Investigation of Water Distribution in a Membrane in an Operating PEMFC by Environmental MRI

An environmentally controlled magnetic resonance imaging (MRI) system was developed to investigate the effects of relative humidity (RH) and current density on the transverse water content profile in a membrane under fuel cell operation at a practical fuel cell (PEMFC) operating temperature. The MRI visualization revealed that in a dry condition (40% RH), the water content in the membrane (membrane hydration number, λ) was , and the water content profile was flat because the diffusion process in the membrane was dominant in the water transport. In a standard condition (80% RH), a water content of in the membrane and partial dehydration at the anode were observed at a current density of , indicating that electro-osmosis was influential. In a wet condition (92% RH), a higher water content of around was observed than that at 80% RH, suggesting that the generated water in the cathode catalyst layer was transported to the membrane at 92% RH. A larger water concentration gradient was observed at with 92% RH than that at 80% RH, suggesting that the larger water content in the membrane induced a greater electro-osmotic drag as the electro-osmosis coefficient was positively correlated with the water content.