Effect of serpentine flow-field design on the water management of polymer electrolyte fuel cells: An in-operando neutron radiography study

In-depth understanding of the dynamics of water formation, accumulation and removal is important for flow field design optimization to ensure robust performance and durability of polymer electrolyte fuel cells (PEFCs). Here, in-operando neutron radiography is used to display and quantify liquid water distribution across the entire active area of single-, double- and quad-channel serpentine flow-fields. The results revealed that the water management and performance of PEFCs is strongly affected by the number of serpentine channels in the cathode flow-field. The single-channel serpentine-based PEFC exhibits both a better cell performance and uniformity in the local water distribution. The quad-channel based PEFC exhibits the largest voltage fluctuations caused by severe water flooding in the gas channels. However, the single-channel design leads to significantly larger pressure drop than the multiple-channel counterparts, which requires much higher parasitic power to pressurize and recirculate the reactants. Three different regimes of operation can be defined based on the current density: gradually increasing hydration (< 400 mA cm(-2)), flooding (400 mA cm(-2) <= j <= 600 mA cm(-2)) and drying out (>600 mA cm(-2)). The reduced overall quantity of water in the channels with an increase in current density can be attributed to faster gas velocity and higher cell temperature.