Sr3Fe1.5Zn0.5O7-δ as Cathode for Protonic-Conducting Solid Oxide Fuel Cells with Enhanced Oxygen Reduction Reaction Activity

Abstract

Common concerns about green energy have led to a wide focus on solid oxide fuel cells (SOFCs) for their environmental friendship and high efficiency. As the most popular electrode, perovskite materials feature the flexible structure and abundant oxygen sites, which correspondingly leads to diverse doping strategies and good electrochemical performance. However, the high operating temperature results in hot corrosion of both cells and encapsulating materials. Operating under various atmospheres, the generated impurities also cause a measure of irreversible degradation. Here, we first introduced Zn to Sr3Fe2O7-δ perovskite cathode in protonic ceramic fuel cells (PCFCs). Ruddlesden-Popper oxides Sr3Fe2-xZnxO7-δ (SFZx, x=0, 0.1, 0.5) were successfully synthesized and exhibited great performance under intermediate temperatures. The polarization resistance is 0.072 Ω·cm-2 which is 47% lower than that of the undoped Sr3Fe2O7-δ, and the maximum peak power density of the single-cell of NiO-BaZr0.1Ce0.7Y0.2O3- δ(BZCY)|BZCY|SFZ05 reaches 523.56 mW·cm-2 at 750℃, increased by 22%. The improvement is attributed to the formation of oxygen vacancies and the larger triple-phase boundary areas. Furthermore, the electrochemical impedance spectra (EIS) and distribution of relaxation time (DRT) results manifest that the rate-limiting steps are accelerated charge transfer and ionic migration processes. Finally, SFZ05 also presented better CO2 tolerance under an atmosphere of 5% CO2/air. These results display that SFZ05 is a promising candidate for a highly active and stable cathode for PCFCs.