Composite-coated aluminum bipolar plates for PEM fuel cells

Aluminum-based bipolar plates for proton exchange membrane (PEM) fuel cells offer high strength and durability while weighing up to 65% less than stainless steel. To protect the aluminum from electrochemical corrosion while maintaining electrical conductivity, coatings that are a composite of a fluoropolymer and one or more conductive inorganic fillers were investigated. Titanium carbide (TiC) and graphite were found to be the best candidates for conductive fillers among six powders that were tested for acid and electrochemical stability. Composite coatings of graphite, TiC, and ethylene-tetrafluoroethylene (ETFE) were applied to the aluminum or ceramic substrates by wet spraying followed by heat treatment, and then tested for in-plane sheet resistance, through-plane area specific resistance (ASR), electrochemical corrosion resistance, flexural strength, and flexibility. The composite-coated aluminum plates meet the U.S. DOE targets for bipolar plates for in-plane conductivity, flexural strength, and cathodic corrosion resistance. The targets for through-plane ASR and anodic corrosion resistance were not met due to the spraying process producing an undesirable layered microstructure and also a microstructure with connected porosity and pinholes.

► TiC and graphite were identified as the best conductive filler powders.
► 3000 series Al alloys have the best corrosion resistance under fuel cell conditions.
► Composite-coated Al meets the DOE cathodic electrochemical corrosion target.
► Composite-coated Al performs better in a single cell stack than uncoated Al.