Water behaviour within a proton exchange membrane fuel cell (PEMFC): NMR and MRI studies

PEMFC uses perfluorosulfonic acid membranes (Nafion(R) for example) as solid electrolytes and their performances are strongly dependent on membrane hydration. Therefore, the accurate knowledge of water distribution in the membrane and of the water condensation location in the fuel cell is a fundamental issue. H-1 MRI has been used to study these phenomena into a PEMFC under operation. These experiments, carried out with a whole fuel cell, are more difficult to achieve, because they require a PEMFC free of ferromagnetic species and containing a minimum of paramagnetic materials. Moreover, difficulties arise because of the electric conductance of most of fuel cell components (bipolar plates, backing layers, electrodes). These issues have been addressed and solved by removing the concerned parts (and possibly by replacing them with more appropriate components). This fuel cell proved to have performances comparable to those of commercially available fuel cells. The measurements highlight local inhomogeneities of moisture within the membrane, linked to the geometry of the gas flow channels and to the swelling of Nafion(R).