InterPore2026

Observation of Gas and Water Distributions in a Proton Exchange Membrane Water Electrolyzer Using Operando X-ray CT

20 May 2026, 15:20

15m

Oral Presentation (MS10) Advances in imaging porous media: techniques, software and case studies MS10

Speaker

Satoru Kato (TOYOTA Central R&D Labs., Inc.,)

Description

1. Background & Motivation
   　Proton exchange membrane water electrolysis (PEMWE) is recognized as one of the promising options for green hydrogen production. To achieve high current density operation, efficient mass transport within the porous media is essential. While many studies have focused on oxygen gas removal in the anode porous transport layer (PTL), as pointed out in a recent review by Marefati et al. [1], there is a growing concern regarding liquid water accumulation in the cathode gas diffusion layer (GDL). Such the accumulation is suspected to hinder hydrogen discharge and increase hydrogen crossover. Therefore, a comprehensive understanding of the liquid and gas distributions in both the anode and cathode is required. This study aims to visualize the operando 3D distributions of oxygen and water to elucidate the transport phenomena across the membrane electrode assembly (MEA).

2. Experimental Method
   　Operando X-ray CT imaging was performed at SPring-8 BL33XU (Toyota BL) to observe the gas and liquid distributions within a custom-designed PEMWE cell. Titanium paper was used as PTL in the anode and carbon paper was used as GDL on the cathode. The spatial resolution was 3 µm/voxel, and the scan time for each CT acquisition was 2 seconds. Measurements were conducted at room temperature under three applied cell voltages of 1.5 V, 1.75 V, and 2.0 V. Pure water was supplied to the anode during the measurements.

3. Results & Discussion
   　Initial observations before electrolysis showed that the anode titanium paper was almost saturated with water. During electrolysis, the oxygen distribution under the flow channels exhibited a higher concentration near the catalyst layer. This trend agrees with previous literature. However, a distinct phenomenon was observed under the ribs, where the PTL pores were almost entirely filled with oxygen gas. This accumulation under the ribs suggests that rib width, water pressure, and PTL pore characteristics may influence gas evacuation pathways.
   　On the cathode side, no liquid water was detected in the GDL prior to electrolysis. As the applied voltage increased from 1.5 V to 2.0 V, liquid water appeared within the GDL. This is due to the electro-osmotic drag from the anode. Water was first observed under the rib regions, and at higher voltages, separate liquid water regions also appeared under the channel regions. The distribution was notably marble-like across the GDL plane. This suggests that local transport is affected by local variations in the MEA components, such as the structural heterogeneities of the GDL, catalyst layer activity, or membrane characteristics.

4. Conclusion
   　This study demonstrated the operando visualization of gas and water distributions in both anode and cathode porous media. The results suggest the importance of observing the entire MEA to understand the complex water management in PEMWEs. Furthermore, the observed non-uniform distributions in cathode indicate the need for further research into how structural variations contribute to the overall fluid transport in these porous media, providing a foundation for future investigations into mass transport optimization.