Optical Visualization of Two Phase Flow in PEM Electrolyzers
Polymer electrolyte membrane (PEM) electrolyzers are ideally suited to pairing with renewable energy sources given the capability to operate at high current densities and transition between different potential loading. To become commercially competitive however PEM electrolyzers require improvements in performance and cost reduction. Much of the technology for PEM electrolysis has comes from PEM fuel cells, leaving room for improvement. The slower reaction kinetics and highly corrosive environment at the anode due to the oxygen evolution reaction (OER) in particular requires research and development to increase efficiency. This study focuses on the behavior of two-phase flow of oxygen in water as it relates to cell performance. Optical visualization with a high speed camera was used to observe oxygen bubbles at the anode during PEM electrolysis. Images of oxygen bubbles in two-phase flow were successfully recorded using three experimental setups: a sample holder submerged in a water filled tank, a modified channel-less PEM electrolyzer cell and a modified PEM electrolyzer cell with optically accessible channels. Image processing pathways were successfully developed using MATLAB and Fiji to study individual bubbles in all setups. The channel-less electrolyzer setup operated at a much lower performance than standard PEM electrolyzer cells. It is suspected that contact resistance reduces the electrochemical performance either as a result of the in-plane conductivity for the PTL being very high or large ohmic contact losses where the PTL contacts the current distributor. The optically accessible channel design was able to operate at performances comparable to an unmodified cell and bubble images were captured in-situ to observe bubbly to annular flow regimes over a range of current densities. This investigation showed that flow field channel aspect ratio is an important determinant to cell performance.
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