Investigation of Micro-Porous Layer effect in the Water Distribution in the Polymer Electrolyte Membrane Fuel Cell by Hydrogen-Deuterium Contrast Neutron Radiography

A micro-porous layer (MPL) is commonly applied on the macro-porous layer in a polymer electrolyte fuel cell to provide better electrical contact and mechanical compatibility between layers, and to reduce the flooding related performance loss. However, its fundamental role on water management is still in debate due to the lack of direct visualization evidence. In this study, the role of MPL was investigated by visualizing the change of water distribution through the fuel cell components during operation with high resolution hydrogen-deuterium contrast radiography at the National Institute of Standard and Technology (NIST). Image resolution is approximately at the spatial resolution of 15 μm. Compared to H2O which has high neutron attenuation, D2O is nearly transparent to the neutron beam. In this study, the hydrogen fuel was switched to deuterium after steady state was achieved, and the change of H2O liquid residing in the cell components was observed. Detailed information about how the generated D2O water moves through the diffusion media and the impact of the MPL on the water transport in the cell components was obtained. As shown in Figure 1, it was confirmed that MPL acts as a capillary valve to push the peak of water content in the region between MEA and cathode-side DM into both sides of anode and cathode, resulting in a relatively more flattened water profile through components and thus mitigating flooding. In the talk, the impact of the MPL on water distribution in the fuel cell components, variation of water content in membrane, residual water in the components, and water movement during operation will be discussed. The authors wish to thank Drs. D. Hussey and D. Jacobson for valuable discussions at the NIST imaging facility. A portion of this study was funded by NSF award #CBET0644811.