La_0.5-xSc_xSr_0.5MnO_3-δcathodes for proton-conducting solid oxide fuel cells: Taking advantage of the secondary phase

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 La0.5Sr0.5MnO3 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 in situ, resulting in La0.475Sc0.025Sr0.5MnO3 (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 La0.4Sc0.1Sr0.5MnO3 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<middle dot>cm-2 at 700 degrees C. Furthermore, the fuel cell exhibited good operational stability under working conditions, indicating that La0.4Sc0.1Sr0.5MnO3 is a viable cathode choice for H-SOFCs.