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

As oxygen bubbles occur in the catalyst layer and discharge through the PTL into the flow channel, PTL structure strongly influences mass transport and cell performance. This study compares four PTLs—mesh, titanium felt, and sintered foams with 30% and 45% porosity—through performance evaluation and in-situ flow visualization. Bubble detachment behavior was quantified using an image-based intensity method, in which each detachment event generated a distinct intensity peak, allowing the extraction of detachment frequency and period. Bubble diameter at the moment of release was measured by applying the Hough transform to bubble edge images. Titanium felt exhibited the highest number density of bubble detachment and the lowest cell voltage, attributed to its higher porosity. In contrast, the 45% porosity sintered PTL, with the highest hydraulic conductivity, showed short detachment periods and relatively larger bubble diameters. Mesh and low-porosity sintered PTLs frequently generated Taylor bubbles that blocked the channel width, promoting gas accumulation and voltage loss. Overall, the results show that PTL structures promoting frequent detachment with minimal channel obstruction are advantageous for improving PEMWE efficiency.