Stew_PID

It is a quite old topic, but I must say AC electrolysis exists. It was used, and I think it is still used for the preparation of oxide layers on aluminum surfaces. It is called WGX process. You are absolutely right when you say, that the role of anode and cathode was changed periodically, but some chemical changes can not follow this, so some nascent oxygen remains in the solution which oxidizes the surface of the object.