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I am told that if electrolysis of dilute sulfuric acid is performed under high charge density, then the following reaction takes place at anode instead of evolving oxygen:

$$\ce{2 HSO4- -> H2S2O8 + 2 e-}$$

Why is that? And can a general conclusion be drawn?

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  • $\begingroup$ High current densities mean high enough applied voltage so the major reaction current is saturated and higher/lower electrode potential is able to perform the next available electrode reaction. $\endgroup$ – Poutnik May 9 at 16:11
  • $\begingroup$ As the voltage increases it may exceed the decomposition potential for other reactions to occur. If these reactions are kinetically favorable they can compete with the initial low potential themodynamically favorable one, see selectivity in parallel youtu.be/oGbht7Jryfo You can calculate Decomposition potentials using the Nernst Equation $\endgroup$ – ChemEng May 10 at 4:00
  • $\begingroup$ Related: Reaction of sulfate ion in copper sulfate electrolysis $\endgroup$ – user7951 May 10 at 16:44

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