Ba deficiency is used to tune the electronic, oxygen-ion and proton conduction in BaCo0.4Fe0.4Zr0.1Y0.1O3−δ perovskite for a high-activity cathode of PCFCs.

Protonic ceramic fuel cells (PCFCs) are receiving increasing attention because of their high energy conversion efficiency. However, traditional mixed oxygen-ionic and electronic conductors (MOECs) show sluggish oxygen reduction kinetics when used in PCFCs because of their intrinsic low protonic conductivity. Herein, it is reported that cooperatively regulating the concentration and basicity of oxygen vacancies can result in fast proton transport in MOECs, which is demonstrated in a Zr 4+ -doped Sr 2 Fe 1.5 Mo 0.5 O 6−δ (SFMZ) perovskite. The so-obtained SFMZ perovskite renders plentiful oxygen vacancies and strong hydration ability, which can boost the formation of protonic defects. Furthermore, the chemical diffusion coefficient of protons (D H,chem ) is established first to determine the proton mobility of the cathode. The results indicate that SFMZ exhibits improved proton diffusion kinetics with a D H,chem value of 8.71 × 10 −7 cm 2 s −1 at 700 °C, comparable to the diffusion coefficient of the commonly used protonic electrolyte BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3−δ of 1.84 × 10 −6 cm 2 s −1 . A low polarization resistance of 0.169 Ω cm 2 and a peak power density as high as 0.79 W cm −2 were achieved at 700 °C with the SFMZ cathode. Such excellent performance suggests that rationally tailoring the oxygen vacancy is a feasible strategy to promote proton diffusion in perovskite-structured electrode materials as efficient PCFC cathodes.

Mixed oxygen ionic and electronic conduction is a vital function for cathode materials of solid oxide fuel cells (SOFCs), ensuring high efficiency and low-temperature operation. However, Fe-based layered double perovskites, as a classical family of mixed oxygen ionic and electronic conducting (MIEC) oxides, are generally inactive toward the oxygen reduction reaction due to their intrinsic low electronic and oxygen-ion conductivity. Herein, Zn doping is presented as a novel pathway to improve the electrochemical performance of Fe-based layered double perovskite oxides in SOFC applications. The results demonstrate that the incorporation of Zn ions at Fe sites of the PrBaFe2O5+δ (PBF) lattice simultaneously regulates the concentration of holes and oxygen vacancies. Consequently, the oxygen surface exchange coefficient and oxygen-ion bulk diffusion coefficient of Zn-doped PBF are significantly tuned. The enhanced mixed oxygen ionic and electronic conduction is further confirmed by a lower polarization resistance of 0.0615 and 0.231 Ω·cm2 for PrBaFe1.9Zn0.1O5+δ (PBFZ0.1) and PBF, respectively, which is measured using symmetric cells at 750 °C. Moreover, the PBFZ0.1-based single cell demonstrates the highest output performance among the reported Fe-based layered double perovskite cathodes, rendering a peak power density of 1.06 W·cm–2 at 750 °C and outstanding stability over 240 h at 700 °C. The current work provides a highly effective strategy for designing cathode materials for next-generation SOFCs.

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F-doping promotes the diffusion and surface adsorption process of oxygen at the cathode, and the reaction kinetics have been significantly improved.

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Perovskite oxide Sr2Fe1.3Cu0.2Mo0.5O6−δ (SFCM) is prepared and evaluated as a novel cathode material for solid oxide electrolytic cells (SOECs).