Interplay of catalyst corrosion and homogeneous reactive oxygen species in electrochemical ozone production
Electrochemical ozone production (EOP), a six-electron water oxidation, offers potentially sustainable routes for value-added oxidations and disinfectants, but progress in this field is slowed by a dearth in understanding fundamental mechanisms and how to best design improved EOP catalysts. In this work, we combine experimental electrochemistry, spectroscopic detection of reactive oxygen species (ROS), oxygen anion chemical ionization mass spectrometry (CIMS), and computational quantum chemistry calculations to unveil reaction mechanisms and ascertain the key role of corrosion in EOP on nickel and antimony-doped tin oxide (Ni/Sb-SnO2, NATO) electrodes. By comparing experimental potentials with quantum chemistry predictions, hydrogen peroxide is identified as a critical reaction intermediate, and the presence of nickel dopants in NATO catalyzes hydrogen peroxide into solution-phase hydroperoxyl radicals that can be subsequently oxidized into ozone. Isotopic analyses of products show that oxygen atoms in the generated ozone are from both water and the metal oxide lattice. The time evolution of isotopic composition indicates that as NATO catalysts corrode, lattice oxygen is not regenerated. Further analysis suggests that the electrochemical corrosion of tin oxide itself might generate hydrogen peroxide and tin(IV) hydroxide. These implications point to fundamental technological limitations that must be addressed for electrochemical water purification and other future advanced oxidation processes.