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Aluminum really wants to and will form aluminum oxide. Upon research, aluminum oxide is fairly unreactive. I wanted to ask if I had aluminum anode which would quickly form aluminum oxide (which is unreactive), will that inhibit the aluminum from being oxidized? Basically, will aluminum metal loose electrons and become an aluminum ion?

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Aluminum can and is used as both anodes and cathodes in electrochemical cells, but there are some peculiarities to using it as an anode in aqueous solutions. As you note, aluminum forms a passivating oxide layer quite readily, even by exposure to atmosphere. In an aqueous solution, if the potential is high enough, $\ce{OH-}$ and $\ce{O^2-}$ are generated at the anode, which can then react with the aluminum to produce aluminum oxide. $\ce{Al^3+}$ can also be generated directly. The electric field will draw the anions through the growing aluminum oxide layer towards the aluminum surface and the $\ce{Al^3+}$ towards the solution, making the oxide layer grow both away from the electrode surface and into the surface of the electrode. In this way, coatings thicker than the normal passivation in air can be produced. However, aluminum oxide is a good electrical insulator, thus if a dense non-porous layer is grown, it will become impossible to pass current through it and growth will stop, leaving a relatively thin oxide layer (this is how the dielectric layers in electrolytic capacitors are made). This is the normal behaviour in aqueous solutions at near-neutral pH (5–7). [1]

However, if a thick aluminum oxide layer is desired (e.g. to produce coatings on aluminum parts for dying or durability), maintaining porosity is necessary to avoid completely blocking access to the surface. One technique that is commonly used is using a low pH solution, which tends to redissolve some of the oxide and neutralize some of the formed $\ce{OH-}$, leaving pores in the oxide layer through which the ions can travel and continue to react. These pores also give a good structure to retain dyes or lubricants, but generally need to be sealed after to protect against corrosion.

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  • $\begingroup$ ok so is it fair to say that aluminum would not be a good anode material in a cell due to the incapability of not being able to transfer/carry electrons due to the oxide layer $\endgroup$ – user510 Aug 9 '16 at 3:04
  • $\begingroup$ It depends on the specific application and if the potential is low enough, it is possible to avoid significant oxide formation, but you are right that they do not make good anodes in a lot of cases. However, there have been some interesting developments in things like aluminum-air batteries to overcome issues with aluminum anodes. $\endgroup$ – Michael DM Dryden Aug 9 '16 at 5:12
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Very much so. All Aluminum you have ever seen has had a thin layer of aluminum oxide coating it. The outer most layer of aluminum metal instantly oxidizes in air and forms aluminum oxide. This aluminum oxide layer protects the aluminum from further oxidation because the oxygen ions formed are too tightly bound in the matrix to diffuse through to the inner aluminum atoms.

If this layer was permeable to oxygen on a reasonable time scale than the aluminum would degrade rapidly. For example, if mercury is added to aluminum the oxide layer becomes permeable to oxygen and you can watch aluminum break down rapidly.

Youtube vid: https://www.youtube.com/watch?v=Z7Ilxsu-JlY, thanks to Mr. Gray for his video.

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