## 3 Materials
### Electrolyte
The ionic conductivity of gadolinium doped ceria (CGO-Ce\({}_{0.9}\)Gd\({}_{0.1}\)O\({}_{1.95}\)) electrolyte at 600 \({}^{\circ}\)C is the same as that offered by YSZ at 800 \({}^{\circ}\)C. However, the reduction of Ce\({}^{4+}\) ions to Ce\({}^{3+}\) in CGO results in electron short circuiting due to electronic conduction. This reduction also causes undesirable lattice expansion [10; 35; 63]. It is reported that SOFC with CGO electrolyte can work at lower temperatures of about 500 \({}^{\circ}\)C. In this range of temperature, the contribution of electronic conductivity will be negligible. Also, low temperature ferrite supports components and sealing materials used in this temperature range [10; 35; 63]. Another electrolyte material that has ionic conductivity comparable to CGO is LSGM having a wider ionic window [12; 63]. Despite the fact that LSGM is compelling electrolyte material in intermediate to low temperatures but attaining a single phase and stability are prominent hurdles in using LSGM [10; 12; 35]. LSGM, CeO\({}_{2}\) and Bi\({}_{2}\)O\({}_{3}\) electrolyte are considered fragile for practical devices due to poor mechanical strength [12; 59; 61]. An alternative approach to reduce ohmic losses is to use thin electrolyte in SOFC. The required ionic conductivity can be achieved at temperatures \(<\) 800 \({}^{\circ}\)C if thickness of electrolyte is less than 50 \(\upmu\)m. An electrolyte thickness of 10 to 15 \(\upmu\)m is considered not be diffusible if synthesized by conventional ceramic routes. Ionic conductivity value \(>\) 0.01 S\(\cdot\)cm\({}^{-1}\) can be achieved by this thickness in order to attain area specific resistance below 0.15 \(\Omega\)-cm\({}^{2}\). An electrolyte thickness of 10 to 15 \(\upmu\)m can be obtained by using electrode supported cell with fabrication techniques like electrochemical vapor deposition (EVD), slurry or solution spraying, Sol-gel laser spraying, magnetron sputtering, colloidal deposition _etc._[35; 63]. Both anode and cathode supported cell designs have been under investigation. Other materials having pyrochlore, perovskite and brownmillerite like structures are also explored and evaluated but with limited use in fuel cell [10; 12; 61; 62; 63; 64; 65; 66; 67]. Researchers have observed that the ionic conductivities of different materials not only vary with the varying dopant and its concentration but also with temperature such as the ionic conductivities of 3, 8 and 10 mol % yttria stablized zirconia at 1000 \({}^{\circ}\)C are 0.058 S\(\cdot\)cm\({}^{-1}\), 0.178 S\(\cdot\)cm\({}^{-1}\) and 0.136 S\(\cdot\)cm\({}^{-1}\) respectively, whereas at 800 \({}^{\circ}\)C the observed ionic conductivities are 0.018 S\(\cdot\)cm\({}^{-1}\), 0.052 S\(\cdot\)cm\({}^{-1}\) and 0.037 S\(\cdot\)cm\({}^{-1}\) respectively. Similarly ionic conductivities of 8 and 9 mol % scandia stablized zirconia observed at 1000 \({}^{\circ}\)C are 0.31 S\(\cdot\)cm\({}^{-1}\) and 0.34 S\(\cdot\)cm\({}^{-1}\) respectively whereas at 800 \({}^{\circ}\)C it is 0.12 S\(\cdot\)cm\({}^{-1}\) and 0.109 S\(\cdot\)cm\({}^{-1}\) respectively. The ionic conductivities of electrolytes Ce\({}_{0.8}\)Sm\({}_{0.2}\)O\({}_{1.85}\), Ce\({}_{0.7}\)Gd\({}_{0.3}\)O\({}_{1.85}\) and La\({}_{0.9}\)Sr\({}_{0.1}\)Ga\({}_{0.8}\)Mg\({}_{0.2}\)O\({}_{3-8}\) at 1000 \({}^{\circ}\)C are 0.25 S\(\cdot\)cm\({}^{-1}\), 0.25 S\(\cdot\)cm\({}^{-1}\) and 0.316 S\(\cdot\)cm\({}^{-1}\) respectively, whereas at 800 \({}^{\circ}\)C these were 0.096 S\(\cdot\)cm\({}^{-1}\), 0.093 S\(\cdot\)cm\({}^{-1}\) and 0.121 S\(\cdot\)cm\({}^{-1}\) respectively [8].