Research on the mechanism and reaction conditions of electrochemical preparation of persulfate in a split-cell reactor using BDD anode

Abstract

Through a cyclic voltammetry (CV) curve, electron spin resonance spectroscopy (ESR) characterization and a free radical competitive trapping experiment, an analysis was performed on the mechanism of persulfate (PDS) electro-synthesis by sulfate at a boron-doped diamond (BDD) anode. It had been found that there were two pathways of PDS formation. The first was to form PDS through the interaction of sulfate radicals, which were generated from the oxidation reaction mediated by hydroxyl radicals, where the protonized bisulfate ions and sulfuric acid were oxidized by hydroxyl radicals to sulfate radicals. The second was to produce PDS by generating sulfate radicals through the direct loss of electrons from sulfate and bisulfate ions on the electrode surface. In addition, the effects of initial pH, temperature, current density and electrolyte concentration on the synthesis of PDS were investigated in the slotted anode cycle electrolysis mode. As indicated by the results, despite the small effect of the initial pH on PDS synthesis, acidic pH was slightly beneficial to the synthesis of PDS; in electrolysis, the temperature should be controlled below the thermal decomposition temperature of PDS; and in practical application, the increase of impressed current or voltage contributed little to the increase of PDS synthesis concentration and current efficiency. In the case of the impressed current exceeding the limiting current, the adoption of concentrated electrolyte solution shall improve the PDS output and current efficiency.