Ni-Free SOFC Anode Material with Thermal and Redox Stabilities for the Direct Utilization of Ethanol

Abstract

The direct utilization of anhydrous ethanol in solid oxide fuel cells (SOFC), with oxygen-storage anode materials of the type Cu-(ZrxCe1−xY0.2O2−δ-Al2O3), is presented. The ceramic processing of CeO2-Al2O3 and 8YSZ (8% mol yttria stabilized zirconia) favors the reaction between Ceria and 8YSZ. Therefore, anode materials composed of active solid solutions, such as (Zr0.25Ce0.75)0.8Y0.2O1.9 (cubic) and (Zr0.50Ce0.50)0.8Y0.2O1.9 (tetragonal), in addition to the Al2O3 phase, are produced and prevent the formation of CeAlO3. The anodes exhibited an excellent oxygen storage capacity, OSC, between 415 to 446 µmolg−1. This occurred due to the replacement of Ce4+ by Zr4+, generating structural defects that increase the oxygen ion mobility and the activity of the Ce4+/Ce3+ redox pair. The anode material presenting the cubic phase showed a better electrochemical performance. The Al2O3 phase provided thermal stability and prevented the coarsening of the solid solution and loss of Ceria’s redox activity. It allowed for SOFC operation at high temperatures, since the yield increased as the operating temperature rose from 750 to 950 °C. An analysis of the results before and after the SOFC operation at 950 °C for 200 h revealed that there was no significant copper grains coarsening since the performance increased with the temperature. The redox behavior during the SOFC operation is also explained through a theoretical physical–chemical mechanism.