In-situ two-phase flow in gas channels of PEMWE

PEMWE (proton exchange membrane water electrolyzer) can operate at a high current density with a small size to obtain a large mount of hydrogen. However, when PEMWE operate under high current density conditions, lots of air bubbles are generated which causes the reduction of water electrolysis efficiency due to the increase of mass transport loss. In this study, three types of flow channels (single serpentine, double serpentine, and parallel) were designed to reduce mass transport loss and PEMWE performances were compared. Among tested channels, the parallel channel had the worst performance because slug flows with Tayler bubbles, that could disturb the water supply, were mainly occurred. Whereas, the single serpentine channel had the best performance because annular flows with a thin liquid film could reduce mass transport loss were dominant.

Related publications

1. S.K. Kim and S.Y. Jung*, “The effect of two-phase flows on PEM water electrolysis cell performance”, Journal of Mechanical Science and Technology 38(8) 3933~3939 (2024) http://doi.org/10.1007/s12206-024-2106-5.

Bubble detachment characteristics in PTL structure of PEMWE observed by in-situ visualization

The structural design of a porous transport layer (PTL) is critical for managing oxygen bubble transport and enhancing the performance of proton exchange membrane water electrolysis (PEMWE). This study systematically investigated the relationship between PTL structural properties, bubble dynamics, and overall cell performance. Through X-ray computed tomography and high-speed imaging, we confirmed that cell performance is determined by gas removal via bubble behavior, rather than by the interface contact resistance. Two gas removal mechanisms governed by the PTL structure were identified. A high-porosity felt PTL exhibited a “dispersed discharge,” where a large number of detachment sites prevent localized gas accumulation. In contrast, a small particle PTL with high hydraulic conductivity exhibited an “active discharge,” which suppresses in-channel slug formation through the energetic and frequent expulsion of bubbles. Both mechanisms effectively mitigate mass transport loss by ensuring a continuous water supply to the catalyst layer. These findings confirmed that high porosity without compromising the electrical conductivity and low throat resistance are the most critical structural parameters for optimizing bubble dynamics. Therefore, for excellent performance in the PEMWE system, a PTL must be designed to maximize the number density of detachment and increase hydraulic conductivity to promote dynamic bubble removal.

Related publications

1. S.K. Kim and S.Y. Jung*, "Effect of porous transport layer structure on bubble behavior in proton exchange membrane water electrolysis." Applied Thermal Engineering, 290, 130177 (2026).

Operando X-ray imaging study on gas transport and discharge behavior across different PTL thickness conditions in PEM water electrolysis

In this study, we investigated how porous transport layer (PTL) thickness influences gas discharge behavior in proton exchange membrane water electrolysis (PEMWE) using in-situ synchrotron X-ray imaging. Titanium felt PTLs with multiple thickness conditions were tested in a custom cell designed for operando visualization, enabling direct observation of gas generation, transport, and removal within the electrode flow field. Our measurements revealed a clear thickness-dependent trend in both electrical loss and gas management. As the PTL became thinner, the electrical pathway tended to improve, which generally reduced ohmic loss. However, when the PTL was reduced beyond a certain level, the performance trend reversed: operando images showed pronounced gas retention beneath the rib region, indicating insufficient in-plane diffusion and delayed discharge of gas pockets. This local gas accumulation can disturb interfacial contact between the PTL and rib and may increase contact resistance and non-uniform current distribution, ultimately degrading overall performance. These results highlight that “thinner is not always better” for PTL design. While reducing thickness can be beneficial for electrical conduction, excessive thinning may compromise gas removal in rib-dominated regions. Therefore, optimizing PTL thickness is essential to minimize localized gas accumulation and ensure stable, uniform operation in PEMWE systems.