The selective reduction of molecular oxygen to superoxide is one of the key reactions in electrochemistry and photocatalysis. Here the effect of Pt co-catalysts, dispersed on titania, either as single atoms or as nanoparticles, on the photocatalytic superoxide (•O2 -) formation in O2 containing solutions is investigated. The •O2 - formation is traced by nitroblue tetrazolium (NBT) assays and in detail by EPR measurements using TEMPO as •O2 - radical scavenger. The results show that the photocatalytic formation rate of •O2 - on titania can strongly be enhanced by using Pt single atoms as a co-catalyst, whereas Pt nanoparticles hardly exhibit any accelerating effect. This finding is of considerable significance regarding photocatalytic degradation and photocatalytic oxidative synthesis processes.

CEET Nanotechnology Centre VŠB Technical University of Ostrava 17 listopadu 2172 15 Ostrava Poruba 70800 Czech Republic

Czech Advanced Technology and Research Institute CATRIN Regional Centre of Advanced Technologies and Materials Palacky University in Olomouc Šlechtitelů 11 Olomouc 78371 Czech Republic

Department of Materials Science and Engineering Chair for Surface Science and Corrosion Friedrich Alexander Universität Erlangen Nürnberg Martensstraße 7 91058 Erlangen Germany

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