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I'm trying to understand why in an acidic environment, rust increases. The explanations I have seen so far basically have the following,

"In acidic environments the cathode for the rusting of iron changes to $O_{2(g)}+4H^+ _{(aq)} + 4e^- \rightarrow 2H_2 O_{(l)}$. The anode reaction remains $Fe_{(s)} \rightarrow Fe^{2+} + 2e^-$. The cell value increases as the cathodic process is lower in the electrochemical series, producing a more effective electrochemical cell, accelerating corrosion rate."

Though I don't understand why in acidic environments the cathode reaction changes? These are some of the explanations I've read

  • In normal oxygenated conditions hydronium ions increase the electrode potential of the reduction of oxygen making it a better oxidant.
  • In acidic environments the reduction of oxygen proceeds more rapidly. (This doesn't seem to really explain it)

Question Why in acidic environments does the cathode reaction for the rusting of iron change?

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