Numerous efforts have been made to solve the basic transport equation that describes a solid-oxide fuel cell (SOFC) with mixed ionic and electronic conductors (MIECs). The open circuit voltage (OCV) is calculated by Wagner's equation. A current (I) - voltage (V) relationship accounting for electrode polarization voltage losses was developed. However, every electrode degrades with time. Thus, I-V calculations considering electrode degradation using Sm-doped ceria (SDC) electrolytes is described. This method is successful in treating electrode degradation with time. However, the unchanged OCV requires new concepts in the evaluation of electrode degradation. Furthermore, new concepts will be necessary to improve the model of Riess. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3581208] All rights reserved.