Detection of Radicals by Spin Trapping ESR in a Fuel Cell Operating with a Sulfonated Poly(ether ether ketone) (SPEEK) Membrane

We present experiments in a fuel cell (FC) inserted in the resonator of the electron spin resonance (ESR) spectrometer, which allowed separate monitoring of radical formation at anode and cathode sides. The in situ FC was operated at 300 K under closed- and open-circuit voltage conditions, CCV and OCV, respectively, with a membrane–electrode assembly (MEA) based on sulfonated poly(ether ether ketone) (SPEEK). The formation of radicals was monitored by spin trapping ESR, with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as the spin trap. The magnetic parameters and the relative intensities of DMPO adducts were determined by simulation of the ESR spectra. The major adducts detected at both electrodes were DMPO/OOH and DMPO/H. The generation of the DMPO/OOH adduct at the anode can be explained by reaction of crossover oxygen with hydrogen atoms formed at the Pt catalyst; at the cathode this adduct can be generated by H2 crossover to the cathode, reaction at the Pt catalyst, and reaction with O2. The generation of...