Visualization of Liquid Water Distribution in an Operational PEMFC by Soft X-Ray Radiography

Proton exchange membrane fuel cells (PEMFCs) are regarded as a promising alternative clean power source for automobile applications. Key to the acceptance of PEFCs for automobiles is further cost reduction and downsizing of the PEMFC stack are needed. In order to meet these demands, further improvements of cell performance under severe operating condition such as low relative humidity and high current density is required. Under high current density operation, excess water is generated and condenses, filling the pores of electrodes with liquid water and hence limiting the reactant transport to catalyst sites. This phenomenon known as “flooding” is an important limiting factor of PEMFC performance. A fundamental understanding of two-phase transport in porous gas diffusion layers (GDLs) of PEMFCs is essential for improvement of performance. In this study, the effects of the distribution of liquid water on performance[1] were investigated by soft X-ray radiography, because higher contrast originated with water can be expected in soft X-ray range as shown in figure 1.