Ni/Ni-Cr-P and Ni/Ni-Mo-Cr-P Electrodeposited Coatings As Bipolar Plate in Polymer Electrolyte Membrane Fuel Cell Environment

Abstract

Polymer electrolyte membrane (PEM) fuel cells are expected to play a major role in transporting humans and goods. However, one of major bottlenecks is the high materials and manufacturing cost. One way to lower the cost to a great extent is by replacing conventional graphitic bipolar plates with metallic bipolar plates (BPPs), as they costs around 30% of the total cost of stack1. That said, metallic BPPs have durability issues. Over time, they corrode and show higher interfacial contact resistance (ICR). In this work we attempt to engineer the surface of metallic BPPs, so that they perform for longer duration without degrading. To keep the process economical and commercially attractive, a bilayer coating of Ni followed by Ni-Cr-P alloy is pulsed electrodeposited on AISI 1020 low carbon steel. The electrodeposition process is optimized varying the process parameters, such as electrolyte composition, temperature and deposition current. Field emission scanning electron microscopy and energy dispersive x-ray spectroscopy are used to study the surface morphology and compositional analysis of coating, respectively. Variation in microstructure and composition the Ni/Ni-Cr-P coating is observed with change in process parameter such as pH and temperature. Corrosion studies were carried out on Ni/Ni-Cr-P coated samples using potentiodynamic technique in accelerated (0.5 M H2SO4 + 2 ppm HF) solution at 80ºC. Ni/Ni-Cr-P coated samples with higher Cr content exhibited better corrosion resistance behaviour in both cathodic (air-purging) as well as anodic (H2-purging) environment compared to the bare substrate. Long term durability of Ni/Ni-Cr-P coated samples and AISI 1020 low carbon steel samples were studied using potentiostatic polarization technique. Both coated and bare samples are placed in the accelerated electrolyte solution. Ni/Ni-Cr-P coated samples showed better durability with less change in current density, while bare samples completely disintegrate and precipitate into the solution within 2–3 hours in potentiostatic mode in both the environments. Ni/Ni-Cr-P coated sample show lower interfacial contact resistance (ICR) value than that of bare AISI 1020 steel samples. For better corrosion resistance and improvement in surface electrical property, Mo was included in the coating composition2. Ni/Ni-Mo-Cr-P coated samples show improved corrosion resistance than Ni/Ni-Cr-P coated samples and AISI 1020 low carbon steel bare samples in both anodic and cathodic PEM fuel cell environment. Reference: R. Taherian, J. Power Sources, 265, 370–390 (2014) http://dx.doi.org/10.1016/j.jpowsour.2014.04.081.H. Rashtchi et al., Fuel Cells, 16, 784–800 (2016) http://dx.doi.org/10.1002/fuce.201600062