Quantitative Evaluations on Ozone Evolution Electrocatalysts by Scanning Electrochemical Microscopy for Oxidative...

This study valorized scanning electrochemical microscopy (SECM) for the detection of dissolved O₃, which is increasingly in demand for water treatment. Au ultramicroelectrodes biased at 0.62 V RHE provided superior activity and selectivity for O₃ reduction, compared to Pt analogues. It allowed quantitative in situ interrogation of ozone evolution reaction (OZER) electrocatalysts with unprecedented estimations on the OZER overpotential. The difference in onset potentials between the OZER and the competing oxygen evolution reaction (OER) primarily accounted for the OZER current efficiency (CE) on boron-doped diamond (BDD, 1.4% at 10 mA cm^-2 in 0.5 M H₂SO₄), Ni-Sb-doped SnO₂ (NSS, 10.8%), and SiO_x-coated NSS (NSS/SiO_x, 34.4%). SECM areal scans in tandem with elemental mapping perspicuously visualized the improved OZER activity by the SiO_x overlayer on NSS. A shift in the charge transfer coefficient further rationalized the elevated OZER selectivity on NSS/SiO_x, in association with the weakened Sn-O bond strength confirmed by valence band X-ray photoelectron spectra. The invigorated OZER on NSS/SiO_x effectively accelerated the degradation of a model aqueous pollutant (4-chlorophenol).