Moderation of Oxidative Damage on Aromatic Hydrocarbon-Based Polymers

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 center dot, both strongly electrophilic and oxidising. Oligomers of alpha-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 degrees((PAMSS-580 nm)(+)/PAMSS) similar to 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) x 10(6) M-1 s(-1). Implications for experimental design of kinetics experiments and understanding chemical mechanisms are discussed. (C) 2022 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.

Automated summary

During the operation of aromatic hydrocarbon-based proton exchange membrane fuel cells, radical species attack the membrane. The complex reaction cascade following the oxidative attack on aromatic cores with proton conductive sulfonate groups is reported. High ionic strength levels lead to phase separation and accelerated accumulation and decay processes, which have implications for the design and understanding of fuel cells.