分散溶剂对PEMFC催化层中超薄Nafion离聚物质子传导的影响

质子交换膜燃料电池(PEMFC)商业化应用的瓶颈仍然是贵金属催化剂导致的成本问题。然而，目前对于催化层中纳米尺度全氟磺酸离聚物(以Nafion为代表)薄膜中质子传导的问题研究不足，无法完善三相界面的成型规律，进而指导催化层设计。在催化层浆料制备过程中，分散溶剂对Nafion的分散形态有直接影响，可能对催化层成型后附着在催化剂颗粒表面Nafion薄膜的微观结构有潜在影响，进而影响Nafion薄膜的质子传导能力。因此，在本文中利用分子自组装技术模拟催化层离聚物薄膜的聚集过程，于模型基底上制备厚度精确可控的纳米尺度Nafion薄膜，并通过微观测试表征技术探索并建立纳米尺度Nafion离聚物的微观结构模型，阐明分散溶剂对Nafion薄膜微观结构及质子传导的影响。研究发现Nafion薄膜在纳米尺度下的质子电导率比体相膜的质子电导率低一个数量级，使用介电常数较小的醇类溶剂可以使Nafion薄膜形成更有利于质子传导的微观结构，使Nafion薄膜的质子电导率得到提高。相关研究结果为优化PEMFC催化层结构，改善PEMFC催化层中质子传导问题提供给了依据。

Effects of Dispersion Solvents on Proton Conduction Behavior of Ultrathin Nafion Films in the Catalyst Layers of Proton Exchange Membrane Fuel Cells

Although there has been great progress, the commercialization of proton exchange membrane fuel cells (PEMFCs) is still hindered by high cost due to the use of Pt catalysts. Furthermore, structural improvement of the catalyst layers is limited by inadequate studies of the ultrathin perfluorosulfonic acid ionomer (e.g., Nafion ionomer) film in the catalyst layers. During the preparation of the catalyst ink, the dispersion solvent affects the morphology of Nafion ionomers, which affects the microstructure and proton conduction behavior of the Nafion thin film wrapped on the surface of the catalyst particles after the catalyst layer is formed. To simulate the aggregation of ionomers in the catalyst layer, a self-assembly technology was used to obtain nanoscale Nafion thin films with precise and controllable thickness on a SiO₂ model substrate. The proton conductivity and microstructure of the Nafion thin films were obtained through electrochemical impedance spectroscopy and a series of micro-characterization methods. Furthermore, the relationship between proton conduction behavior within ultrathin Nafion films and colloidal morphology in Nafion solution was studied using different organic solvents. The goal was to explore and establish the microstructure model of nanoscale Nafion thin films through micro-characterization technologies, such as nuclear magnetic resonance and dynamic light scattering. It was found that at the nanoscale, Nafion thin films (~40 nm) result in low proton conductivity; an order of magnitude lower than that of bulk membranes (~10–100 μm). However, replacing iso-propanol with n-butanol (which has a lower dielectric constant) as the dispersion media of the Nafion ionomer improved the proton conductivity of the Nafion thin films. This is because Nafion in solvents with a lower dielectric constant possesses higher main chain solubility and mobility. Thus, Nafion molecules more easily aggregate into large rod-shaped micelles, which is beneficial to the construction of proton conduction channels after the self-assembly process. Furthermore, the electrostatic force between Nafion aggregates and the substrate in solvents with lower dielectric constant is smaller. This means more sulfonic groups are involved in the formation of proton conduction channels that in turn improve the proton conductivity of the Nafion thin film. In general, Nafion in solvents with lower dielectric constant leads to a structure that can facilitate proton conduction. This study provides guidance for optimizing the structure of ultrathin Nafion films and improving the proton conduction in the catalyst layers of PEMFCs.