Visualization of the oxygen partial pressure (pO(2)) was performed at the surface of a gas diffusion layer (GDL) and the upper part of the gas-flow channel of the cathode of an operating polymer electrolyte fuel cell (PEFC) with straight flow channels by using an oxygen-sensitive luminescent dye film. The gradient of pO(2) inside a channel was clearly observed, even on the GDL surface across the channel. A numerical simulation was performed to understand the reaction distributions inside the PEFC. By visualization and numerical simulation, the distributions of pO(2), the current density, water concentration, and temperature in the operating PEFC were obtained, and the relationships between the parameters were studied. Supersaturated water inside the cell was found both experimentally and computationally. pO(2) and the water concentration were concluded to be the two most important factors in determining the distribution of power generation.
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