Design strategies for mainstream flow channels in large-area PEMFC: From typical units to large areas

Developing a large-scale flow field is essential for high-power proton exchange membrane fuel cells. A typical small-scale unit should be expanded to create the mainstream zone of a large-area flow field. This study investigated various design strategies for area magnification through numerical analysis. The impacts of channel length, number of channel branches, scaling factor, and channel/rib ratio on cell performance were thoroughly analyzed. An extraction method for concentration loss was devised to evaluate the primary voltage loss, and a contribution factor was determined. It was found that adding channel branches and proportional amplification led to a performance decline of 4.3 % and 42.6 %, respectively. However, extending channel length can slightly improve the PEMFC power density by 0.5 %–3.4 %. All three area magnification methods affect the bulk concentration in the channel, thereby influencing concentration loss. Moreover, proportional amplification and increasing C/R ratio can also deteriorate the mass transport ability from channel to porous electrode. When adjusting the channel length and C/R ratio, concentration loss is emerged as the primary factor driving performance differences, with a contribution factor exceeding 80 %, significantly higher than the other two voltage losses. However, in the case of altering the number of branches and proportional amplification, ohmic or activation loss also plays a crucial role. The performance of large-area fuel cells will be significantly improved if the area amplification strategy is selected reasonably. Among the three area magnification strategies, adding channel branches is suggested, considering both pump loss and performance degradation. For channel lengths exceeding 100 mm, the pump power density increased exponentially (more than eight times), which is unfavorable. Proportional amplification may lead to a substantial decline (>40 %) in cell output performance.