Abstract
In here, we report on the pulse electrodeposition of nickel–chromium–phosphorous (Ni–Cr–P) coatings on AISI 1020 low carbon steel using an aqueous electrolyte consisting of NiCl2, CrCl3, and NaH2PO2. We evaluated the effectiveness of Ni–Cr–P coatings for polymer electrolyte membrane fuel cell metallic bipolar plates. Coatings deposited at pH 3.0 and room temperature show nearly three orders improvement in corrosion resistance compared to bare AISI 1020. The corrosion current (Icorr) of Ni–Cr–P samples coated at 25 °C is 1.16 × 10−4 A/cm2, while that of bare carbon steel is 1.05 × 10−2 A/cm2. The improvement in corrosion resistance is due to the increase in Cr content in the Ni–Cr–P coatings. Cr forms a stable oxide barrier layer and inhibits pitting corrosion. The interfacial contact resistance increases with an increase in Cr content and immersion time in the corrosion media. The increase in interfacial contact resistance is also due to the formation of a stable oxide barrier.
Highlights
Bipolar plate (BPP) plays a key role in a “polymer electrolyte membrane (PEM) fuel cell stack.” It prevents the interaction of the anodic and cathodic gases, distributes the anodic and cathodic gases uniformly, and electrically connects the adjacent cells
Polarization studies show that the corrosion resistance of Ni–Cr–P coatings increases by several orders of magnitude with an increase in Cr content
The interfacial contact resistance (ICR) of all Ni–Cr–P coatings increased with immersion time most likely due to the formation of hydrated oxide layers and subsequent formation of the pits on the surface of coated samples
Summary
Bipolar plate (BPP) plays a key role in a “polymer electrolyte membrane (PEM) fuel cell stack.” It prevents the interaction of the anodic and cathodic gases, distributes the anodic and cathodic gases uniformly, and electrically connects the adjacent cells. Metals such as titanium [3], copper [4], aluminum [5], stainless steel [6], carbon steel [7,8,9,10,11,12], and various other alloys [13, 14] have been evaluated for PEM fuel cell BPPs. Metals such as titanium [3], copper [4], aluminum [5], stainless steel [6], carbon steel [7,8,9,10,11,12], and various other alloys [13, 14] have been evaluated for PEM fuel cell BPPs Most of these studies conclude that the cost of manufacturing is low for metallic bipolar plates, the corrosion resistance is low and are not suitable for BPPs. The metallic bipolar plates corrode due to interaction with humid gases. When operated for longer duration SO42− and F− ions leach-out from the electrolyte {perfluorosulfonic acid (C9HF17O5S)} and make an aggressive environment near the BPP accelerating the corrosion rate
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