Coupled design of a bamboo-shaped cathode flow field and hybrid-porosity gas diffusion layer for enhanced performance and multiphysics transport in open-cathode PEMFCs

The bamboo-shaped cathode flow field can enhance heat-mass transfer and improve the performance of open-cathode proton exchange membrane fuel cells (PEMFCs). However, its further engineering application faces two prominent challenges: 1) the effects of the key design parameters on cell performance and multiphysics transport remain unclear; 2) geometry-induced local convection enhancement may aggravate the inherent spatial nonuniformity of the physical fields within the porous electrode assembly and increase the risk of local degradation. To address these challenges, this study first studies the impacts of two key design parameters, the number of bamboo-joint units ( N ) and bamboo-joint indentation depth ( W ), on PEMFC performance and the associated heat and mass transfer in porous electrodes. Furthermore, the flow field is coupled with a hybrid-porosity GDL to improve physical field uniformity while retaining enhanced transport. The results show that moderate increases in N and W strengthen the periodic contraction–expansion effect of reactants within the bamboo-shaped configuration, thereby enhancing shear disturbance and lateral mixing. This promotes faster renewal of the thermal and concentration boundary layers in the flow field and porous electrode, thereby increasing the net water and oxygen transport fluxes and improving heat dissipation. Adjusting N and W contributes to superior open-cathode PEMFC performance by up to 8.10 % and 18.85 %, respectively. Increasing N and W also increases the ideal cathode air-supply power due to the relatively larger pressure drop under otherwise identical operating conditions, indicating a greater relative air-supply penalty. Accordingly, the flow field design requires a trade-off among performance improvement, ideal air-supply penalty, and the uniformity of key physical fields within the MEA. Guided by these mechanistic insights, a coupled design is developed by integrating the bamboo-shaped flow field with a hybrid-porosity gas diffusion layer (GDL). This novel design retains the transport and performance advantages of the bamboo-shaped flow field while further alleviating the inherent limitation of the non-uniform distribution of key physical fields within the porous electrode.