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À propos de : Mechanism of Tetraalkylammonium Headgroup Degradation in Alkaline Fuel CellMembranes        

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  • Mechanism of Tetraalkylammonium Headgroup Degradation in Alkaline Fuel CellMembranes
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  • Cationic headgroups such as tetramethylammonium (TMA) undergo degradation in alkaline conditions throughtwo different mechanisms. In the first mechanism, a hydroxide ion performs an SN2 attack on the methylgroups and directly forms methanol. In the second mechanism, an ylide (trimethylammonium methylide) anda water molecule are formed by the abstraction of a proton from a methyl group. The ylide subsequentlyreacts with water to form methanol. Both pathways have the same overall barrier as observed in our reactionpath calculations with density functional theory. The ylide mechanism is verified by H−D exchange observedbetween the aqueous phase and the cationic head group. We also discuss the effect of the medium and thewater content on the calculated reaction barriers. Good solvation of the head-groups and hydroxide ions isessential for the overall chemical stability of alkaline membranes.
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