Metallic Fiber Papers for Gas Diffusion Layers
Hydrogen/oxygen polymer electrolyte fuel cells (PEMFCs) are an attractive means of generating electricity in lunar and space applications due to their high energy density. The PEMFC generally consists of an MEA supported on two sides by gas diffusion media. The gas diffusion media of choice is generally carbon-based in the form of a carbon fiber paper, or carbon cloth material. In the standard operating environment of a H2/O2 fuel cell the anode and cathode potentials are near 0 and 0.7-1.0, respectively. Carbon is generally stable in this potential range. Due to flooding, or during shut-down and start-up, oxygen may permeate the membrane and consume all of the hydrogen at the anode. If this occurs localized voltages above 1.6 V are possible, well above the carbon corrosion potential. For this reason GES proposes to replace the carbon fiber paper based gas diffusion media with an equivalent metallic fiber paper. GES has already demonstrated the electrochemical suitability of these materials by operating them in an electrolyzer for>3500 hours above 1.7 V. The major challenge is to wet-proof the metallic media to avoid flooding from fuel cell product water.
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