Oxygen reduction kinetic parameters - oxygen ion diffusion Dδ, molar surface exchange rate RO and surface exchange coefficient k - were determined for porous Nd2NiO4+d 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 Nd2NiO4+d 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 Nd2NiO4+d at 700°C and 0.2 atm oxygen pressure, Dδ = 5.6 . 10-8 cm2s-1, RO = 2.5 . 10-8 mol . cm-2 s-1. The present Dd and RO values and their activation energies are slightly different to those previously reported for Nd2NiO4+d using other measurement methodologies, and lower than typical state-of-the-art Co-rich perovskites. However, the average kd = 1.0 10-5 cm . s-1 at 700°C is comparable to those of fast oxygen exchange rate perovskites.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry