A PEFC (polymer electrolyte fuel cell) with a large power generation area of 140 mm × 160 mm has spatial distributions of the water content of the MEA (membrane electrode assembly) and the electric current produced that depend on the flow rate and relative humidity of the supplied gas. When 49 NMR (nuclear magnetic resonance) surface coils arranged in 7 rows × 7 columns were inserted into the PEFC, two-dimensional spatial distributions of the water content of the MEA and the electric current could be measured from the acquired NMR signals. The water content of the MEA was calculated from the intensity of the NMR signal, and the electric current distribution was determined by an inverse analysis that reproduces the spatial distribution of the resonance frequency of the NMR signals. The PEFC, which was supplied with hydrogen and oxygen at a high humidity of 80 %RH, generated electric power at 130 A over the whole area of the MEA. On the other hand, under a low humidity of 40 %RH and low flow rate conditions, the water content of the MEA became high in the midstream and downstream regions, and a high electric current was generated in these regions.
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