Newsletter  2012.9  Index

Theme : "Flow in Fuel Cells"   Preface (M. Ogino, M. Oshima, S. Tamano) Visualization of Liquid Water Behaviors in PEFCs by Soft X-ray Radiography Shohji TSUSHIMA, Shuichiro HIRAI (Tokyo Institute of Technology) Measurement and analysis methods of oxygen diffusivity for PEMFC components Norio KUBO, (Fuel Cell Cutting-Edge Research Center, Technology Research Association) Effects of supplied gas humidity change on PEFC transient power generation Takuto ARAKI (Yokohama National University) Numerical simulation and evaluation for developing next generation fuel cells Yuya TACHIKAWA (Kyushu University) Transport Phenomena in Polymer Electrolyte Fuel Cell by Molecular Dynamics Method Takashi TOKUMASU (Tohoku University)   |  Back  |

 

Transport Phenomena in Polymer Electrolyte Fuel Cell by Molecular Dynamics Method

Takashi TOKUMASU Tohoku University

Abstract

In this study, we analyze the nanoscale transport phenomena in polymer electrolyte fuel cell (PEFC) by large scale molecular dynamics (MD) simulations. Figure 1 shows the overall diagram of flow fields in PEFC. We analyze the transport phenomena of proton and water in polymer electrolyte membrane (PEM). A schematic diagram is shown in Fig. 2. In this simulation we obtain the relation between transport phenomena and structure of water in the membrane. The diffusion coefficient of water molecules in PEM is shown in Fig. 3. As shown in this figure, the diffusion coefficient obtained by our simulation is consistent with experimental data. We also analyze the oxygen permeability of ionomer in catalyst layer. A schematic diagram is shown in Fig. 4. From our simulation we obtain the results that the oxygen permeability of ionomer decreases with the increase in the water content, which is the opposite trend from experiment using bulk membrane. More detailed analysis shows that the governing factor to determine the permeability of ionomer is solubility, while it is diffusivity in the case of bulk membrane. At last we analyze the transport phenomena of water droplet in a nano pore. A schematic diagram is shown in Fig. 5. Using this simulation, we analyze the effect of pore size on the force acting on the water droplet from the wall. Using these molecular dynamics simulations, more accurate data and detailed information can be obtained and therefore these techniques lead us to develop higher performance fuel cell for the next generation.

Key Words

Molecular Dynamics Simulation, Transport Phenomena, Water Cluster,Polymer Electrolyte Fuel Cell

Figures

Fig. 1: Molecular dynamics simulations of transport phenomena in Polymer Electrolyte Fuel Cell (PEFC). There are many flow fields which are governed by nanoscale transport phenomena in PEFC and molecular dynamics is a very powerful scheme to analyze these flow fields.

 

Fig. 2: A schematic diagram of transport phenomena of proton and water in polymer electrolyte membrane (PEM) by large scale molecular dynamics simulation. This figure shows that water molecules (red and white) don't distribute uniformly in PEM (green).

 

Fig. 3: Diffusion coefficient of water molecule in PEM against water content. This figure shows that the results obtained in our simulation are consistent with the experimental data.

 

Fig. 4: A schematic diagram of oxygen permeation of ionomer in catalyst layer by large scale molecular dynamics simulation. Oxygen molecules (red) permeate ionomer (green and blue) and reach to a catalyst surface (silver).

 

Fig. 5: A schematic diagram of transport phenomena of water droplet in a nano pore. In this simulation the effect of the size of nano pore on the force acting on the water droplet from the wall is analyzed.