Metal bipolar plates (BPs), as the core components of proton exchange membrane fuel cells (PEMFCs), directly determine the manufacturing cost and performance of the cells. However, in the high temperature and acidic working environment of fuel cells, the surface of metal bipolar plates is prone to oxidation, leading to a significant decrease in conductivity and corrosion resistance. In the study, we utilized a combination of arc and sputter deposition techniques to prepare Cr-Al-C coatings on stainless steel substrates. The phase transformation behavior of the Cr-Al-C coatings was investigated in situ using transmission electron microscopy. Through annealing techniques, Cr₂AlC MAX phase coatings with different degrees of crystallization and preferred orientations were obtained. The conductivity and corrosion resistance of these coatings were studied in the PEMFC working environment (pH=3 H₂SO₄+HF). The results demonstrate that all of the Cr₂AlC coatings significantly enhanced the performance of stainless steel 316L. The lowest interface contact resistance was 3.16 mΩ·cm², and the lowest corrosion current density was 2×10^-2 μA cm^-2. Simulations indicate that the excellent conductivity is attributed to the high density of electronic states of the Cr₂AlC MAX phase at the Fermi level. The superior corrosion resistance is attributed to the formation of a passive film on the coating surface after polarization tests, which effectively protects the substrate and improves its corrosion resistance. In addition, in order to improve the long-term conductivity and corrosion resistance of the BPs, we proposed a strategy of Sn solid solution MAX phase. These findings not only contribute to the design and development of new integrated MAX phase coating materials with conductivity and corrosion resistance, but also provide important support for the development of high-performance bipolar plate materials for PEMFCs.
 

Metal bipolar plates,MAX coating,Corrosion resistance,Conductivity