Long-term isothermal experiments of soot combustion were performed on Yttria-stabilized Zirconia, an oxygen ionic conductor, at 370,390 and 410 degrees C. At these temperatures, isotopic experiment confirms that mobile YSZ bulk oxygens oxidize soot at the soot/YSZ interface. In parallel, the surface oxygen exchange process replenishes YSZ oxygen atoms. After long-term isothermal experiments, HR-TEM observations reveal that the remaining soot particles form a continuous thin film on some YSZ grains, which inhibits the oxygen potential gradient, then stopping the oxidation process. All these experiments are in good agreement with the proposed fuel-cell type mechanism of soot on YSZ. (C) 2013 Elsevier B.V. All rights reserved.