Tuning the Oxygen Vacancy of the SrSc0.175Nb0.025Co0.8O3-δ Cathode toward Enhanced Oxygen Reduction Reaction for H+-SOFCs by Water Uptake

The cell output performance of proton-conducting solid oxide fuel cells (H+-SOFCs) is still unsatisfactory due to insufficient intrinsic proton conduction in the traditional perovskite oxides. Previously, we found that the introduction of water can activate proton conduction in the cathode part of the SrSc0.175Nb0.025Co0.8O3-delta (SSNC) to enhance its oxygen reduction reaction. To explore the mechanism, we conducted a detailed analysis using X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and a distribution of relaxation times. Studies found that the introduction of water reduced the valence of the Co ion, increased more oxygen vacancies for generation of more proton defects, and thereby accelerated the process of oxygen reduction. The rate-limiting step of SSNC cathode for oxygen reduction reaction process was changed from the charge transfer process to the surface exchange and oxygen ion diffusion by water uptake. The research results may bring new progress to the development of H+-SOFCs.