Deposition of gold–titanium and gold–nickel coatings on electropolished 316L stainless steel bipolar plates for proton exchange membrane fuel cells

The effects of electropolishing and coating deposition on electrical resistance and chemical stability were studied for the stainless steel bipolar plates in proton exchange membrane fuel cell (PEMFC). A series of 316L stainless steel plates, selected as the substrate for a proton exchange membrane fuel cell (PEMFC) bipolar plate, were electropolished with a solution of H₂SO₄ and H₃PO₄ at temperatures ranging from 70 to 110 °C. The surface regions of the two electropolished stainless steel plates were coated with gold and either a titanium or nickel layer using electron beam evaporation. The electropolished stainless steel plates coated in 2-μm thick gold with a 0.1-μm titanium or nickel interlayer showed remarkably smooth and uniform surface morphologies in AFM and FE-SEM images compared to the surfaces of the plates that were coated after mechanical polishing only. The electrical resistance and water contact angle of the deposited stainless steel bipolar plates are strongly dependent on the surface modification treatments (i.e., mechanical polishing versus electropolishing). ICP-MS and XPS results indicate that after electropolishing, the coating layers show excellent chemical stability after exposure to an H₂SO₄ solution of pH 3. Finally, it was concluded that before coating deposition, the surface modification using electropolishing was very suitable for enhancing the electrical property and chemical stability of the stainless steel bipolar plate.