Samarium-doped ceria electrolyt

Fig. 9 (a) Raman spectra obtained from the fractured cross-section of a 4 mm thick Samarium doped Ceria electrolyte pellet exposed to a partial oxygen pressure differential of 4 x 10 and 0.21 atm of the fuel and air sides respectively at 1273 K. Spectra were collected as a function of distance (x) from the fuel side surface. Spectra have been labelled according to x normalised by the total thickness, L, of the pellet, (b) Experimental and theoretical profiles of the P(02) concentration through the electrolyte pellet calculated from the experimental Raman data and a empirical model of the ion diffusion through the pellet. Figure reproduced from reference [63]. 

Di J, Chen M, Wang C, Zheng J, Fan L, Zhu B (2010), Samarium doped ceria-(Li/ Na)2COj composite electrolyte and its electrochemical properties in low temperature solid oxide fuel cell , 7 Power Sources, 195,4695 699. 

It is interesting to see the work by Matsuzaki and Yasuda [18], who investigated Cr poisoning using different combinations of electrolyte and cathodes as electrolyte, they selected YSZ and samarium-doped ceria (SDC), and LSM and LSCF were selected as cathodes. As shown in Fig. 2.5, a potential drop from Cr poisoning is largest and most rapid for LSM/YSZ, whereas LSCF/... 

For a higher conductivity, cerium dioxide can be doped either with gadolinium Cei cGd (02 or with samarium Cex jSmj02 doped cerias are quite stable chemicdly. In solid oxide fuel cells they lack the effect of interactions between the electrolyte and the cathode materials that would lead to the formation of poorly conducting compounds. However, doped cerias have an important defect in that at low oxygen partial pressures (such as those existing close to the anode) they develop a marked electronic conduction. This is entirely inadmissible for the electrolyte, as it leads to internal self-discharge currents and even to a complete internal short circuit. The electronic conduction comes about when Ce" ions in the lattice are partly reduced to Ce " ions, which creates the possibility for electrons to hop between ions of different valency. 

In a search for alternative electrolyte materials (other than YSZ), Dholabhai et al. calculated the ion conductivities of ceria doped with varying fractions of praseodymium, gadolinium, and samarium. Their results were in reasonable agreement with experiments and provide a useful guideline for the future design of ceria-based SOFCs. 

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