Sensors and Electrochemical Devices Group, Materials Physics and Applications Division, MPA-11, MS D429, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
J Am Chem Soc. 2009 Dec 23;131(50):18096-104. doi: 10.1021/ja9033928.
Neutron reflectometry was used to examine the interactions of polymer electrolyte fuel cell (PEFC) materials that comprise the triple-phase interface. Smooth, idealized layers of Nafion on glassy carbon (GC) and Pt surfaces were used to experimentally model the PEFC electrode interfaces. Different multilayer structures of Nafion were found in contact with the Pt or GC surfaces. These structures showed separate hydrophobic and hydrophilic domains formed within the Nafion layer when equilibrated with saturated D(2)O vapor. A hydrophobic Nafion region was formed adjacent to a Pt film. However, when Nafion was in contact with a PtO surface, the Nafion at the Pt interface became hydrophilic. The adsorbed oxide layer caused a long-range restructuring of the perfluorosulfonic acid polymer chains that comprise Nafion. The thicknesses of the hydrophobic and hydrophilic domains changed to the same magnitude when the oxide layer was present compared to a thin hydrophobic domain in contact with Pt. A three-layer Nafion structure was formed when Nafion was in direct contact with GC. The findings in this research are direct experimental evidence that both the interfacial and long-range structural properties of Nafion are affected by the material with which it is in contact. Evidence of physical changes of aged Nafion films was obtained, and the results showed a permanent increase in the thickness of the Nafion film and a decrease in the scattering length density (SLD), which are attributed to irreversible swelling of the Nafion film. The aging also resulted in a decrease in the SLD of the GC substrate, which is likely due to either an increase in surface oxidation of the carbon or loss of carbon mass at the GC surface.
中子反射法被用于研究构成三相界面的聚合物电解质燃料电池（PEFC）材料的相互作用。使用玻璃碳（GC）和 Pt 表面上的光滑、理想化的全氟磺酸膜（Nafion）层来实验模拟 PEFC 电极界面。在与 Pt 或 GC 表面接触时，发现了不同的 Nafion 多层结构。当与饱和 D2O 蒸汽达到平衡时，这些结构在 Nafion 层内显示出形成的单独的疏水和亲水区域。在 Pt 膜附近形成了疏水的 Nafion 区域。然而，当 Nafion 与 PtO 表面接触时，Nafion 在 Pt 界面处变得亲水。吸附的氧化物层导致包含 Nafion 的全氟磺酸聚合物链发生长程重构。与与 Pt 接触的薄疏水域相比，当存在氧化物层时，疏水和亲水域的厚度都发生了相同的变化。当 Nafion 与 GC 直接接触时，形成了三层 Nafion 结构。这项研究的发现是 Nafion 的界面和长程结构特性受到与其接触的材料影响的直接实验证据。获得了老化 Nafion 膜物理变化的证据，结果表明 Nafion 膜的厚度永久性增加，散射长度密度（SLD）降低，这归因于 Nafion 膜的不可逆溶胀。老化还导致 GC 基底的 SLD 降低，这可能是由于碳的表面氧化增加或 GC 表面的碳质量损失。
