Investigation of water molecule concentration distribution and transport coefficient in solid polymer electrolyte membrane by magnetic resonance imaging

The performance of electrochemical cells, such as fuel cells, which use solid polymer membranes as electrolytes, is strongly dependent on the water molecule concentration in the membrane. Hence, it is important to understand the transport mechanism and concentration distribution of water molecules in the solid polymer electrolyte (SPE) membrane. In this study, the concentration distribution of water molecules and its time evolution in the SPE membrane were measured by magnetic resonance imaging with 100μm space and 15 s time resolutions. In the experiment in which the moistened membrane was taken to be the initial state, the diffusion coefficient of water molecules in the SPE membrane was estimated to be 0.8 × 10^-10 m²/s. In the experiment in which the dried membrane was taken to be the initial state, the fast transport of water molecules, which seems to be caused by the advection effect, was observed, and its equivalent diffusion coefficient was estimated to be 5 × 10^-10 m²/s.