Radical (HO•, H• and HOO•) Formation and Ionomer Degradation in Polymer Electrolyte Fuel Cells
Radical (HO•, H• and HOO•) Formation and Ionomer Degradation in Polymer Electrolyte Fuel Cells
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DOI：
10.1149/1.3581040
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发表时间：
2011-01-01
影响因子：
3.9
通讯作者：
Koppenol, Willem H.
中科院分区：
文献类型：
--
作者：
Gubler, Lorenz;Dockheer, Sindy M.;Koppenol, Willem H.
以H2O2为母体分子，污染Fe为参数，模拟了聚合物电解质燃料电池膜上HO中心点、h中心点和HOO中心点自由基的形成及其对全氟烷基磺酸（PFSA）和聚苯乙烯磺酸（PSSA）离子的攻击。在准稳态条件下分析，h中心点的自由基浓度约为10(-19)M， HO中心点为10(-16)M， HOO中心点为10(-10)M。h中心点是由HO中心点与溶解在膜中的H-2反应形成的。假设PFSA离子单体的攻击是通过弱羧基端基进行的。在非原位Fenton试验条件下，计算出的氟化物排放率与实验数据吻合较好。在燃料电池运行条件下，预测的FER被低估了2-3个数量级。在开路电压保持测试期间，很可能由于侧链攻击而导致的退化很普遍。PSSA离聚体的氧化降解遵循完全不同的途径，因为芳香环除了通过HO中心点提取α -氢外，还有效地清除HO中心点形成oh -加合物。后续反应导致链断裂并形成稳定的羟基化降解产物。(C) 2011电化学学会。[DOI: 10.1149/1.3581040]版权所有。
Formation of radicals, such as HO center dot, H-center dot and HOO center dot, in the membrane of the polymer electrolyte fuel cell and their attack on perfluoroalkylsulfonic acid (PFSA) and poly(styrenesulfonic acid) (PSSA) ionomers was simulated based on a kinetic framework with H2O2 as "parent" molecule and with contaminating Fe as parameter. Analysis under quasi-steady state conditions yielded radical concentrations of around 10(-19) M for H-center dot, 10(-16) M for HO center dot and 10(-10) M for HOO center dot. H-center dot is formed via the reaction of HO center dot with H-2 dissolved in the membrane. The attack of the PFSA ionomer was assumed to proceed via weak carboxylic end-groups. The corresponding calculated fluoride emission rate (FER) showed good agreement with experimental data under ex situ Fenton test conditions. The predicted FER under fuel cell operating conditions was underestimated by 2-3 orders of magnitude. It is likely that degradation via side-chain attack is prevalent during open circuit voltage hold tests. The oxidative degradation of PSSA ionomer follows an entirely different pathway, because, in addition to alpha-hydrogen abstraction by HO center dot, the aromatic ring effectively scavenges HO center dot to form an OH-adduct. Follow-up reactions lead to chain scission and formation of a stable hydroxylated degradation product. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3581040] All rights reserved.