Since the image is integrated over the neutron path, it does not reveal the local water concentration at a point. Furthermore, a neutron source is not convenient to use. On the other hand, nuclear magnetic resonance (NMR) imaging can acquire a water concentration image as a spatial distribution of water , , , ,  and . However, it is necessary to use a special PEFC
in which the electrodes have many open holes so that electromagnetic waves might penetrate into the PEM  and . Another technique for measuring a NMR image of the water concentration in a PEM by exchanging the electrodes in a PEFC for a RF detector coil has been reported  and . It is difficult Obeticholic Acid solubility dmso to measure a local water concentration in a usual PEFC or a PEFC stack using these techniques. Furthermore, as the acquisition time of NMR imaging is long, this method cannot monitor rapid changes of the water concentration in a PEFC. Flooding causes a reduction in the local electric current density. In order to find the location of low current density in a PEFC, it is useful to measure the spatial distribution of current density, which can be used to estimate the generation rate of water in a PEFC using the relation to which both are proportional . We have developed an eight-channel NMR system which has eight channel parallel transceivers and eight small planar RF detection coils. By
using small planar coils with a 0.6 mm inside diameter, the system can obtain the local water content in a PEM at 1 s intervals because the INK 128 chemical structure usually indispensable phase-encoding operation in NMR imaging is unnecessary . Eight coils inserted at equal intervals from the gas inlet to gas exit in a PEFC can acquire a NMR signal from the water throughout the PEM simultaneously. The spatial distributions of current density and water content in a PEM
can then be calculated from the NMR signal obtained at the eight positions where the coils are placed. This system has the advantage in that the time-dependent change of spatial distributions of current density Oxalosuccinic acid and water content in a PEM can be measured simultaneously in several seconds. This paper describes details of the NMR system, the principles of measurement of the current density and water content in a PEM and the results obtained for the time-dependent change of spatial distributions in a PEFC that is generating electric power. The NMR system developed here consists of eight small planar RF coils, turning circuits, eight channel parallel transceivers and a permanent magnet. Details of each part are described below. The size and shape of the coil were determined from the size of the gas channel and structure of a PEFC. The width of a gas channel used in a usual PEFC is about 1 mm. Hence, the spatial resolution of the water content measurement needs to be smaller than 1 mm.