What happens at the inert anode in an electrolytic cell?
There is oxidized oxygen in water
$$\ce{2 H2O -&gt; 4 H+(aq)  + O2(g) + 4 e-}.$$
$\ce{HSO4-}$ in sulphuric acid solution can get oxidized as well at high current density and therefore high enough anodic potential:
$$\ce{HSO4-(aq) -&gt; S2O8^2-(aq) + 2 H+(aq) + 2 e- }$$
This is the industrial way to produce potassium peroxodisulphate.