Characterization of bipolar plate-free polymer electrolyte membrane fuel cells operating in low and high relative humidity

The bipolar plate (BP), a crucial component of the polymer electrolyte membrane fuel cell (PEMFC), has been a significant concern due to its substantial influence on the volume, weight, and cost of the fuel cell electric vehicle (FCEV) stack. Consequently, extensive efforts have been dedicated to resolving this issue. In this study, the performance analysis was conducted by removing either the anode or cathode bipolar plate under varying relative humidity (RH) conditions. Under the An-Ca RH 100% - 100% environment, the peak power density was 0.653 W cm-2 for the conventional cell, 0.715 W cm-2 for the anode BP-free cell, and 1.08 W cm-2 for the cathode BP-free cell. This is due to the improvement in reactant diffusion and the influence of pressure gradients resulting from the removal of the BP. Moreover, the cell without the BP exhibited improved water retention, accentuating its advantages in harsh conditions. In the An-Ca RH 0% - 100% case, the anode BP-free cell demonstrated the highest performance at 0.565 W cm-2, while in the An-Ca RH 100% - 0% case, the cathode BPfree cell showed a performance of 0.830 W cm-2, representing over 300% higher performance compared to the conventional cell.