Corrosion-resistant, electrically conductive TiCN coatings for direct methanol fuel cell

Abstract

To improve the resistance to corrosion attack, hydrophobicity and the electrical conductivity of stainless steel (SS) bipolar plates for usage in direct methanol fuel cells (DMFC), a TiCN nanostructured coating, with the average thickness about 15 μm, was deposited onto a 316L SS substrate using the double cathode glow discharge plasma (DCGDP) method. Electrochemical measurements were carried out at 50 °C to determine the corrosion performance of both bare and TiCN-coated 316L SS in a simulated anode environment, replicating the operating conditions of a DMFC, with different methanol concentrations (0.05 M H2SO4 + 2 ppm HF + x M methanol (where x = 5, 10, 15, 20)). The results showed that the electrochemical degradation rate of both materials decreased with increasing methanol addition due to the restriction of proton mobility in the solution through the action of the methanol. At all the methanol concentrations of the test solutions, the TiCN coating had higher corrosion potentials and lower corrosion current densities than bare 316L SS, thus showing better corrosion resistance and enhanced electrochemical stability. Moreover, interfacial contact resistance (ICR) measurements revealed that the TiCN coating immersed in all test solutions with different methanol concentrations maintained a very low ICR value, which was advantageous to the operation of DMFC. Therefore, the TiCN coating, combining excellent corrosion resistance with good electrical conductivity, is considered to be an attractive candidate to serve as a protective surface for SS bipolar plates.