Chemical state identification of Ce3 +/Ce4 + in the Sm0.2Ce0.8O2 − δ electrolyte for an anode-supported solid oxide fuel cell after long-term operation

Direct evidences of cerium valence state transformation from Ce4 + to Ce3 + in an anode-supported solid oxide fuel cell after long-term operation have been identified. Single cell with samarium-doped ceria (Sm0.2Ce0.8O2 − δ, SDC) thin film electrolyte is prepared with maximum power density of 608 mW cm− 2 at 650 °C when the fuel/oxidant flow rates are 335/1005 sccm, respectively. The long-term durability tests are executed by fixed-current operation for 950 h. The power density and voltage degradation are observed and critically attributed to the chemical state transformation of cerium in the electrolyte. From X-ray photoelectron spectroscopy (XPS), the Ce3 + ratio increases from 30.3 to 52.9% in the electrolyte before and after operation. The focused ion beam (FIB)/transmission electron microscopy (TEM) techniques are utilized to investigate the structure variation and the selected area diffraction patterns of the chosen grains towards electrodes identify the phase transformation from CeO2 to Ce2O3, suggesting that the Ce3 + species increase at the near-anode side. The direct evidence of Ce3 + presence shows one of the key factors for the degradation of a low temperature solid oxide fuel cell (LT-SOFC).

The results of XPS curve fitting for the single cell before and after long-term durability test and the fitting contributions of Ce3 + and Ce4 + are displayed in green and red lines. (b) The variation of Ce3 + ratio within the estimated depth of the electrolyte obtained from XPS technique for the single cell after long-term durability test.Figure optionsDownload as PowerPoint slideHighlights
► The SOFC with SDC electrolyte is prepared with performance of 608 mW/cm2 at 650 °C.
► The degradation is partially attributed to chemical state transformation of Ce.
► Ce3 + increase to 52.9% after testing and co-existence of Ce3 +/Ce4 + is confirmed.
► Ce chemical state identification is beneficial for LT-SOFC development.