Effect of GDL Structure and Operating Conditions on PEMFC Performance and Liquid Water Removal
Authors: Tateyama Shota , Suzuki Takahiro , Nasu Mitsunori , Hirayama Naoki , Watanabe Masahiro , Uchida Makoto , Iiyama Akihiro , Tsushima Shohji 
Published: December 2024

Proton exchange membrane fuel cells (PEMFCs) are a highly efficient and environmentally friendly energy device that has potential for fuel cell vehicles and other applications due to its low operating temperature and compact size. The PEMFC is assembled by placing a membrane electrode assembly (MEA), which consists of a polymer electrolyte membrane with a catalyst layer and a gas diffusion layer on both sides, between separators.

The GDL is responsible for diffusion of the reaction gas into the catalyst layers, current collection and removal of produced water. Excessive accumulation of produced liquid water within the GDL, known as flooding, inhibits reaction gas feed and causes concentration overpotential. Therefore, clarification of oxygen transport and produced water removal characteristics is essential to improve cell performance.

The objective of this study is to clarify the effects of different GDL structures and operating conditions, such as cell composition, gas flow rate, and humidification conditions, on the liquid water production and removal characteristics and power generation. In this study, the cells with two types of GDLs were prepared and the liquid-water behavior in the MEA and the power generation performance during fuel cell operation under various conditions were investigated using X-ray radiography. Since the effect of GDL structure depends on the cell composition and operating conditions, the GDLs were characterized under the power generation tests of the cell.

PEMFCs with a catalyst layer reaction area and a GDL area of 5×8 mm2 were constructed. Two types of GDL structures were used in the cathode. One was a conventional GDL (SIGRACET®GDL28BC, SGL) and the other was a novel GDL developed by Enomoto Co., Ltd [1-4]. On the other hand, the same GDL (28BC) was used in the anode. The PEMFC was observed with an X-ray imaging system consisting of an X-ray source (TX-9000D, Mars Tohken Solution) and a detector (C15926-01, Hamamatsu Photonics). Hydrogen and air were supplied to the anode and cathode, respectively. The relative humidity of the anode and cathode was 90%. In-situ observation of the liquid water behavior in the PEMFC was performed by taking images in the MEA cross-sectional direction simultaneously with power generation.

Figure 1 shows an X-ray visualization image of liquid water after 800 seconds of power generation at a current density of 0.5 A/cm2 under highly humidified conditions. In this condition, excessive water was produced, causing some of the channels to become plugged with liquid water. The average liquid water thickness of the GDLs under the unblocked channel, indicated by the yellow frame in the figure, was 1.33 mm for the Enomoto GDL and 2.75 mm for the SGL GDL. The result suggests that the liquid water removal property under the operating condition is different depending on the types of GDLs.

Acknowledgments

This work was partially supported by NEDO of Japan through the ECCEED_GDL project.

References

[1] M. Watanabe et al., J. Electrochem. Soc., 166, F3210 (2019).

[2] M. Nasu et al., J. Power Sources, 530, 231251 (2022).

[3] T. Inoue et al., J. Electrochem. Soc., 169, 114504 (2022).

[4] T. Inoue et al., J. Power Sources, 585, 233623 (2023).

Figure 1