Abstract
During the operation of aromatic hydrocarbon-based proton exchange membrane fuel cells, formed radical species attack the membrane. The most deleterious radical formed is HO·, both strongly electrophilic and oxidising. Oligomers of α-methylstyrene sulfonates (PAMSS) were used as model compounds. We report on the complex reaction cascade following the oxidative attack on aromatic cores bearing proton conductive sulfonate groups. UV-absorption bands of initial oxidation products indicate the formation of radical adducts and aromatic cation radicals. Subsequently, a transformation associated with an absorbance build-up at 580 nm is observed, presumably also related to aromatic cation radicals. Build-up and decay are significantly accelerated at high ionic strength levels that are also typical in fuel cells. Increased ionic strength causes phase separation: dynamic light scattering experiments indicate particle formation that is dependent both on chain length and on ionic strength. Aromatic cation radicals are known strong oxidants. With a presumed redox potential of E°((PAMSS-580 nm)·+/PAMSS) ∼ 2 V this oxidizing species should react also with mediocre reductants. Here, Mn(II) was oxidised to Mn(III) with rate constants of (5–10) × 106 M−1s−1. Implications for experimental design of kinetics experiments and understanding chemical mechanisms are discussed.
Funder
Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung
Publisher
The Electrochemical Society
Subject
Materials Chemistry,Electrochemistry,Surfaces, Coatings and Films,Condensed Matter Physics,Renewable Energy, Sustainability and the Environment,Electronic, Optical and Magnetic Materials
Cited by
5 articles.
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