Preparation of carbon-coated stainless steels and their properties as bipolar plate materials of polymer electrolyte fuel cells

Abstract

In order to develop metal bipolar plates for polymer electrolyte fuel cells (PEFC), various grades of stainless steels (SUS304, SUS316, and SUS430) were coated with carbonaceous thin films by plasma-assisted chemical vapor deposition method. The resulting carbon-coated stainless steels were characterized by Raman spectroscopy, interfacial contact resistance (ICR) measurement, and scanning electron microscopy (SEM). Corrosion properties were examined by dynamic polarization measurement in H2SO4 solution. ICR values were decreased by carbon coating due to the deposition of a conductive carbonaceous thin film. The corrosion resistance of carbon-coated SUS304 and SUS430 was superior to that of carboncoated SUS316 at ambient temperature. Based on the SEM images obtained after dynamic polarization measurements, it was found that carbonaceous thin-film layers on SUS304 and SUS430 were dense and did not peel. At 80°C (simulated operating temperature of PEFCs), corrosion resistance of carbon-coated SUS304 was superior to that of carbon-coated SUS430. The influence of the stainless steel grade on the corrosion properties provided by carbon-coating was discussed in relation to the carbon deposition mechanism.