Determination of Electrode Oxygen Transport Kinetics Using Electrochemical Impedance Spectroscopy Combined with Three-Dimensional Microstructure Measurement: Application to Nd₂NiO_4+δ

Oxygen reduction kinetic parameters – oxygen ion diffusion D δ , molar surface exchange rate ℜ O and surface exchange coefficient k – were determined for porous Nd 2 NiO 4+δ solid oxide fuel cell cathodes as a function of temperature and oxygen partial pressure by analyzing electrochemical impedance spectroscopy data using the Adler-Lane-Steele model. Electrode microstructural data used in the model calculations were obtained by three-dimensional focused ion beam-scanning electron microscope tomography. Cathodes were fabricated using Nd 2 NiO 4+δ powder derived from a sol-gel method and were tested as symmetrical cells with LSGM electrolytes. The oxygen surface exchange rate exhibited a power-law dependency with oxygen partial pressure, whereas the oxygen diffusivity values obtained varied only slightly. The present analysis suggests that the O-interstitial diffusion has a bulk transport path, whereas the surface exchange process involves dissociative adsorption on surface sites followed by O-incorporation. For Nd 2 NiO 4+δ at 700°C and 0.2 atm oxygen pressure, D δ = 5.6·10 −8 cm 2 s −1 , ℜ O = 2.5·10 −8 mol·cm −2 s −1 . The present D δ and ℜ O values and their activation energies are slightly different to those previously reported for Nd 2 NiO 4+δ using other measurement methodologies, and lower than typical state-of-the-art Co-rich perovskites. However, the average k δ = 1.0 10 −5 cm·s −1 at 700°C is comparable to those of fast oxygen exchange rate perovskites.