Mechanism of tetraalkylammonium headgroup degradation in alkaline fuel cell membranes

被引：342

作者：

Chempath, Shaji ^{[1
]}

Einsla, Brian R. ^{[2
]}

Pratt, Lawrence R. ^{[1
]}

Macomber, Clay S. ^{[2
]}

Boncella, James M. ^{[2
]}

Rau, Jonathan A. ^{[2
]}

Pivovar, Bryan S. ^{[2
]}

机构：

[1] Los Alamos Natl Lab, Div Theoret, Los Alamos, NM 87545 USA

[2] Los Alamos Natl Lab, Mat Phys & Applicat Div, Los Alamos, NM 87545 USA

来源：

JOURNAL OF PHYSICAL CHEMISTRY C | 2008年 / 112卷 / 09期

关键词：

D O I：

10.1021/jp7115577

中图分类号：

O64 [物理化学（理论化学）、化学物理学];

学科分类号：

070304 ; 081704 ;

摘要：

Cationic headgroups such as tetramethylammonium (TMA) undergo degradation in alkaline conditions through two different mechanisms. In the first mechanism, a hydroxide. ion performs an S(N)2 attack on the methyl groups and directly forms methanol. In the second mechanism, an ylide (trimethylammonium methylide) and a water molecule are formed by the abstraction of a proton from a methyl group. The ylide subsequently reacts with water to form methanol. Both pathways have the same overall barrier as observed in our reaction path calculations with density functional theory. The ylide mechanism is verified by H-D exchange observed between the aqueous phase and the cationic head group. We also discuss the effect of the medium and the water content on the calculated reaction barriers. Good solvation of the head-groups and hydroxide ions is essential for the overall chemical stability of alkaline membranes.

引用

页码：3179 / 3182

页数：4

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