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 in situ, 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.

Nb-doped SrFeO_3−δ (SFO) is used as a cathode in proton-conducting solid oxide fuel cells (H-SOFCs). First-principles calculations show that the SrFe_0.9Nb_0.1O_3−δ (SFNO) cathode has a lower energy barrier in the cathode reaction for H-SOFCs than the Nb-free SrFeO_3−δ cathode. Subsequent experimental studies show that Nb doping substantially enhances the performance of the SrFeO_3−δ cathode. Then, oxygen vacancies (V_O) were introduced into SFNO using the microwave sintering method, further improving the performance of the SFNO cathode. The mechanism behind the performance improvement owing to V_O was revealed using first-principles calculations, with further optimization of the SFNO cathode achieved by developing a suitable wet chemical synthesis route to prepare nanosized SFNO materials. This method significantly reduces the grain size of SFNO compared with the conventional solid-state reaction method, although the solid-state reaction method is generally used for preparing Nb-containing oxides. As a result of defect engineering and synthesis approaches, the SFNO cathode achieved an attractive fuel cell performance, attaining an output of 1764 mW·cm⁻² at 700 °C and operating for more than 200 h. The manipulation of Nb-doped SrFeO_3−δ can be seen as a “one stone, two birds” strategy, enhancing cathode performance while retaining good stability, thus providing an interesting approach for constructing high-performance cathodes for H-SOFCs.