La _{0.5− <i>x</i>}Sc _<i>x</i>Sr _0.5MnO _{3− <i>δ</i>} cathodes for proton-conducting solid oxide fuel cells: Taking advantage of the secondary phase

Abstract

Designing high-performance cathodes is crucial for proton-conducting solid oxide fuel cells (H-SOFCs), as the cathode heavily influences cell performance. Although manganate cathodes exhibit superior stability and thermal compatibility, their poor cathode performance at intermediate temperatures renders them unsuitable for H-SOFC applications. To address this issue, Sc is utilized as a dopant to modify the traditional La_0.5Sr_0.5MnO₃ cathode at the La site. Although the solubility of Sc at the La site is restricted to 2.5%, this modest quantity of Sc doping can improve the material's oxygen and proton transport capabilities, hence improving cathode and fuel cell performance. Furthermore, when the doping concentration exceeds 2.5%, the secondary phase ScMnO₃ forms <i>in situ</i>, resulting in La_0.475Sc_0.025Sr_0.5MnO₃ (LScSM)+ScMnO₃ nanocomposites. Although the secondary phase is often considered undesirable, the high protonation capacity of ScMnO₃ can compensate for the low proton diffusion ability of LScSM. These two phases complement each other to provide high-performance cathodes. The nominal La_0.4Sc_0.1Sr_0.5MnO₃ is the optimal composition, which takes advantage of the excellent electronic conductivity and fast oxygen diffusion rates of LScSM, as well as the good proton diffusion capacity of ScMnO₃, to produce a high fuel cell output of 1529 mW·cm⁻² at 700 °C. Furthermore, the fuel cell exhibited good operational stability under working conditions, indicating that La_0.4Sc_0.1Sr_0.5MnO₃ is a viable cathode choice for H-SOFCs.