Study on conductivity and corrosion resistance of N-doped and Cr/N co-doped DLC films on bipolar plates for PEMFC

In order to obtain films with good conductivity and high corrosion resistance for proton exchange membrane fuel cell (PEMFC) bipolar plate applications, N-doped and Cr/N co-doped diamond-like carbon (DLC) were deposited on stainless steel 316L and silicon wafer with constant nitrogen flow rate (4 sccm) and different Cr target power (0, 60, 90, 120 W). The electrical properties and corrosion resistance of the uncoated stainless steel and coated samples were tested under the simulated working environment of PEMFC. Scanning electron microscope (SEM) results show that the surface of Cr/N co-doped DLC film is smoother. Through the analysis of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) results, it is found that Cr/N co-doing DLC film is a combination of amorphous C, CrC, CN, Cr2N and nanocrystalline CrN. Contact resistance test indicates that the Cr/N co-doped DLC film (with Cr target power of 90 W) has the best electrical conductivity (9.20 m Omega cm(2) at 150 N/cm(2) pressure). Potentiodynamic polarization test shows that both N-doped DLC and Cr/N co-doped DLC films had better corrosion resistance (the corrosion current density could reach E-6 similar to E-7 A/cm(2)) than uncoated SS316L. To sum up, Cr/N co-doped DLC film (with Cr target power of 90 W) shows outstanding performance in both electrical conductivity and corrosion resistance, which is suitable for the surface treatment of stainless steel bipolar plates.