Berron Brad J, Faulkner Christopher J, Fischer Remington E, Payne P Andrew, Jennings G Kane
Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, Tennessee 37235, USA.
Langmuir. 2009 Nov 3;25(21):12721-8. doi: 10.1021/la901809f.
The ability to chemically wire ionomer films to electrode surfaces can promote transport near interfaces and impact a host of energy-related applications. Here, we demonstrate proof-of-concept principles for the surface-initiated ring-opening metathesis polymerization (SI-ROMP) of norbornene (NB), 5-butylnorbornene (NBH4), and 5-perfluorobutylnorbornene (NBF4) from Pt-modified gold substrates and the subsequent sulfonation of olefins along the polymer backbones to produce ultrathin sulfonated polymer films. Prior to sulfonation, the films are hydrophobic and exhibit large barriers against ion transport, but sulfonation dramatically reduces the resistance of the films by providing pathways for proton diffusion. Sulfonated films derived from NBF4 and NBH4 yield more anodic potentials for oxygen reduction than those derived from NB or unfunctionalized electrodes. These improvements are consistent with hydrophobic structuring by the fluorocarbon or hydrocarbon side groups to minimize interfacial flooding and generate pathways for enhanced O(2) permeation near the interface. Importantly, we demonstrate that the sulfonated polymer chains remain anchored to the surface during voltammetry for oxygen reduction whereas short-chain thiolates that do not tether polymer are removed from the substrate. This approach, which we extend to unmodified gold electrodes at neutral pH, presents a method of cleaning the ionomer/electrode interface to remove molecular components that may hamper the performance of the electrode.
将离聚物薄膜化学连接到电极表面的能力可以促进界面附近的传输，并影响许多与能源相关的应用。在这里，我们展示了从铂修饰的金基底上进行降冰片烯（NB）、5-丁基降冰片烯（NBH4）和5-全氟丁基降冰片烯（NBF4）的表面引发开环易位聚合（SI-ROMP）以及随后沿聚合物主链对烯烃进行磺化以制备超薄磺化聚合物薄膜的概念验证原理。在磺化之前，薄膜是疏水的，对离子传输表现出很大的阻碍，但磺化通过提供质子扩散途径显著降低了薄膜的电阻。由NBF4和NBH4衍生的磺化薄膜在氧还原方面比由NB或未功能化电极衍生的薄膜产生更正的阳极电位。这些改进与碳氟化合物或烃侧基的疏水结构一致，以最小化界面水淹并在界面附近产生增强O(2)渗透的途径。重要的是，我们证明了在氧还原伏安法期间，磺化聚合物链保持锚定在表面，而未连接聚合物的短链硫醇盐则从基底上被去除。我们将这种方法扩展到中性pH下的未修饰金电极，提出了一种清洁离聚物/电极界面以去除可能阻碍电极性能的分子成分的方法。
