Preparation and characterization of a redox-stable Pr0.4Sr0.6Fe0.875Mo0.125O3-δ material as a novel symmetrical electrode for solid oxide cell application

In this work, to simultaneously meet the requirements of good electrochemical performance and redox stability, perovskite oxide Pr0.4Sr0.6Fe0.875Mo0.125O3-δ (PSFM) material has been developed as a novel redox-stable electrode for symmetrical cell application. The experimental results obtained by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy show that metallic Fe nanoparticles will exsolve from the parent oxide PSFM through in-situ exsolution method when treating in 97% H2–3% H2O atmosphere, and then completely re-incorporate into the parent oxide in air, demonstrating excellent redox stability for PSFM material. In addition, the redox stability in electrochemical performance is also studied by recording the electrochemical impedance spectra and distribution of relaxation times (DRT) analysis. It is demonstrated that a constant electrode polarization resistance (Rp) of ~0.60 Ωcm2 is achieved for the symmetrical cell with PSFM electrode in air at 800 °C after activation, and Rp value is significantly increased to 1.59 Ωcm2 when exposing the symmetrical cell to 97% H2–3% H2O, which is possibly ascribed to the significantly decreased electrical conductivity form 71.0 Scm−1in air to 3.8 Scm−1 in 97% H2–3% H2O. Moreover, it is shown that Rp value recorded in air is effectively decreased to ~0.33 Ωcm2, and keeps constant during the following 200-h redox stability testing, while Rp value measured in 97% H2–3% H2O atmosphere is gradually decreased to 0.82 Ωcm2, which can be explained by the enhanced electro-catalytic properties of PSFM electrode induced by the gradually exsolved Fe nanocatalysts from parent PSFM electrode. At the same time, DRT analysis demonstrates that the sub-electrode process including oxygen/hydrogen adsorption, dissociation ionization and surface diffusion to triple phase boundaries occurred at the electrode/electrolyte interfacial is the predominant rate-limiting step, which can be effectively accelerated by surface modification and exsolved Fe nanoparticles. These results indicate that PSFM is a promising symmetrical electrode material for symmetrical cell application because of its good electrochemical performance and excellent long-term redox stability.