The service life and performance enhancement of proton exchange membrane fuel cells (PEMFC) critically depend on improving the corrosion resistance and electrical conductivity of their bipolar plates. This study systematically compares the mechanical properties of diamond-like carbon (DLC) film, WC/a-C nanocomposite film, and WC/a-C nanomultilayers and evaluated their corrosion resistance and electrical conductivity in a simulated PEMFC cathode environment (70 ℃, 1 mol/L H2SO4). The work aims to identify the film structure with superior overall performance, thereby providing a theoretical basis and practical guidance for the design of protective coatings on PEMFC bipolar plates. Three types of films are deposited on 316L stainless steel substrates by closed-field unbalanced magnetron sputtering. Adhesion strength, nanohardness, and elastic modulus are assessed through scratch testing and nanoindentation, respectively. Cross-sectional morphologies of the films are observed by field emission scanning electron microscopy (FESEM). For electrochemical characterization, the open circuit potentials (OCP) of the films are measured, and their corrosion resistances are evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The long-term durability and stability of the films are evaluated by potentiostatic polarization at a constant potential of +0.6 V. The interfacial contact resistance (ICR) values between the films and carbon paper are measured before and after the potentiostatic polarization testing under a pressure of 1.4 MPa. The conductivities of the film before and after corrosion and their variations are systematically evaluated. The corrosion morphologies are examined by FESEM, complemented by energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy to analyze the distribution of corrosion products. The results indicate that the WC/a-C nanomultilayers exhibits a hardness of 19 GPa, an elastic modulus of 287 GPa, a plasticity index (H3/E2) of 0.083 27 GPa, and an elastic index (H/E) of 0.066 20, demonstrating excellent mechanical properties. In terms of electrochemical performance, the WC/a-C nanomultilayers exhibits the highest open-circuit potential (329 mV) and the largest charge transfer resistance R2 (6.554 7×105 Ω·cm2). Its corrosion potential is 0.194 V, and its corrosion current density is 2.228×10-7 A/cm2, both superior to the DLC films (0.128 V, 2.960×10-7 A/cm2) and the WC/a-C nanocomposite film (0.174 V, 2.575×10-7 A/cm2), exhibiting the superior corrosion resistance among the three. The results of the potentiostatic polarization test further reveal that the WC/a-C nanomultilayers has the lowest stabilized corrosion current density (3.736 1×10-7 A/cm2) in the simulated PEMFC cathode environment, confirming its optimal long-term durability and stability. Furthermore, the WC/a-C nanomultilayers exhibits the lowest and most stable ICR values both before and after the potentiostatic polarization test, measuring 8.84 mΩ·cm2 (before) and 9.95 mΩ·cm2 (after), respectively, with a minimal change of only 1.11 mΩ·cm2. This indicates that it possesses not only excellent intrinsic conductivity but also outstanding corrosion resistance stability. Analysis by FESEM, EDS, and Raman spectroscopy confirms that the structure of the WC/a-C nanomultilayers effectively inhibits the penetration and diffusion of corrosive species and reduces the oxidative degradation of sp2-hybridized bonds, thereby mitigating corrosion damage of the film. In conclusion, the WC/a-C nanomultilayers exhibits outstanding corrosion resistance and electrical conductivity under the harsh operating conditions of PEMFC. It thus shows significant potential as a protective film for high-performance metallic bipolar plates.
Key words
DLC film /
WC/a-C nanocomposite film /
WC/a-C nanomultilayers /
bipolar plates /
corrosion performance /
conductivity
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Funding
National Natural Science Foundation of China (52365024); Natural Science Foundation of Gansu Province (25JRRA084); Major Science and Technology Project of Gansu Province (24ZD13GA018)
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