Session: 01-04-01 Renewable Energy

Paper Number: 132449

132449 - Experimental Study on Water Discharge Characteristics of Pemfc Flow Channel by Superimposing Acoustic Wave 

Polymer electrolyte membrane fuel cells (PEMFCs) have received a large attention in portable power and transportation applications owing to their excellent start-up/shutdown capabilities and low electrical resistance. To prevent the performance degradation in PEMFCs, efficient water management technology which solve the internal flooding problems is essential. The flooding that disturbs oxygen transport to the catalyst layer occurs in all components in PEMFC including the catalyst layer, gas diffusion layer, and flow channel. To prevent flooding problems, most previous studies focused on structural modification and surface wettability modification in both the flow channel and gas diffusion layer. Complex 3D structures can improve performances, but it is difficult to apply to actual PEMFCs. Additionally, although surface wettability modifications holds promise for improving the water management ability of PEMFCs, their efficacy under actual long-term operating conditions has not been verified. Water management in PEMFCs by active control emerges as a more effective approach under actual operating conditions compared to passive control methods.

In this study, in situ experiments were conducted to investigate the effective removal of water generated on the surface of the gas diffusion layer by introducing an acoustic wave (AW) into the flow channel. The experiments were carried out using a unit cell having an active area of 25 cm². For measuring the performance of the PEMFC, the flow rates for hydrogen to the anode and oxygen to the cathode were 1000 mL/min and 375 mL/min, respectively. AWs were generated using a commercial speaker with sin waves superimposed at a frequency of 80 Hz. The sine wave was applied to the speaker using a function generator. The generated AWs were then superimposed on the gas flow supplied to the cathode. When AW was applied to the cathode flows, the performance was improved. The applied AW can help the removal of liquid droplets from gas diffusion layer surfaces in the cathode flow channels. In addition, the high current density during electrochemical reactions produces an excess of water, leading to more pronounced water accumulation resulting more severe mass transport losses. Therefore, the performance improvement by AW was greater at higher current densities.

To investigate the discharge characteristics of liquid-water generated inside the PEMFC, the pressure drop between the cathode inlet and outlet was measured. In typical PEMFCs, two distinct water discharge phenomena occur in the cathode flow channel. The first type involves the periodic release of a large amount of water from the catalyst layer. This occurs when the water saturation level reaches a point where the pressure force is sufficient to overcome the resistance caused by capillary forces in gas diffusion layer pores. The second type is the discharge of small water droplets. This takes place when the remaining water in the gas diffusion layer flows out. In this study, temporal variations of the voltage and pressure were measured under a constant current condition (1 A/cm²) for 6500 seconds. The pressure signals exhibited greater sensitivity compared to the voltage, and the pressure drop followed a similar trend with respect to the cell voltage. This indicates that cell performance was strongly related to the cathode channel's two-phase flows. The large peaks in pressure drops correspond to the first type discharge of accumulated water, while small oscillations occurred when small water droplets during the second type of discharge were being moved. In addition, when the large peaks in pressure drops occurred, there was a sudden increase in cell voltages, representing the removal of flooding. This implies that a more frequent water discharge was required to prevent the flooding. When AW was superimposed to the cathode flows, both water discharge type frequencies increased.

This implies that superimposing AW can help remove liquid droplets from the gas diffusion layer surface in the cathode flow channel. It is expected that the performance and durability of PEMFC can be improved by implementing the flooding prevention method proposed in this study.

Presenting Author: JiYeon Kim Chousn University