On-site H2O2 electrogeneration at a CoS2-based air-diffusion cathode for the electrochemical degradation of organic pollutants

This work reports, for the first time, the manufacture and use of an air-diffusion cathode containing CoS2 nanoparticles to enhance the H2O2 electrogeneration. Hydrothermal synthesis allowed the formation of crystalline CoS2 with pyrite structure, either unsupported or supported on carbon nanotubes. Both kinds of catalysts were characterized by X-ray diffraction and FE-SEM combined with energy dispersive X-ray analysis. The use of carbon nanotubes as support led to a remarkable enhancement of the CoS2 stability, as deduced from cyclic voltammetry analysis. The electrochemical activity of the CoS2-based materials towards the oxygen reduction reaction (ORR) in acidic medium was examined by potentiodynamic techniques using a rotating disk electrode. Both catalysts showed activity towards the ORR, being predominant the two-electron pathway to form H2O2 as main product. A novel CoS2-on-carbon nanotubes catalyzed air-diffusion cathode, as well as an uncatalyzed one made for comparison, was manufactured to electrogenerate H2O2 under galvanostatic conditions in an undivided two-electrode cell. A concentration of 56.9 mM was found with the former cathode at constant j of 100 mA cm-2, much greater than 32.0 mM found with the uncatalyzed cathode. This informs about the high performance of the CoS2 nanoparticles to promote the two-electron ORR. Finally, the treatment of aqueous solutions of the anaesthetic tetracaine at pH 3.0 and 100 mA cm-2 by electro-oxidation and photoelectro-Fenton processes demonstrated the viability of the manufactured CoS2-based cathode for water treatment