Transport phenomena of proton and water in PEFC by MRI and its application to high stability and performance

聚合物电解质燃料电池(PEFC)是一种很有前途的车用电源和现场发电电源。聚合物电解质膜(PEM)是PEFC电堆中最重要的材料之一，它将质子从阳极侧传导到阴极侧，众所周知，其质子导电性取决于其水分含量。这表明质子交换膜中的水与质子传导机制密切相关。在这里，我们演示了通过提供氢(H_2)或氢(D_2)作为燃料来取代电解质膜中的^1H和^2D原子。以氢为燃料，D~(2+)通过氧化反应进入电解膜，被磺酸基团的反离子质子和/或水分子中的氢原子取代。我们用磁共振成像(MRI)测量了氢气切换到重氢供应后H原子分布的变化。磁共振图像清楚地显示…的替代更多的H和D原子发生在阳极侧(燃料供应侧)，D原子取代了电解液膜中几乎所有的H原子。这表明聚合物电解质膜的质子传导机理是“整体机理”，即质子在膜亲水区域的水中的传输是格洛特斯机理，而不是“表面机理”或“车载机理”。为了阐明聚合物电解质燃料电池(PEFC)中GDL的孔结构对水分布和供气露点的影响，采用格子Boltzmann方法计算了由供气通道和多孔气体扩散层组成的PEFC阴极通道中的水蒸气分布。结果表明，GDL的孔隙率对GDL中出现的最大含水率有影响，露点增大，孔隙率减小。另一方面，GDL中的气孔尺寸对PEFC阴极供气的含水率分布及其饱和露点的影响较小。较少

Polymer electrolyte fuel cells (PEFCs) are promising power sources for vehicle applications and on-site power generation. One of the most important materials under development for PEFC stacks is a polymer electrolyte membrane (PEM), which conducts protons the anode to the cathode side, and it is well known that its proton conductivity depends on its water content. It implies that water in a PEM strongly relate to proton conducting mechanism. Here, we demonstrate the ^1H and ^2D atom replace in the electrolyte membrane by supplying hydrogen (H_2) or deuterium (D_2) as the fuel for the PEFC operation. By supplying deuterium as the fuel, D^+ comes into the electrolyte membrane by oxidation reaction, and replace with protons that are counter ion of sulfonic acid group and/or hydrogen atoms of water molecule. We measure the H atom distribution change after switching hydrogen to heavy hydrogen supply by the magnetic resonance imaging (MRI). The MR images clearly show that the replacement of … More the H and D atoms takes place in the anode side (fuel supply side), and D atoms replace almost all H atoms in the electrolyte membrane. This suggests the proton conducting mechanism in the polymer electrolyte membrane is 'bulk mechanism', which protons transport by Grotthuss mechanism in the water of hydrophilic region of the membrane^<7,8>, rather than 'surface mechanism' or 'vehicular mechanism'.Water vapor distribution is a cathode channel of polymer electrolyte fuel cell (PEFC) composed of gas supply channel and porous gas diffusion layer is calculated by lattice Boltzmann method (LBM) in order to clarify effect of porous structure of GDL in PEFC on water distribution and dew point of supplied gas. It is shown that porosity of GDL affects maximum water concentration emerged in the GDL, resulting in increase of dew point with decrease of porosity. On the other hand, pore scale in the GDL is less influential on water concentration distribution and its sesultant dew point of the supplied gas in the cathode of PEFC. Less