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

Stephan Den Hartog,Mohammad Samanipour,H.Y Vincent Ching,Sabine Van Doorslaer,Tom Breugelmans,Annick Hubin,Jon Ustarroz

doi:10.1016/j.elecom.2020.106878

Abstract

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 DEPMPO-OOH and indicate that only 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.

Highlights

The loss of electrochemical active surface area (EASA) and degra dation of the proton exchange membrane are two major problems plaguing the cost-effectiveness of Pt nanoparticles (NPs) for use as electrocatalysts in proton-exchange membrane fuel cells (PEMFC) [1,2]
Using spintrap electron paramagnetic resonance (EPR) complemented by electrochemical analysis, we show that we can detect and identify the free radicals that are produced during the oxygen reduction reaction (ORR) through trapping with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) which are otherwise difficult to detect
The increase in EPR intensity DI is consistent with the increase in consumed charge Q, as is evident from Fig. 2b, which shows a plot of the charge Q passed during the ORR over time as calculated according to Fig. 1b

Summary

Introduction

The loss of electrochemical active surface area (EASA) and degra dation of the proton exchange membrane are two major problems plaguing the cost-effectiveness of Pt nanoparticles (NPs) for use as electrocatalysts in proton-exchange membrane fuel cells (PEMFC) [1,2]. EPR studies on the ORR or fuel cell membranes typically use 5,5dimethyl-1-pyrroline-N-oxide (DMPO) for trapping, which readily binds to ROS and yields distinctive spectra that allow for easy identification [1,12]

Methods

Results

Conclusion