Reactive oxygen species formation at Pt nanoparticles revisited by electron paramagnetic resonance and electrochemical analysis

A combined electrochemical and electron paramagnetic resonance (EPR) procedure for the study of oxygen reduction reaction (ORR) intermediates generated at Pt nanoparticles (NPs) is validated in this work. Using spin-trap EPR complemented by electrochemical analysis, we show that we can detect and identify the free radicals that are produced during the ORR through trapping with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) which are otherwise difficult to detect. Experiments with 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO) as spin trap show no evidence of [rad]DEPMPO-OOH and indicate that only [rad]OH radicals are trapped during the ORR. The results of this study serve as a functional proof-of-concept for further research on the identification of radical ORR intermediates in solution. We propose that our procedure can be used for a more rigorous quantification of free radicals involved in other electrochemical reactions.