Preparation and characterization of TiC/a-C: H coating on the surface of metal bipolar plates in hydrogen fuel cells

Abstract:

Filtered cathodic vacuum arc deposition has an ultra-high ionization rate (nearly 100%), which can effectively suppress micro defects in the coatings optimize the microstructure of the coatings, and improve the performance of the coatings. In response to the poor corrosion resistance of metal bipolar plates in hydrogen fuel cells and their tendency to dissolve in acidic environments during long-term operation of proton exchange membrane fuel cells , we used a filtered cathodic vacuum arc deposition process to deposite a series of high conductivity and strong corrosion resistant nc-TiC/a-C: H coatings on the surface of metal bipolar plates in proton exchange membrane fuel cells In this paper, the effects of deposited ion energy on the conductivity and corrosion resistance of TiC/a-C: H coatings deposited on the surface of metal bipolar plates in hydrogen fuel cells were investigated. Nc-TiC/a-C: H nanocomposite coatings with a thickness of 0.52-1.05 μm were deposited on the surfaces of SS 304 stainless steel and monocrystalline silicon at negative substrate bias voltages of -100~-500 V with acetylene gas flow rate of 30 sccm by a dual bend filtered cathodic vacuum arc deposition process. The phase structure of the coatings were analyzed using X-ray diffraction (X pert pro MPD); The cross-section and surface microstructures of the coatings were characterized by field emission scanning electron microscopy (S-4800, Hitachi); Observation of high-resolution morphology of coatings using transmission electron microscopy (FEI CM200, Philips); The chemical element composition and chemical bond structure of the coating were analyzed by X-ray photoelectron spectroscopy (ESCALAB 250Xi, Thermofish); Raman spectroscopy (LavRAM Aramis, Horiba Jobin Yvon) characterizes the chemical structure distribution of carbon elements in the coating; The electrochemical workstation (IM6ex, Zahner elektrik) evaluated the corrosion resistance of coatings under simulated hydrogen fuel cell operating conditions. The surface contact resistance tester tested the contact resistance under different pressures; The study analyzed the changes in microstructure, coating composition, phase structure, corrosion resistance, and conductivity of TiC/a-C: H coatings under different negative bias voltages. The results show that the TiC/a-C: H composite coatings deposited under negative bias voltage of -100~-500 V exhibit dense low defect characteristics. The coatings are nanocrystalline/amorphous composite structure constructed by amorphous carbon coated nc-TiC nanocrystals. As the negative bias voltage increases, the size of nanocrystals in the coating increases from 3.3 nm to 7.9 nm. The optimal nc-TiC/a-C: H coating (coating deposited at negative bias -100 V) achieved an ultra-low corrosion current density of 0.0525 μA/cm_² in a simulated hydrogen fuel cell corrosion environment (80 ℃, 0.5 mol/L H₂SO₄+2 ppm HF aqueous solution), and achieved an extremely low ICR value of 1.49 mΩ/cm_² under a compression force of 1.4 MPa. Our results show that the nc-TiC/a-C:H coatings prepared by filtered cathodic vacuum arc deposition process can effectively improve the corrosion resistance and conductivity of SS 304 stainless steel bipolar plates within a wide negative bias range, meeting the performance requirements of DOE 2025 target for hydrogen fuel cell bipolar plates. This work open up a new avenue for the large-scale preparation of high-performance metal bipolar plate coatings.