# Perspectives on Cathodes for Protonic Ceramic Fuel Cells
## 2 Mixed Proton-Electron-Conducting Cathodes
For BaZrO\({}_{3}\)-based phases, co-doping strategies involving solid solutions, such as BaZr\({}_{0.8-}\)Pr\({}_{x}\)Y\({}_{0.2}\)O\({}_{3-\delta}\)[26] and BaZr\({}_{0.9,x}\)Pr\({}_{x}\)Gd\({}_{0.1}\)O\({}_{3-\delta}\)[27], have been employed, and both good chemical stability and mixed conductivity are achieved when a high Zr content is maintained. [PERSON] et al. reported the formation of complete solid solutions between the important electrolyte composition BaZr\({}_{0.7}\)Ce\({}_{0.2}\)Y\({}_{0.1}\)O\({}_{3-\delta}\) and BaPr\({}_{0.9}\)Y\({}_{0.1}\)O\({}_{3-\delta}\)[28; 29], indicating that although the total conductivity of the solid-solution members may be insufficient for a good electrode performance (0.4 S\(\cdot\)cm\({}^{-1}\) for BaZr\({}_{0.175}\)Ce\({}_{0.05}\)Pr\({}_{0.675}\)Y\({}_{0.1}\)O\({}_{3-\delta}\) \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Composition** & **Abbreviation** & **Composition** & **Abbreviation** \\ \hline BaCe\({}_{0.8}\)Gd\({}_{0.2}\)O\({}_{2.9}\) & BCG20 & Ce\({}_{0.5}\)La\({}_{0.5}\)O\({}_{1.75}\) & 50 LDC \\ BaCe\({}_{0.8}\)Sm\({}_{0.2}\)O\({}_{3-\delta}\) & BCS20 & Ce\({}_{0.8}\)Sm\({}_{0.2}\)O\({}_{2-\delta}\) & 20 SDC \\ BaCe\({}_{0.5}\)Sm\({}_{0.1}\)O\({}_{3-\delta}\) & BCS10 & GdBaCo\({}_{0.2}\)O\({}_{5-\delta}\) & GBCO \\ BaCe\({}_{0.8}\)Y\({}_{0.2}\)O\({}_{3-\delta}\) & BCY20 & LaCo\({}_{0.3-\delta}\) & LCO \\ BaCe\({}_{0.8}\)Y\({}_{0.15}\)O\({}_{3-\delta}\) & BCY15 & LaFeO\({}_{3}\) & LF \\ BaCe\({}_{0.9}\)Y\({}_{0.1}\)O\({}_{3-\delta}\) & BCY10 & La\({}_{2}\)NiO\({}_{4\pm\delta}\) & LNO \\ BaCe\({}_{0.9}\)Y\({}_{0.1}\)O\({}_{3-\delta}\) & BCYb10 & LaNi\({}_{0.6}\)Fe\({}_{0.4}\)O\({}_{3-\delta}\) & LNF \\ BaCe\({}_{0.2}\)Zr\({}_{0.7}\)Y\({}_{0.1}\)O\({}_{3-\delta}\) & BCZY72 & La\({}_{0.5}\)Sr\({}_{0.5}\)CoO\({}_{3-\delta}\) & LSC55 \\ BaCe\({}_{0.2}\)Zr\({}_{0.4}\)Y\({}_{0.2}\)O\({}_{3-\delta}\) & BCY24 & La\({}_{0.6}\)Sr\({}_{0.4}\)CoO\({}_{3-\delta}\) & LSC64 \\ BaCe\({}_{0.5}\)Zr\({}_{0.3}\)Y\({}_{0.2}\)O\({}_{3-\delta}\) & BCZY53 & La\({}_{0.6}\)Sr\({}_{0.4}\)CoO\({}_{3-\delta}\) & LSCF \\ BaCe\({}_{0.6}\)Zr\({}_{0.2}\)Y\({}_{0.2}\)O\({}_{3-\delta}\) & BCZY62 & La\({}_{0.75}\)Sr\({}_{0.2}\)Sr\({}_{0.5}\)MnO\({}_{3-\delta}\) & LSCM \\ BaCe\({}_{0.7}\)Zr\({}_{0.1}\)Y\({}_{0.2}\)O\({}_{3-\delta}\) & BCZY71 & La\({}_{0.7}\)Sr\({}_{0.3}\)FeO\({}_{3-\delta}\) & LSF73 \\ BaCe\({}_{0.8}\)Zr\({}_{0.1}\)Y\({}_{0.1}\)O\({}_{3-\delta}\) & BCZY81 & La\({}_{0.8}\)Sr\({}_{0.2}\)FeO\({}_{3-\delta}\) & LSF82 \\ BaCe\({}_{0.4}\)Zr\({}_{0.4}\)Y\({}_{0.1}\)Y\({}_{0.1}\)Y\({}_{0.1}\)O\({}_{3-\delta}\) & BCZYYb4411 & La\({}_{0.5}\)Sr\({}_{0.5}\)MnO\({}_{3-\delta}\) & LSM55 \\ BaCe\({}_{0.7}\)Zr\({}_{0.1}\)Y\({}_{0.1}\)Y\({}_{0.1}\)O\({}_{3-\delta}\) & BCZYYb7111 & La\({}_{0.7}\)Sr\({}_{0.3}\)MnO\({}_{3-\delta}\) & LSM73 \\ Ba\({}_{0.5}\)Sr\({}_{0.5}\)Co\({}_{0.6}\)Fe\({}_{0.2}\)O\({}_{3-\delta}\) & BSCF & La\({}_{0.8}\)Sr\({}_{0.2}\)MnO\({}_{3-\delta}\) & LSM82 \\ BaZr\({}_{0.8}\)Y\({}_{0.5}\) & BZO & NdBa\({}_{0.5}\)Sr\({}_{0.5}\)Co\({}_{1.5}\)Fe\({}_{0.5}\)O\({}_{5+\delta}\) & NBSCF \\ BaZr\({}_{0.8}\)Y\({}_{0.2}\)O\({}_{3-\delta}\) & BZY20 & PrBr\({}_{0.2}\)Co\({}_{0.5+\delta}\) & PBCO \\ BaZr\({}_{0.8}\)Y\({}_{0.15}\)O\({}_{3-\delta}\) & BZY15 & PrBa\({}_{0.5}\)Sr\({}_{0.5}\)Co\({}_{1.5}\)Fe\({}_{0.5}\)O\({}_{5+\delta}\) & PBSCF \\ BaZr\({}_{0.9}\)Y\({}_{0.1}\)O\({}_{3-\delta}\) & BZY10 & Sm\({}_{0.5}\)Sr\({}_{0.5}\)FeO\({}_{3-\delta}\) & SSF \\ Ce\({}_{0.9}\)Gd\({}_{0.1}\)O\({}_{2-\delta}\) & 10 GDC & Sm\({}_{0.5}\)Sr\({}_{0.5}\)CoO\({}_{3-\delta}\) & SSC \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Abbreviations used in the text corresponding to selected, frequently employed compositions. at 900 \({}^{\circ}\)C in oxidizing conditions), such Pr-doped phases with mixed conductivity may be employed in a composite cathode together with a highly conducting phase. The mixed valence states of Fe and Co may also be exploited to enhance electronic conductivity in proton-conducting perovskite oxides [30; 31]. [PERSON] et al.