Corrosion Resistance, Interfacial Contact Resistance, and Hydrophobicity of 316L Stainless Steel Bipolar Plates Coated with TiN/Amorphous Carbon Double Layer under Different Carbon Target Currents

To improve the corrosion, interfacial contact resistance, and hydrophobicity of bipolar plates used in proton-exchange membrane fuel cells, a series of TiN/amorphous carbon double-layer coatings was prepared on 316L stainless steel using magnetron sputtering. The structure of the amorphous carbon was controlled with different carbon target currents. The changed rules in the coating structure and performance under different carbon target currents were studied. Due to appropriate sputtering energy, an appropriate carbon target current reduced the grain boundary of the coating, resulting in a smoother surface, and increased the content of sp2 hybrid carbon. Compared with uncoated 316L stainless steel, the samples coated with amorphous carbon showed greatly improved corrosion resistance and conductivity. At a carbon target current of 5 A, low contact resistance and high corrosion resistance were achieved simultaneously. The significant improvement in corrosion resistance is attributed to the improvement in the quality of the coating surface. Due to the appropriate carbon target current increasing the content of sp2 hybrid carbon in the coating, the contact resistance of the coating was reduced. When the carbon target current was 5 A, the interfacial contact resistance of the sample was 3.9 mΩ·cm2, which is significantly lower than that of bare 316L stainless steel. After constant potential polarization testing, the coating still exhibited good conductivity.