Enhanced oxygen exchange kinetics and long-term stability of a Ruddlesden–Popper phase Pr4Ni3O10+δ cathode for solid oxide fuel cells

Abstract

This research explores the intricacies of oxygen exchange kinetics in Pr₄Ni₃O_10+δ (PNO), aiming to assess its potential as a viable cathode material for solid oxide fuel cell applications. Utilizing a multifaceted approach, advanced techniques such as electrical conductivity relaxation, pulse isotopic exchange, and oxygen permeation are employed. A comparative analysis with other promising cathode materials, specifically La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF6428), reveals PNO superior performance. At 650 °C, PNO exhibits a chemical diffusion exchange coefficient, D_chem, and surface exchange coefficient, k_chem, that are an order of magnitude higher than those of LSCF6428. Long-term stability assessment through 1000-h electrical conductivity relaxation testing at 700 °C confirms PNO consistent performance. Oxygen permeation studies reveal an inverse correlation between membrane thickness and the permeation rate. Notably, PNO demonstrates an impressive two-fold higher oxygen flux compared to LSCF6428. Furthermore, PNO maintains stable oxygen permeation over 1000 h at 700 °C, contrasting with an observed 11% degradation in LSCF6428. X-ray diffraction and scanning electron microscopy analyses corroborate PNO stability, while secondary phase formation observed in LSCF6428 contributes to its degradation. The pulse isotopic exchange measurements conducted on the fractionated powder of PNO within the temperature range of 350–450 °C provide valuable insights into the surface exchange mechanism. These measurements reveal that at the highest oxygen partial pressure (pO₂) values covered by the experiments, the relative rates of dissociative adsorption, ℜ_ads, and oxygen incorporation, ℜ_inc, engage in competitive oxygen exchange dynamics. Conversely, at lower pO₂ values, oxygen exchange is predominantly limited by ℜ_ads.