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The water generation and water transport occurring in a polymer electrolyte fuel cell (PEFC) can be estimated from the current density generated in the PEFC, and the water content in the polymer electrolyte membrane (PEM). In order to measure the spatial distributions and time-dependent changes of current density generated in a PEFC and the water content in a PEM, we have developed an eight-channel nuclear magnetic resonance (NMR) system. To detect a NMR signal from water in a PEM at eight positions, eight small planar RF detection coils of 0.6 mm inside diameter were inserted between the PEM and the gas diffusion layer (GDL) in a PEFC. The local current density generated at the position of the RF detection coil in a PEFC can be calculated from the frequency shift of the obtained NMR signal due to an additional magnetic field induced by the local current density. In addition, the water content in a PEM at the position of the RF detection coil can be calculated by the amplitude of the obtained NMR signal. The time-dependent changes in the spatial distributions were measured at 4 s intervals when the PEFC was operated with supply gas under conditions of fuel gas utilization of 0.67 and relative humidity of the fuel gas of 70%RH. The experimental result showed that the spatial distributions of the local current density and the water content in the PEM within the PEFC both fluctuated with time.

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 fuel gas such as flow rate and humidity. We measured the spatial distribution and time dependent changes of current density in the PEFC and the water content in PEM using Nuclear-Magnetic-Resonance (NMR) sensors in order to determine the effect of humidity and the utilization ratio of fuel gas. Our experimental results showed that the current density was uniformly distributed from the inlet to the outlet of the fuel gas when the flow rate was high and the humidity of the fuel gas was 70 %RH. On the other hand, when the flow rate was low and the humidity of the fuel gas higher (85 %RH), the spatial distribution of current density and water content in the PEM was non-uniform. We determined the relationship between the transfer phenomenon of water in the PEFC and this non-uniformity of water content and current density. In addition, a map illustrating the behavior of water content in the PEM and current density under electric-generating condition of the PEFC was made showing the relationship between relative humidity and utilization ratio of fuel gas supplied to the PEFC.

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