Conductivity Of Bipolar Plates Research Articles

Ion Implantation Combined with Heat Treatment Enables Excellent Conductivity and Corrosion Resistance of Stainless Steel Bipolar Plates for Hydrogen Fuel Cells.

316 L stainless steel is an ideal bipolar plate material for a proton exchange membrane fuel cell (PEMFC). However, the thickening of the passivation film on the stainless steel surface and the dissolution of corrosive ions during operation will affect the durability of the PEMFC. Herein, a heterogeneous layer is prepared on the surface of 316 L stainless steel through dual ion implantation of molybdenum ion and carbon ion combined with heat treatment to promote the corrosion resistance and conductivity of the bipolar plate. The ion implantation technique resulted in a uniform distribution of Mo and C elements on the surface of 316 L stainless steel, with a modified layer depth of about 70-80 nm. The electrical conductivity of the ion implanted samples was significantly improved, and the interfacial contact resistance was reduced from 464.25 mΩ × cm2 to 42.49 mΩ × cm2. Heat treatment enhances the surface homogenization, repairs the defects of irradiation damage, and improves the corrosion resistance of stainless steel. The corrosion current density of (Mo+C)-600 samples decreased from 1.21 × 10-8 A/cm2 to 2.95 × 10-9 A/cm2 under the long-term corrosion condition of 4 h. These results can provide guidance for the modification of stainless steel bipolar plates.

Performance and structure of Ti-doped amorphous carbon/CrN/Ti multilayer coating deposited on 316L stainless steel for use as bipolar plate in proton exchange membrane fuel cell

In order to improve the corrosion resistance and conductivity of stainless steel bipolar plates, three-layer Ti-doped amorphous carbon/CrN/Ti films were deposited on 316L stainless steel used for bipolar plates in PEMFCs. Titanium as the doped element added into amorphous carbon. Magnetron sputtering technology was used to deposit the films and control the titanium doped content by different titanium target currents. The structure transformation law of Ti content in amorphous carbon coating was studied. The application principle of corrosion resistance and conductivity of bipolar plates during the transformation of the coating structure from amorphous carbon to carbide was analyzed. With increasing Ti-doped content, the sp2/sp3 ratio increased, and the amorphous carbon film gradually transformed to titanium carbide matrix film. Characterization of the electrochemical corrosion confirmed that the anti-corrosion property of the films was closely related to the Ti-C phase and sp2/sp3 ratio. Ti-doped amorphous carbon/CrN/Ti film, which is built at 1A Ti target current, has the best corrosion current density. The interfacial contact resistance (ICR) first decreased and then increased with increasing Ti content. When excessive doping of titanium atoms makes the coating become a TiC matrix, the corrosion resistance and ICR property of the coating worsen. The film’s state of chemical bonds after electrochemical corrosion was tested by XPS to study the ICR increase mechanism. The Ti-doped amorphous carbon/CrN/Ti multilayer film can be used as a modified coating of 316L stainless steel bipolar plates for PEMFCs.

Properties of SS304 Modified by Nickel-Cobalt Alloy Coating with Cauliflower-Shaped Micro/Nano Structures in Simulated PEMFC Cathode Environment.

This study presents the corrosion behavior and surface properties of SS304 modified by electrodeposited nickel–cobalt (Ni–Co) alloy coating with cauliflower-shaped micro/nano structures (Ni–Co/SS304) in the simulated PEMFC cathodic environment. The hydrophobicity of the as-prepared Ni–Co alloy coating can be improved simply by low-temperature annealing. The morphology and composition of the Ni–Co/SS304 were analyzed and characterized by SEM, EDS, XRD, and XPS. The polarization, wettability, and ICR tests were respectively conducted to systemically evaluate the performance of Ni–Co/SS304 in the simulated PEMFC cathode environment. As revealed by the results, the Ni–Co/SS304 can maintain its hydrophobicity under hot-water droplets as high as 80 °C and demonstrates higher conductivity than the bare SS304 substrate before and after polarization (0.6 V vs. SCE, 5 h), which is of great significance to improve the surface hydrophobicity and conductivity of bipolar plates.

Anti-corrosion and conductivity of titanium diboride coating on metallic bipolar plates

Titanium diboride (TiB2) coatings are fabricated on 304 stainless steel bipolar plates using a cost-effective, high-energy micro-arc alloying technique to enhance their corrosion resistance and conductivity. Both the coated and bare bipolar plates are electrochemically tested in solutions to simulate the cathode and anode working environments of the proton exchange membrane fuel cell, namely 0.3 M H2SO4 and 2 ppm HF with air or hydrogen gas bubbled through. It is found that the compact TiB2 coating with metallurgical bonding to the substrate obviously increases the substrate corrosion potential in both the cathode and anode. Meanwhile, the coating significantly decreases the corresponding corrosion current density of the cathode and anode by three to four orders of magnitude compared to the substrate. The impedance and open circuit potential of the TiB2-coated steels during long-term immersion are significantly higher than those of the substrate. Furthermore, the contact resistance of the TiB2-coated sample after corrosion remains 19 mΩ cm2, which is lower than that of the bare steel. Therefore, TiB2 coating is demonstrated as a promising alternative for enhancing the corrosion resistance and conductivity of bipolar plates, owing to its high chemical stability and effective conductivity.