Electrolysis of concentrated sulphuric acid In my textbook it is given that for electrolysis of dilute sulfuric acid  at anode following reactions can occur:

At moderate concentrations

$\ce{2H2O -&gt;  O2 + H+ +4 e-}$

And for high concentrations

$\ce{2SO4- -&gt;  S2O8^2- +2 e-}$

SRP value for first reaction is less than second and hence the first reaction should take place. But why does that not hold for high concentrations?
This is because in concentrated sulfuric acid solution equilibrium condition will favour more water molecules than oxidation of water into protons. So there will be an over potential required (to go against the equilibrium) , that is extra potential beyond the theoretical reduction potential derived from thermodynamics to complete the reaction. So the total potential required will be theoretical Plus overpotential. In case of oxidation of sulphate reduction potential will be much less that for water ,thus oxidation of sulphate happens.