New diamond coatings for peroxosulphate production

Abstract

In this work new diamonds coating, named as nanocrystalline diamond (ND) and ultrananocrystalline diamond (UND) are evaluated for the production of peroxospecies derived from the electrolysis of sulphuric acid and their performance is compared to that of a commercial diamond coating widely used in the literature and well-known by its outstanding performance. The oxidant production was tested at two different current densities and significant differences were found in oxidant production between the electrodes applied in the different conditions studied. Results demonstrate that when the lowest current is applied (25 mA cm−2), the ND and UND electrodes are more efficient in the persulfate formation. For ND electrode, this behavior can be explained in terms of the promoted hydroxyl radical formation at these conditions. However, the UND electrode presented different behavior: the lesser hydroxyl formation and highest peroxospecies formation. This behavior may be attributed to the sum of two factors: the high sp2 content in the diamond film and its porosity, that can increase the sulphate adsorption at the surface that, in turn, facilitates the persulfate generation. This behavior can be proved by the Tafel plots and are explained by the electrode’s features discussed by Raman spectra. When the operation current is increased to harsher conditions (300 mA cm−2), the commercial electrode increases importantly the production of the studied oxidant. One more time it can be attributed to the hydroxyl radical generation at this condition. Considering the energy consumption and the process efficiency, it can be concluded that the UND electrode is more attractive for this application in the studied conditions.