Anodic formation of persulphate using pulsed current

The anodic formation of persulphate by electrolysis of ammonium sulphate solutions has been studied using constant current pulses varying from 4 msec to 10 min in length. For pulses of less than 2 min duration the current efficiency falls off considerably with increasing frequency, and the effect is most marked with the less concentrated ammonium sulphate solutions. It apparently arises because conditions in electrolysis are initially favourable to oxygen evolution, but they change when a certain quantity of electricity has been passed which also causes the anode potential to rise; unless the pulse duration is sufficient for this change to be accomplished, the current efficiency is very low. The change is interpreted as one of double-layer composition and its implications for the mechanism of anodic persulphate formation are considered.