Oxygen reduction sites and diffusion paths at La_0.9Sr_0.1MnO_3-x/yttria-stabilized zirconia interface for different cathodic overvoltages by secondary-ion mass spectrometry

Oxygen reduction active sites were investigated at the interface of O₂/La_0.9Sr_0.1MnO_3-x (LSM)/yttria-stabilized zirconia (YSZ) for three different overvoltages of cathodic polarization (η = -0.336 V, η = -0.185 V, and η = -0.090 V versus reference electrode). Isotopic oxygen (¹⁶O/¹⁸O) exchange under cathodic polarization and secondary ion mass spectrometry (SIMS) technique were examined to visualize the oxygen incorporation/reduction active sites. The LSM mesh pattern electrode was prepared to define the area and length of contact between LSM mesh and YSZ. Under cathodic polarization of η = -0.336 V, oxide ions can diffuse through the LSM to take part in the electrode reaction. From the SIMS images of YSZ surface, the active sites for oxygen reduction/incorporation are distributed in spots at the position where the LSM mesh was attached. Especially, O₂/LSM/YSZ three phase boundary (TPB) is the main active site for oxygen incorporation/reduction, although some spots of high ¹⁸O concentration were observed at the center of the LSM mesh part. Under the lower polarization (η = -0.185 V, and η = -0.090 V), oxide ions did not diffuse through the LSM mesh. SIMS imaging analysis of YSZ surface showed high ¹⁸O concentration spots around the center of the LSM mesh part. The distribution of ionic currents at the surface of YSZ affects the distribution of active sites for oxygen incorporation.