Comparison of Water Transport Mechanisms Between Commercial and Experimental Virgin and Aged Diffusion Media Using High Resolution Neutron Radiography

The motivation of this work is to characterize water transport for a new high tortuosity anode diffusion media (DM) and to provide the modeling community with valuable benchmark validation data. The high resolution neutron images in this work were taken at the Neutron Imaging Facility at the National Institute of Standards and Technology (NIST) Center for Neutron Research. Tests were conducted with well-defined boundary conditions and publically available materials. Gradients in pressure, inlet relative humidity, and temperature were used to isolate hydraulic, diffusion, and temperature driven flow through the membrane and porous media.

A custom designed 4.8 cm²fuel cell with liquid coolant for precise thermal boundary conditions was used to acquire the neutron images. Test conditions were selected to produce extreme gradients within the cell to push model prediction capabilities. The high resolution neutron images allow for the determination of through-plane water profiles and water transfer rates as a function of current density as shown in Figure 1. Additionally, real-time water balance and net water drag measurements were made with dew point sensors.

This talk will discuss the differences in performance and water content of the experimental DM and baseline commercial DM presented previously, and attempt to draw conclusions relating the structural properties of the porous media and resulting performance and water transport and distribution.  Additionally, partially degraded materials (e.g. electrodes used for hundreds of hours) will be compared to virgin materials to understand the impact of age and lifetime on water transport and performance.  Data from this work will build upon an online database of benchmark data for the modeling community made available through this Department of Energy EREE supported program.

Acknowledgements

This work is funded by the United States Department of Energy Efficiency and Renewable Energy (EREE) Program through General Motors under Award Number DE-EE0000470.  The authors would like to thank Dr. Dan Hussy and Dr. David Jacobson of NIST for their guidance.

Figure 1: Liquid water profiles for all 1.5 A/cm² test conditions for baseline DM (upper) and high tortuosity DM (lower). The high tortuosity DM significantly reduces anode water content for identical operating conditions to baseline.