## 3 Materials
### Cathode
To evade this problem a double layered electrolyte composed of gadolinium or samarium doped ceria/YSZ is used [8; 12; 47; 48; 49; 50; 51; 52]. Researcher have explored LSM-YSZ (composite) and LSCF cathodes with YSZ-CGO electrolyte by current over potential measurements and impedance spectroscopy, and it is observed that LSM-YSZ has higher area specific polarization resistance (1.8 \(\Omega\)-cm\({}^{2}\)) as compared to LSCF (0.4 \(\Omega\)-cm\({}^{2}\)) at 850 \({}^{\circ}\)C [51]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Cathode** & \(\sigma_{e}\) (**S**\(\cdot\)**cm\({}^{-1}\))** & \(\sigma_{i}\) (**S**\(\cdot\)**cm\({}^{-1}\))** & **T** (\({}^{\circ}\)**C) \\ \hline LSM & \(<\)200 & \(<\)4 \(\times\) 10\({}^{-8}\) & 800 \\ LSC & 1600 & 0.4 & 800 \\ LSF & \(>\)50 & \(5\times\) 10\({}^{-3}\) & 800 \\ LSCF & 230 & 0.2 & 900 \\ PSF & 300, 78 & - & 550, 800 \\ BSCF & 45, 20 & - & 500, 800 \\ LSCu & 500 & - & 800 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Electronic and Ionic Conductivities of various families of SOFC cathode [8]. Figure 3: Three reaction pathways of oxygen reduction. The solid state reaction that takes place between YSZ electrolyte and MIEC materials during synthesis can be evaded by impregnation of the cathode material into porous electrolyte structure that need low sintering temperature [8; 10; 12; 53]. The impregnation of Perovskite can be obtained by infiltration of aqueous solution molten nitrate salt, or of nitrate salts of ionic species, or suspension of nanoparticle of the material. Similar results are reported by using either of above mention methods [10; 12; 54]. Similar salts can be produced by the above method. For example, [PERSON] _et al._ experimented with the digestion of nitrate solution to produce LSC (La\({}_{0.6}\)Sr\({}_{0.4}\)CoO\({}_{3-\delta}\))-YSZ composite in the form of permeable YSZ disk, and after sintering it at temperature 700 \({}^{\circ}\)C, observed an area specific resistance (ASR) of as small on 0.03 \(\Omega\)-cm\({}^{2}\) at the same 700 \({}^{\circ}\)C [54]. One more way is to use chemically stable perovskite substance having good ionic and electronic flow at lower temperatures. Researchers also studied Pr\({}_{1-x}\)Sr\({}_{x}\)FeO\({}_{3}\) (PSF) group of cathode materials [10; 55]. It was deduced that Pr\({}_{0.8}\)Sr\({}_{0.2}\)FeO\({}_{3}\) perform no solid state reactivity with YSZ and offered area specific polarization reluctance of 0.204 and 0.164 \(\Omega\)-cm\({}^{2}\) respectively at 800 \({}^{\circ}\)C and 850 \({}^{\circ}\)C [55]. Another material that mainly finds application as oxygen separation membrane due its high oxygen surface exchange and diffusion characteristics is Ba\({}_{0.5}\)Sr\({}_{0.5}\)Co\({}_{0.6}\)Fe\({}_{0.4}\)O\({}_{3-5}\) (BSCF) [8; 10; 56]. Both materials (PSF and BSCF) have small electronic conductivity at 800 \({}^{\circ}\)C that enhances with decreasing temperature [57]. Therefore, such substances are useful in low temperature as well as in intermediate temperature SOFC [56; 57; 58; 59]. In comparison, La\({}_{6.4}\)Sr\({}_{1.6}\)Cu\({}_{8}\)O\({}_{20.\pm 8}\) gives very good electrical conductivity but it reacts with YSZ at temperatures above 600 \({}^{\circ}\)C [58]. More information on cathode materials can be accessed through detailed reviews [10; 12; 50; 12].