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.

NASA has a strong need to replace carbon as the diffusion media material in H2/O2 fuel cells to avoid corrosion during start/stop cycling. The use of H2/O2 fuel cells is critical in both lunar, satellite, and manned space travel applications. Historically, the use of metallic sinters and screen packs required the use of a thick membrane as the sinters and screens had large pore sizes and could not properly support a thin membrane. This leads to high resistances, and prevents NASA from taking advantage of membrane innovations such as Gore's Primea™ membrane, or GES's own thin Dimensionally Stable Membrane™. The thinner pore size and tighter tolerances of the proposed metallic papers will allow NASA to realize the performance and efficiency gains of these materials. Additionally, GES's own unique knowledge of wet-proofing metallic media will allow the elimination of carbon, making the fuel cell more durable and easing the requirement at start/stop.

GES already has two developed commercial electrolyzer products, analytical hydrogen and life support oxygen; as well as a third in development industrial hydrogen, and this material could prove beneficial in all three applications. In the analytical hydrogen application this material could supplant a multi-pieced screen-pack currently in use at the oxygen electrode, greatly reducing manufacturing labor. In GES's naval electrolyzers for life-support oxygen, this material could potentially replace a gas diffusion electrode support structure that consists of over three dozen parts. Finally in an emerging market, that GES is aggressively pursuing, that of water electrolysis for industrial hydrogen; this material may allow for the use of thinner membrane materials, thereby improving efficiency and giving GES a competitive advantage.

This is early/mid-stage (TRL 4) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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