I have use two aluminum pieces as electrodes to electrolys salt (NaCl) water. After the experiment, I found that wherever electricity flows, the electrode will be covered in some blackish substances. One electrode has more dark substances than the other

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Are they Al2O3? Or are they some other substances? Why is one electrode having more and the other having less?

  • $\begingroup$ Alloying in the aluminum, maybe? $\endgroup$ – Oscar Lanzi Dec 29 '19 at 18:10

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