Measurement of time-dependent changes and spatial distributions of current density in PEFC and water-content of PEM using a planer-surface coil as an NMR signal detector (effect of relative humidity and ratio of utilization of fuel gas on water content in PEM)

To increase the electric power density of a polymer electrolyte fuel cell (PEFC), it is necessary to increase current density flowing through the membrane electrode assembly (MEA) in the whole PEFC. And this is controlled by the conditions of the fuel gas such as flow rate and humidity. We measured the spatial distribution and time dependence of changes in water content in the polymer electrolyte membrane (PEM) using Nuclear-Magnetic-Resonance (NMR) sensors in order to determine the influence of humidity and the utilization ratio of fuel gas on water content in PEM. Our experimental results showed that the water content at the outlet of the fuel gas increased with time when the flow rate was low, and this increase was induced by the water produced at the PEM. On the other hand, the water content in the PEM decreased with time when the flow rate was high and the humidity of the fuel gas was 70 %RH. When the humidity of the fuel gas was 85 %RH, we observed that water condensed at the outlet of the fuel gas. And a map illustrating the behavior of water content in PEM was made from the results.