Time-dependent performance change of single layer fuel cell with Li0.4Mg0.3Zn0.3O/Ce0.8Sm0.2O2−δ composite

•Single layer fuel cell (SLFC) was fabricated for large-size engineering cells.•LMZSDC – a new type ionic conducting material were developed for the SLFCs.•The SLFC is technically useful with a power output of 12.8 W (514 mW cm−2) at 600 °C.•Durability tests were carried out and corresponding mechanism was studied.•The SLFC, would be an optimum for the commercialization.

A Large-size engineering single layer fuel cell (SLFC) consisting of a nano-structured Li0.4Mg0.3Zn0.3O2−δ/Ce0.9Sm0.1O2−δ (LMZSDC) composite with an active area of 25 cm2 (6 cm × 6 cm × 0.1 cm) is successfully fabricated. The SLFC is evaluated by testing the cell durability with a time-dependent degradation using an H2 fuel and an air oxidant at 600 °C for over 120 h. A maximum power of 12.8 W (512 mW cm−2) is achieved at 600 °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 °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.