Visualization Of Water Distribution And Removal In The Cathode Of Proton Exchange Membranes Fuel Cells

Water flooding has great influence on the performance, stability and durability of proton exchange membrane fuel cells (PEMFCs). The study of water distribution and removal would be helpful to the understanding of discharging mechanism in fuel cells and give theoretical guidance to the optimization of the flow field and operation style. Therefore, the issue is crucial for the development, application and industrialization of PEMFCs.A transparent PEM single cell with single straight channel in the cathode was designed to study water transportation in the cathode channel. To get the quantified information of the water removal, two parameters - time of the first liquid water discharging and mean interval time between adjacent water dischargings were introduced to further process the channel photos.The combination of visualization technique and pressure-drop monitor was used as the diagnostic tool to detect liquid water in the cathode channels of PEMFCs. The mean fluctuation of pressure-drop was introduced to evaluate the flow channel discharging. It was found that there was a characteristic gas velocity,at which liquid water accumulation in the flow channel was the most. And the amount of maintained water in the channel increased until gas velocity above the critical value. As well as the cause of the phenomena, effects of channel dimension, surface property of the gas diffusion layer, current density anddifferent gas on the characteristic velocity were studied. An empirical expression for the critical velocity was developed and the calculated results were in accord with the experiments.A transparent PEM single cell with 120 cm~2 active area was designed to study water behavior in the straight flow field. The pressure-drop values of different channels proved that uneven reactant distribution was the main cause of the uneven water distribution in the flow field.