NbC/Nb Film-Modified Stainless Steel Bipolar Plate for Proton Exchange Membrane Fuel Cell

The NbC/Nb composite film on SS304 as the bipolar plate of proton exchange membrane fuel cell (PEMFC) was prepared by magnetron sputtering deposition. Scanning electron microscopy and x-ray diffraction were used to characterize the morphology and composition of the film. Electrochemical tests under simulated PEMFC operating conditions (pH 3 H2SO4, 0.1 ppm HF at 80°C) show that the NbC/Nb composite film can provide better corrosion resistance. Potentiodynamic polarization tests reveal that NbC/Nb/SS304 shows lower corrosion current density and more positive corrosion potential than Nb/SS304 and SS304 substrate in simulated PEMFC environments. Potentiostatic tests were also performed at the potentials of 0.84 VSHE for 24 h to simulate the cathodic PEMFC conditions. NbC/Nb/SS304 reaches the lowest polarization current density of 1.01 × 10−7 A/cm2, which is lower than Nb/SS304 (1.83 × 10−7 A/cm2) and SS304 (1.11 × 10−4 A/cm2, four orders of magnitude as low). Under the pressure of 140 N/cm2, the interfacial contact resistance value of NbC/Nb/SS is 8.76 mΩ·cm2, which is significantly lower than Nb/SS304 (14.0 mΩ·cm2) and SS304 substrate (224 mΩ·cm2). After 0.84 VSHE potentiostatic polarization for 24 h, NbC/Nb/SS304 increase by just 0.42 mΩ·cm2 (from 8.76 mΩ·cm2 to 9.18 mΩ·cm2). However, Nb/SS304 increase by 1.2 mΩ·cm2 (from 14.0 mΩ·cm2 to 15.2 mΩ·cm2) and SS304 increase by 64 mΩ·cm2 (from 224 mΩ·cm2 to 288 mΩ·cm2). Moreover, the hydrophobic angle of NbC/Nb/SS304 is 116.5°, compared to Nb/SS304 (108.8°) and SS304 substrate SS304 (67.5°), which is beneficial to the drainage of the PEMFC.