Preparation and Corrosion Resistance of Cr/a-C Composite Coatings on the Surface of 304SS Bipolar Plates

LIU Chaokun; DONG Shaoyang; GAN Lang; REN Yanjie; CUI Xingcheng

doi:10.16490/j.cnki.issn.1001-3660.2026.04.004

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Surface Technology ›› 2026, Vol. 55 ›› Issue (4) : 40-51. DOI: 10.16490/j.cnki.issn.1001-3660.2026.04.004

Corrosion and Protection

Preparation and Corrosion Resistance of Cr/a-C Composite Coatings on the Surface of 304SS Bipolar Plates

LIU Chaokun¹, DONG Shaoyang¹, GAN Lang¹, REN Yanjie^1,2,*, CUI Xingcheng^3,*

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Abstract

304 stainless steel (304SS) is a highly promising material for proton exchange membrane fuel cell bipolar plates. To enhance the corrosion resistance of 304 stainless steel bipolar plates in the cathode environment of proton exchange membrane fuel cells, a Cr/a-C coating was deposited on the surface of the 304SS substrate with direct current magnetron sputtering technology at high temperatures. The microstructure and composition of the coating were characterized through scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The corrosion resistance of the coating in the cathode corrosion environment of a proton exchange membrane fuel cell (PEMFC) was evaluated with a series of electrochemical testing methods, including dynamic polarization testing, constant potential polarization testing, impedance spectroscopy experiments, and cyclic voltammetry. The results showed that the prepared coatings had tight interface contact with no pores or voids, and were firmly bonded to the substrate. The composite coating (304SS/Cr/C-750) deposited at 750 ℃ exhibited significant interdiffusion of components between the metallic Cr layer and the amorphous carbon layer. Through Tafel fitting of the dynamic potential polarization curve, it was found that the corrosion current density of the 304SS/Cr/C-750 coating was only 1.55×10^-8 A/cm², which was four orders of magnitude lower than that of the substrate, significantly enhancing the corrosion resistance of the substrate. After 10 hours of constant potential polarization at an applied potential of 0.6 V vs. SCE, the final current density stabilized at 2.16×10^-8 A/cm², meeting the 2025 target (DOE25) set by the U.S. Department of Energy. In a 1 000-hour impedance spectroscopy experiment, the coating maintained a high charge transfer resistance (R_ct) value, with the final R_ct value reaching 3.12×10⁶ Ω/cm², which was four orders of magnitude higher than the substrate (352.1 Ω·cm²), demonstrating exceptional long-term corrosion barrier performance. The diffusion coefficient in the equivalent circuit fitting of the coating varied between 0.83 and 0.87, indicating that the coating surface did not undergo significant changes. After undergoing 150 cycles of cyclic voltammetry testing, 304SS/Cr/C-750 exhibited the lowest peak current density (1.43×10^-6 A/cm²) and the lowest transferred charge quantity (3.76 mC/cm²), demonstrating its optimal electrochemical stability under dynamic operating conditions. The excellent corrosion resistance of 304SS/Cr/C-750 stems from the Cr/C interdiffusion "interlocking" structure formed at 750 ℃: it significantly enhances the interfacial bonding strength between the coating and the substrate and drastically reduces porosity, effectively blocking the penetration pathways of corrosive media (H⁺, SO₄^2-, etc.). Additionally, the high sp³ carbon content enhances the hardness and chemical inertness of the coating, while the low porosity and dense structure significantly impede ion and electron transport, thereby increasing membrane resistance. As a result, the coating maintains stable passivation in harsh acidic environments, effectively protecting the 304SS substrate from corrosion. In a simulated PEMFC cathode environment, the coating exhibits extremely low corrosion rates, excellent passivation stability, outstanding long-term impedance characteristics, and good dynamic load durability, fully meeting the application requirements for high-performance PEMFC bipolar plates.

Key words

PEMFC / metal bipolar plate / magnetron sputtering / amorphous carbon coating / electrochemical testing / corrosion resistance

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LIU Chaokun, DONG Shaoyang, GAN Lang, REN Yanjie, CUI Xingcheng. Preparation and Corrosion Resistance of Cr/a-C Composite Coatings on the Surface of 304SS Bipolar Plates[J]. Surface Technology. 2026, 55(4): 40-51

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