Effect of current density and sulfuric acid concentration on persulfuric acid generation by boron-doped diamond film anodes

This research investigated the effects of current density and sulfuric acid concentration on the rates of persulfate generation by boron-doped diamond film anodes. Also investigated was the maximum conversion of sulfate to persulfate that could be achieved from electrolysis of sulfuric acid. Experiments were performed in batch systems using a rotating disk electrode (RDE) and a flow-through reactor with parallel plate electrodes. Both the RDE and flow-through experiments showed that there was a linear relationship between persulfate generation rates and current density. Persulfate generation rates became current limited at sulfuric acid concentrations of 2.25 M and above; however, Faradaic efficiencies under current-limited conditions were only ~60 %, and were only weakly dependent on the current density. Persulfate generation rates in the flow-through reactor showed similar dependencies on current density and sulfuric acid concentration as those in the RDE reactor, but were 20-50 % lower. Acid catalyzed and thermal decomposition of persulfate limited the maximum conversion of sulfate to persulfate. A maximum fractional conversion of 78 % was achieved using an initial sulfuric acid concentration of 0.77 M. Surprisingly, this value was independent of the current density over the range of 100-300 mA cm^-2.