Evolution of Water Distribution in PEMFC during On/Off Cycling

The evolution of membrane water concentration profile has been studied by small angle neutron scattering during on/off cycling PEMFC operation with fully humidified air in co-flow configuration. The water concentration profiles during on/off cycling evolve in opposite ways close to the gas inlet and outlet. Whereas the global membrane water content increases at the gas inlet as the fuel cell delivers current, the membranes are dried out at the gas outlet. The balance between the diffusion of water from cathode to anode and the electroosmostic drag from anode to cathode gives a net flow which is different close to the gas inlet and gas outlet. The equilibrium is reached in less than 15?min and it is faster when the fuel cell is switched on that is to say when a proton flows is imposed. Moreoever, the time to equilibrium decreases as the membrane content is increased.