Molecular dynamics study of the effect of wettability of the carbon support on proton transport in Nafion ionomer thin films
Molecular dynamics study of the effect of wettability of the carbon support on proton transport in Nafion ionomer thin films
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DOI：
10.1299/jtst.2016jtst0045
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发表时间：
2016-01-01
影响因子：
1.2
通讯作者：
Tokumasu, Takashi
中科院分区：
文献类型：
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作者：
Aochi, Joji;Mabuchi, Takuya;Tokumasu, Takashi
进行了分子动力学模拟，以阐明用于 Nafion 离聚物薄膜的碳载体的润湿性对离聚物中质子传输的影响，这与聚合物电解质燃料电池的功率密度有关。 Lennard-Jones壁模型用作离聚物的支撑模型，生成两种不同的疏水壁：高疏水壁（H-壁）和低疏水壁（L-壁）。包括 Grotthuss 机制在内的质子输运模型被用来表达真实的质子输运现象（在早期工作中，我们证实它很好地再现了实验测量的 Nafion 膜中的质子自扩散系数。）获得的质子自扩散系数（DH+）表明，H 壁情况下的 DH+ 大于 L 壁情况下的 DH+。这与薄膜的形貌有关。对于H壁情况，形成亲水性Nafion侧链一部分的磺酸基被证实沿膜上侧壁的方向取向，且与膜下侧壁的方向相反，这可以导致Nafion分子排列并在膜中产生层状水结构。还证实，此类水结构具有更好的簇连通性和更大的簇尺寸，这意味着它们可以作为更好的质子传输路径。
Molecular dynamics simulations were carried out to elucidate the effect of the wettability of the carbon support used for Nafion ionomer thin films on proton transport in the ionomer, which is related to the power density of polymer electrolyte fuel cells. The Lennard-Jones wall model was used as the support model for the ionomer to generate two different hydrophobic walls: the high hydrophobic wall (H-wall) and the low hydrophobic wall (L-wall). The proton transport model, including the Grotthuss mechanism, was used to express real proton transport phenomena (In early work, we confirmed that it well reproduces the experimentally measured proton self-diffusion coefficient in a Nafion membrane.) The obtained proton self-diffusion coefficient (DH+) indicated that the DH+ for the H-wall case is larger than for the L-wall case. This is related to the morphology of the films. For the H-wall case, the sulfonic groups that form part of the hydrophilic Nafion side chains were confirmed to be oriented in the direction to the wall in the upper side of the film and opposite from the wall in the lower side of the film, which can lead to the alignment of Nafion molecules and also create lamellar water structures in the film. It was also confirmed that such water structures have better cluster connectivity and larger cluster size, meaning that they serve as better proton transport pathways.