Premium
Reaction Kinetics of Hydroxyl Radicals with Model Compounds of Fuel Cell Polymer Membranes
Author(s) -
Dreizler A. M.,
Roduner E.
Publication year - 2012
Publication title -
fuel cells
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.485
H-Index - 69
eISSN - 1615-6854
pISSN - 1615-6846
DOI - 10.1002/fuce.201100157
Subject(s) - chemistry , radical , reaction rate constant , methanesulfonic acid , hydrogen peroxide , membrane , trifluoroacetic acid , kinetics , polymer chemistry , inorganic chemistry , organic chemistry , biochemistry , physics , quantum mechanics
The chemical stability of perfluorinated and non‐perfluorinated low temperature fuel cell model compounds (MCs) against attack by hydroxyl radicals, HO • , is compared using a competition kinetics approach in aqueous solutions at ambient temperature. HO • radicals were generated in situ by UV photolysis of hydrogen peroxide in the electron spin resonance (ESR) resonator. Acetic acid (AA), trifluoroacetic acid (TFAA), methanesulfonic acid (MSA), trifluorosulfonic acid (TFSA), and perfluoro(2‐ethoxyethane)sulfonic acid (PFEESA) were chosen as MCs, while the rate constants of 5,5‐dimethyl‐1‐pyrroline‐ N ‐oxide (DMPO) and methanol (CH 3 OH) served as reference for the determination of relative rate constants by means of steady state ESR signal amplitudes. In decreasing order the rate constants are: k MSA = (4.8 ± 0.2) × 10 7 M –1 s –1 , k AA = (4.2 ± 0.3) × 10 7 M –1 s –1 , k PFEESA = (3.7 ± 0.1) × 10 6 M –1 s –1 , k TFAA = (7.9 ± 0.2) × 10 5 M –1 s –1 , and k TFSA < 1.0 × 10 5 M –1 s –1 . Applying these results to perfluorinated fuel cell membranes like Nafion®, the main points of attack by HO • are concluded to be the ether groups of the side chains, followed by the remaining carboxyl groups from the manufacturing process of the polymers.