Gas-distribution layers (GDLs) are water-management structures used in fuel cells and electrolyzers. GDLs are critical components that prevent flooding of the fuel cell electrode by product water, thus preserving open channels for reactant gas to reach the electrode. Typically, GDLs are electrically conductive papers (metal or carbon) having a fine pore structure. Extremely fine pores in some GDL materials are difficult to fully infiltrate with Teflon (PTFE). These materials are typically wet-proofed by coating with hydrophobic materials (e.g. PTFE). This is usually accomplished by immersing the raw paper in a PTFE emulsion. Completeness of wet-proofing by immersion in emulsion can be limited, because fine pores will filter out the PTFE particles.
The innovation is a method to infiltrate porous structures with PTFE, creating a highly hydrophobic structure whose internal pore structure is fully wet-proofed. Materials with extremely fine pores may be difficult to fully infiltrate with PTFE. This innovation improves the infiltration of PTFE by depositing the material in a plasma-assisted process.
A thin film coating of PTFE is deposited on the GDL paper to improve the wet-proofing of the paper. This process enables the PTFE to move through the small pores of the porous substrate, reaching the opposite surface and subsequent layers. The GDL paper is coated with a thin coating of PTFE utilizing an argon plasma beam under high vacuum. The PTFE travels and permeates the pores of the GDL.
Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) shows the cross-sectional area of the paper with the PTFE deposited throughout the bulk material, not just on the surface of the paper. By depositing the PTFE in this manner, the pores of the GDL are permeated throughout the bulk material. The coating will permeate through to the other side of the material and subsequent layers beneath the top sheet of GDL. Multiple samples can be stacked and coated simultaneously in this manner.
This work was done by William R. Bennett and Deborah L. Waters of Glenn Research Center.