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• Down-the-channel performance model and genetic algorithm are used to optimize flow channel. • The local current density of PEMFC is measured by experiments. • Optimal constant and variable optimal flow channel designs are analyzed. • Optimal variable flow channel designs benefit output performance, especially at low output voltages and large SRCWs. It is necessary to establish an effective method to guide the flow channel design of the bipolar plate (BPP) to obtain the optimal performance of the proton exchange membrane fuel cells (PEMFC). Most of the existing works focused on the optimization of constant channel dimensions and structures without considering achieving the flow channel's optimal local performance. In this study, an approach combining the down-the-channel performance model and genetic algorithm (GA) is developed to optimize BPP channel/rib patterns for fuel cells. A flow channel is divided into several segments, and the channel dimensions of each segment are brought into the down-the-channel performance model as variables to obtain the optimal parameter design by GA. The model and the optimization results are validated by the CFD and local current density experiment. The performance results of both CFD and local current density experiments are in good agreement with the results of the down-the-channel performance model. It is found that the cell performance of variable rib to channel width ratio (RCWR) design along the flow channel is better than the performance of constant RCWR design. Performance improvements are more significant when the sum of rib and channel width (SRCW) is higher, and the output voltage is lower. Smaller SRCW design can effectively reduce the ohmic losses and concentration polarization which is beneficial to cell performance, and as the SRCW is reduced, the performance improvement of variable RCWR design along the flow channel is less necessary. A guide for the design of the cathode flow channel RCWR from upstream to downstream is provided. [Display omitted] [ABSTRACT FROM AUTHOR]