Visualizing Oxygen Distribution in the Along-the-channel Direction of Polymer Electrolyte Membrane Water Electrolyzers Using X-ray Imaging

We developed an innovative operando X-ray computed tomography (CT) cell to elucidate oxygen content along a 10 cm x 1 cm membrane electrode assembly (MEA) of polymer electrolyte membrane water electrolyzer (PEMWE). The flow field consists of two parallel channels and one land. X-ray CT with an approximate 3 × 2 mm field of view and a 0.65 μm pixel size enabled visualization of the MEA and flow channels in operando PEMWEs. The cell incorporates three observation windows transparent to X-rays, strategically positioned near the inlet, in the middle of the flow channels, and at the outlet. 2D radiography was employed to observe oxygen content in the flow channels at various current densities with a time resolution step size of 5 ms. The use of water stained with NaI allowed observation of cell morphology and steady-state oxygen distribution in the porous transport layers (PTLs). Results indicate higher oxygen content in the PTL under the land compared to channel, indicating oxygen trapping. In both PTLs and channels higher oxygen content was observed at the outlet compared to the inlet. Oxygen was carried with water along the channel resulting in higher oxygen content at the outlet and this translated to higher content in the PTL due to lower water content in the channel near the outlet. A modeling study was conducted to support experimental results.