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  |

 

Visualization of Liquid Water Behaviors in PEFCs by Soft X-ray Radiography

Shohji TSUSHIMA Tokyo Institute of Technology Shuichiro HIRAI Tokyo Institute of Technology

Abstract

Polymer electrolyte fuel cells (PEFCs) are one of the promising candidates for future power sources in on-site power generation and automobile application. For automobile application, high current density operation is needed and then liquid water accumulation by water generation inside the electrode deteriorates cell performance by insufficient reactant gas supply to the electrode. In this article, liquid water distribution and its discharging behaviors in a polymer electrolyte fuel cell was visualized by soft X-ray radiography which offers high sensitivity to detect liquid water in an operating fuel cell due to its large attenuation coefficient of low energy X-ray toward liquid water. A developed soft X-ray system can provide high spatial resolution by applying large geometrical magnification owing to its configuration with a focused X-ray source. A fuel cell for soft X-ray visualization was specially designed and in situ visualization experiments under fuel cell operation inside the soft X-ray apparatus was performed. Soft X-ray visualization enables us to visualize liquid water discharge process with high spatial and temporal resolution. It was revealed that inhomogeneous liquid water distribution was established even inside the hydrophobic microporous layer (MPL) that was inserted for the purpose of water management of the PEFC. Preferential liquid water accumulation and discharge behaviors through micro-cracks in microporous layer (MPL) was disclosed. It was clearly shown that micro-cracks in the fuel cell play an important role as water transport path, indicating that design and control of micro-cracks in the MPL possibly offers spatially-separated liquid water transport path and reactant gas (air) transport path.

Key Words

Polymer Electrolyte Fuel Cell, Water Tranport, In Situ Visualization, Soft X-ray Radiography

Figures

Fig.1 Polymer electrolyte fuel cell designed for soft X-ray visualization.

 

Fig.2 Liquid water discharge behavior through a crack in MPL in an operating PEMFC