Interim-Temperature SOFCs ITSOFCs

The high working temperatures of solid oxide fuel cells, between 900 and 1000°C, lead to numerous problems in the development, manufacture, and practical use of these fuel cells. 

For this reason, the search for solid oxide fuel cells operable at lower temperatures has been primarily via the development of new types of materials for the electrolyte and the electrodes that could work at these temperatures. 

Materials having relatively high ionic (oxide-ion) conductivity in the temperature range considered have been found in numerous studies in the field of 

It can be seen from the figure that, over the temperature range from 1000°C to 400 C, the last two electrolytes have a markedly higher conductivity, than yttria-doped zirconia. It can also be seen from the figure that scandia-doped zirconia has a markedly higher conductivity than yttria-doped zirconia, but it is very rarely used on account of its high price. 

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. 

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