Measurement of mass transport losses breakdown: The Pulsed Gas Analysis (PGA) method
Mass transport losses represent a significant limitation for the maximal reachable power density of polymer electrolyte fuel cells (PEFCs). The ability to measure them, in order to minimize them, is of high interest for the design of the structure of fuel cell components. Helox/oxygen voltage gain measurement is a known method to evaluate these losses, though its classical application suffers from measurement artifacts due to the different physical properties of helox (a mixture of helium and oxygen) and air in terms of water management, and due to the oxidation of the catalyst surface following extended operation with pure oxygen. Our Pulse Gas Analysis (PGA) method  solves both issues by operating the cell most of the time with air on the cathode and using short periods of operation (typically 1 second) with helox or oxygen. An optimized in house developed fuel cell test stand ensures a fast, seamless switching between the gases.
|Bulk diffusion is the dominating diffusion mode in pores much larger than the mean free path of the gas molecules (~50 nm). The oxygen transport is limited by collisions with nitrogen molecules.||x||x||x||Helox gain|
|Knudsen diffusion is the dominating diffusion mode in pores much smaller than the mean free path of the gas molecules. The oxygen transport is limited by collisions with the material structure.||x||x||Oxygen gain|
|Thin film diffusion is represents the transport of oxygen to catalyst particles not having a direct contact to the gas phase, by diffusion through the ionomer material of through water.||x||Oxygen gain|
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