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Durability aspects of polymer electrolyte membrane fuel cells.

机译：聚合物电解质膜燃料电池的耐久性方面。

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In order for the successful adoption of proton exchange membrane (PEM) fuel cell technology, it is imperative that durability is understood, quantified and improved. A number of mechanisms are known to contribute to PEMFC membrane electrode assembly (MEA) performance degradation. In this dissertation, we show, via experiments, some of the various processes that degrade the proton exchange membrane in a PEM fuel cell; and catalyst poisoning due to hydrogen sulfide (H2S) and siloxane.; The effect of humidity on the chemical stability of two types of membranes, [i.e., perfluorosulfonic acid type (PFSA, NafionRTM 112) and biphenyl sulfone hydrocarbon type, (BPSH-35)] was studied by subjecting the MEAs to open-circuit voltage (OCV) decay and potential cycling tests at elevated temperatures and low inlet gas relative humidities. The BPSH-35 membranes showed poor chemical stability in ex situ Fenton tests compared to that of NafionRTM membranes. However, under fuel cell conditions, BPSH-35 MEAs outperformed NafionRTM 112 MEAs in both the OCV decay and potential cycling tests. For both membranes, (i) at a given temperature, membrane degradation was more pronounced at lower humidities and (ii) at a given relative humidity operation, increasing the cell temperature accelerated membrane degradation. Mechanical stability of these two types of membranes was also studied using relative humidity (RH) cycling.; Hydrogen peroxide (H2O2) formation rates in a proton exchange membrane (PEM) fuel cell were estimated by studying the oxygen reduction reaction (ORR) on a rotating ring disc electrode (RRDE). Fuel cell conditions were replicated by depositing a film of Pt/Vulcan XC-72 catalyst onto the disk and by varying the temperature, dissolved O2 concentration and the acidity levels in HClO4. The HClO4 acidity was correlated to ionomer water activity and hence fuel cell humidity. H 2O2 formation rates showed a linear dependence on oxygen concentration and square dependence on water activity. The H2O 2 selectivity in ORR was independent of oxygen concentration but increased with decrease in water activity (i.e., decreased humidity).; Presences of trace impurities (such as CO, H2S, NH3, etc.) in the fuel also affect PEMFC durability. Among these impurities, H 2S causes significantly higher performance loss and irreversible catalytic poisoning. A concise mechanism for the poisoning kinetics of H2S on composite solid polymer electrolyte Pt (SPE-Pt) electrode was validated experimentally by charge balances and theoretically by a model, which predicted the oxidation current as a function of the applied potential. H2S dissociatively adsorbed onto SPE-Pt electrode as linear and bridge bonded sulfur (S) species and, under favorable potentials, underwent electro-oxidation to sulfur and then to sulfur dioxide (SO2). Fraction of the adsorbed S species remained as 'hard-to-oxidize' adsorbents and caused irreversible loss of catalytic activity. Deactivation of bridge sites occurred first followed by the loss of linear sites. A method to estimate the catalytic sites irreversibly lost due to sulfur poisoning was developed.
机译：为了成功地采用质子交换膜（PEM）燃料电池技术，必须了解，量化和改善耐用性。已知许多机制可导致PEMFC膜电极组件（MEA）性能下降。通过实验，我们展示了降解PEM燃料电池中质子交换膜的各种过程中的一些过程。以及由于硫化氢（H2S）和硅氧烷引起的催化剂中毒。通过将MEAs置于开路电压下，研究了湿度对两种类型膜的化学稳定性的影响，即全氟磺酸型（PFSA，NafionRTM 112）和联苯砜烃型（BPSH-35）]。 （OCV）衰减和在高温和低进气相对湿度下的潜在循环测试。与NafionRTM膜相比，BPSH-35膜在异位Fenton测试中显示出较差的化学稳定性。但是，在燃料电池条件下，BPOC-35 MEA在OCV衰减和潜在循环测试方面均优于NafionRTM 112 MEA。对于两种膜，（i）在给定的温度下，膜的降解在较低的湿度下更加明显，并且（ii）在给定的相对湿度下运行，从而增加了细胞温度，从而加速了膜的降解。还使用相对湿度（RH）循环研究了这两种类型的膜的机械稳定性。通过研究旋转环盘电极（RRDE）上的氧还原反应（ORR）来估计质子交换膜（PEM）燃料电池中的过氧化氢（H2O2）形成速率。通过在圆盘上沉积一层Pt / Vulcan XC-72催化剂膜，并改变温度，溶解的O2浓度和HClO4中的酸度水平，来复制燃料电池的状况。 HClO4的酸度与离聚物的水活度有关，因此与燃料电池的湿度有关。 H 2 O 2的形成速率显示出对氧浓度的线性依赖性和对水活度的平方依赖性。在ORR中H 2 O 2的选择性与氧浓度无关，但随水活度的降低（即湿度降低）而增加。燃料中微量杂质（例如CO，H2S，NH3等）的存在也会影响PEMFC的耐久性。在这些杂质中，H 2S导致明显更高的性能损失和不可逆的催化中毒。通过电荷平衡和理论上的模型，通过实验验证了H2S在复合固体聚合物电解质Pt（SPE-Pt）电极上的中毒动力学的简明机理，该模型预测了氧化电流与施加电势的关系。 H2S以线性和桥键结合的硫（S）形式解离地吸附在SPE-Pt电极上，并在有利的电势下经历了电氧化，氧化成硫，然后氧化成二氧化硫（SO2）。吸附的S物种的馏分仍保留为“难以氧化”的吸附剂，并导致不可逆的催化活性损失。首先发生桥位失活，然后失去线性位。开发了一种估算由于硫中毒而不可逆地损失的催化位点的方法。

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