The performance of several negative (fuel) and positive (air) electrode compositions for use in reversible solid oxide fuel cells capable of operating both as a fuel cell and as an electrolyzer was investigated in half-cell and full-cell tests. Negative electrode compositions studied were a nickel/zirconia cermet (Ni/YSZ) and lanthanum-substituted strontium titanate/ceria composite, whereas positive electrode compositions examined included mixed ion- and electron-conducting lanthanum strontium ferrite (LSF), lanthanum strontium copper ferrite (LSCuF), lanthanum strontium cobalt ferrite (LSCoF), and lanthanum strontium manganite (LSM). While titanate/ceria and Ni/YSZ electrodes performed similarly in the fuel cell mode in half-cell tests, losses associated with electrolysis were lower for the titanate/ceria electrode. Positive electrodes gave generally higher losses in the electrolysis mode when compared to the fuel cell mode. This behavior was most apparent for mixed-conducting LSCuF and LSCoF electrodes, and discernible but smaller for LSM; observations were consistent with expected trends in the interfacial oxygen vacancy concentration under anodic and cathodic polarization. Full-cell tests conducted for cells with a thin electrolyte (7 mu m YSZ) similarly showed higher polarization losses in the electrolysis than fuel cell direction. (c) 2007 The Electrochemical Society.