Mixed proton-electron-oxide ion triple conducting manganite as an efficient cobalt-free cathode for protonic ceramic fuel cells

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2020-01, Vol.8 (21), p.1143-1155
• Main Authors: Wang, Ning, Hinokuma, Satoshi, Ina, Toshiaki, Zhu, Chunyu, Habazaki, Hiroki, Aoki, Yoshitaka
• Format: Article
• Language: English
• Subjects: Cathodes; Cathodic polarization; Chemists; Cobalt; Electrode materials; Electrode polarization; Electrolytes; Electrolytic cells; Fine structure; Fuel cells; Fuel technology; Hydration; Oxygen; Perovskites; Solid oxide fuel cells; Thermogravimetry; Thin films; Ultrastructure; Vacancies; X ray absorption; Zirconium
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d0ta03899g

It is challenging for materials chemists to develop efficient, cobalt-free cathode materials for solid oxide fuel cells mainly because of the resource scarcity. This study demonstrates that a cubic-type La 0.7 Sr 0.3 Mn 0.7 Ni 0.3 O 3− δ (C-LSMN7373) perovskite is promising for intermediate-temperature protonic ceramic fuel cells (PCFCs) because of the sufficient H + /e − /O 2− triple conductivity. The oxide can be hydrated by gaining 0.1 molar fraction of H 2 O under wet air at 415 °C, as confirmed by thermogravimetry analysis. An in situ extended X-ray absorption fine structure (EXAFS) analysis shows that the hydration reaction takes place via the association between H 2 O and oxygen vacancies, coupled with the redox of Mn and O atoms. Rhombohedral-type La 0.7 Sr 0.3 Mn 1− x Ni x O 3− δ cannot undergo hydration because the oxygen vacancy concentration required for water association is lower than the cubic phase concentration. The cathode performances of various PCFCs are examined by fabricating thin-film cells based on a Ba(Zr 0.4 Ce 0.4 Y 0.2 )O 3 electrolyte. The peak power density of the PCFCs with the cubic-type LSMN7373 cathode is 386 mW cm −2 at 600 °C, which is much higher than the reported values for Zr-rich side electrolytes. Moreover, the cathodic polarization resistance is lower than that of a cell with the widely used La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 cathode below 550 °C. Cubic La 0.7 Sr 0.3 Mn 1− x Ni y O 3−δ undergoes the hydration reaction with the charge disproportionation between Mn and O atoms, and thus, can reduce the interfacial polarization of protonic solid oxide cells due to the H + /O 2− /e − triple conductivity.