Neutron Imaging of Water Accumulation in the Active Area and Channel-to-Manifold Transitions of a PEMFC

Management of liquid water formed by the electrochemical fuel cell reaction is a key factor in PEMFC performance and durability. For practical stack applications, an important consideration is the transport of liquid water at the transition between the ends of the bipolar plate channels and the manifolds, where excess reactant flows from all the individual cells are combined and directed to the stack exhaust. In this region, gas-phase momentum can be very low, especially on the anode, where there is little driving force to remove liquid water that may accumulate as a result of geometrical or surface energy variations, or due to relatively low temperatures that exist outside of the fuel cell active area. This study seeks to characterize the water accumulated within the active area and at the channel-to-manifold transition regions at both the anode and cathode outlets, as a function of cell operating temperature and current density. The neutron imaging method was applied to directly measure the water volumes within the transition regions, and provide a comparison to simultaneously measured water volume within the cell active area. Transition-region water was found to be weakly dependent on current density, suggesting that once water forms in this area, little driving force exists to extract it entirely by means of gas momentum. Moreover, it was found that the active area water volume is strongly dependent on cell temperature, and temperature variation of as little as 0.5 °C can produce a significant change in water accumulation which is reflected in the cell voltage.