A novel cathode flow field for PEM fuel cells with alternating depth channels: Under-rib cross flow design and performance assessment

Enhancing under-rib mass transport while reducing pressure-drop penalties remains a key challenge in proton exchange membrane fuel cell (PEMFC) cathode flow-field design. This study proposes an alternating-depth flow field (ADFF), in which neighboring straight channels are periodically arranged with different depths to generate a lateral pressure difference. A three-dimensional steady-state multiphysics model, validated against experimental data obtained with a multi-channel serpentine flow field (MSFF), is employed to compare the ADFF with the MSFF and a straight parallel flow field (SPFF). The numerical results indicate that the ADFF improves oxygen delivery, reduces cathode concentration loss, limits regions of locally high H 2 O concentration, and produces a more uniform current–density distribution. Compared with the MSFF, the ADFF reduces the maximum cathode pressure drop by 85.6 %, while achieving a 3.4 % higher peak power density than the SPFF. Parametric analysis shows that a channel-depth ratio of 1.5 provides the best performance among the investigated cases, while a cathode stoichiometric ratio of 2.5 provides a favorable balance between electrochemical performance and pressure-drop penalty.