absence and in the presence of CO2 in the oxidant gas line (cathode). It was found that the presence even of relatively small quantities (0.28-3.07%) of CO2 negatively affects the H2-IT-SOFC performance. It was shown that as the CO2 content in the cathode side increases and as the operation temperature decreases, the fuel cell performance is seriously aggravated up to 550 DGC in a reversible way. A further decrease of the operation temperature deteriorates the SOFC performance irreversibly. However, the cell performance can be recovered after treatment at 800DGC in pure oxygen. It was also shown that as the CO2 content increases, the rate of oxygen electrochemical reduction decreases and the corresponding apparent activation energy increases linearly. The EIS results show that the interface resistance increases dramatically after carbon dioxide is added into the oxidant gas line. It is believed that carbon dioxide and temperature, acting in a synergetic way, decrease at least the cathode activity for oxygen reduction. This behaviour could be attributed to the strong carbon dioxide adsorption on the BSCF surface and to the formation of carbonates at temperatures as low as 500 and 450DGC.