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

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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