A Large-size engineering single layer fuel cell (SLFC) consisting of a nano-structured Li0.4Mg0.3Zn0.3O2-delta/Ce0.8Sm0.2O2-delta (LMZSDC) composite with an active area of 25 cm(2) (6 cm x 6 cm x 0.1 cm) is successfully fabricated. The SLFC is evaluated by testing the cell durability with a time-dependent degradation using an H-2 fuel and an air oxidant at 600 degrees C for over 120 h. A maximum power of 12.8 W (512 mW cm(-2)) is achieved at 600 degrees C. In the initial operation stage around 50 h, the cell's performance decreases from 12.8 to 11.2 W; however, after this point, the performance was consistently stable, and no significant degradation is observed in the current density or the cell performance. The device performed excellently at low temperatures with a delivered power output of more than 250 mW cm(-2) at a temperature as low as 400 degrees C. By curve fitting the X-ray photoelectron spectroscopy (XPS) results, the ratio of Ce3+/(Ce3++Ce4+) before and after the long-time operation is analyzed. The ratio increased from 28.2% to 31.4% in the electrolyte which indicates a reduction occurs in the beginning operation that causes an initial performance loss for the device power output and OCV. Electrochemical impedance analyses indicate that the LMZSDC had a high ionic transport, and the device had quick dynamic processes and, thus, a high fuel cell performance. The LMZSDC is a new type of ionic material that has been successfully applied to SLFCs. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.