DOT Coatings for Stainless Steel Bipolar Plates That Combine High Corrosion Resistance with Low Electrical Resistance

摘要

Within a fuel cell stack the bipolar plates are facing corrosive conditions and need to facilitate currents of over 2 A/cm~2. This paper discusses a coating technology for bipolar plates meeting performance metrics at an affordable price. Stainless steel (SS) is the preferred candidate for metal bipolar plates in polymer electrolyte membrane fuel cells (PEMFC). SS has good general corrosion resistance, high conductivity, suitable mechanical properties and good formability. Uncoated SS bipolar plates show a relatively high surface electrical contact resistance and ion leaching. The corrosion resistance relies on its native surface chromium oxide layer. This chromium oxide layer is fairly electrical resistive and its thickness grows over time. Uncoated SS shows a slow leaching of iron, nickel and chromium ions during PEMFC operations. The leached ions will poison the electrocatalyst and the membrane leading to performance degradation. The solution as presented is based on a hybrid coating technology with a post-treatment. The stable corrosion control is based on oxides, while conductivity is reached through conductive dots of a noble metal. Due to the potential, ions are preferably interacting with the noble metal dots. In that way a fairly thin coating can provide an effective corrosion barrier, also at higher operating voltages and over 5,000 hours testing time.