Investigation of mass transfer characteristics of PEMFCs alternatively fueled by pure oxygen and air

Proton exchange membrane fuel cells (PEMFCs) have been widely used as power sources for water, land, and air transportation. For underwater scenarios such as underwater vehicles and submarines, the cathode of the PEMFC needs to be alternatively fueled by pure oxygen and air to increase the range on a single refuel. However, the variation of transport and reaction processes within PEMFCs induced by gas reactant alternation between air and pure oxygen remains unclear. Therefore, this study investigates the multi-physics mechanisms of industry-size PEMFCs with an active area of 343 cm2 under alternate-reactant operation conditions. A partially order-reduced algorithm (“3D + 1D” model) is developed to improve model efficiency and accuracy. Under H2-Air fueled mode, the primary losses result from the oxygen transfer, whereas under H2-O2 fueled mode, the primary challenge is the risk of water flooding caused by the higher liquid water saturation. Subsequently, this study investigates the impact of the geometry and operating conditions on PEMFCs' mass transfer characteristics. The results demonstrate that increasing the cathode stoichiometric ratio and the channel/rib ratio can enhance the oxygen transfer of PEMFCs under H2-Air fueled mode and reduce the water flooding risk under H2-O2 fueled mode. Enhancing the degree of flow field refinement can also improve the oxygen transfer of PEMFCs under H2-Air fueled mode. A criterion is proposed to evaluate the performance and efficiency of PEMFCs under the alternate-reactant operation, which can be used to design high-performance, long-range underwater vehicles.