Can alumina behave as a solid electrolyte for oxygen ions? Could a cell be constructed with an oxygen cathode and a molten aluminum anode producing more alumina? Would the resulting alumina deposit on the electrolyte? Would it be crystalline?
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Alumina is one of the most abundant compounds on Earth. If it would be also a solid electrolyte for oxygen ions, why in the world would anyone go into the trouble of dealing with the whole $\ce{Y2O3/ZrO2}$ thing? No, alumina doesn't and can't behave like that. Its oxygen ions are held in place pretty tightly.
Some forms of alumina may serve as conductors of $\ce{Na+}$ and similar cations, but that's another story.
answered Oct 9, 2015 at 23:04
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$\begingroup$ You might use use yttria-stabilized zirconia because alumina is a poor ionic conductor. Ice is a proton conductor, but nobody uses it as such. Ionic conductivity increases with temperature. The melting point of alumina is over 2000°C. Are you sure there's no ionic conduction? $\endgroup$– Pence128Oct 9, 2015 at 23:57
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$\begingroup$ Why, there might be some, just not enough to make a real thing out of it. I should have said "If it would be also a good solid electrolyte..." $\endgroup$ Oct 10, 2015 at 0:07
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$\begingroup$ If you read my question carefully, you'll note that I never asked if alumina is a good solid electrolyte, only if it is one. The popularity of zirconia and ceria based electrolytes in SOFCs proves it doesn't make for a practical electrolyte if the intent is to generate electricity. $\endgroup$– Pence128Oct 10, 2015 at 0:29
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$\begingroup$ Hm... that's right. It turns out that in fact I answered another question, albeit somewhat related to yours. Well, let it remain this way. $\endgroup$ Oct 10, 2015 at 0:45