Corrosion Prevention of Chromium Nitride Coating with an Application to Bipolar Plate Materials

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The corrosion properties of chromium nitride (CrN) coating on nickel have been evaluated in order to improve the anti-corrosion of metallic bipolar plate materials with applications such as redox flow batteries. The CrN layers are prepared by nitridation of electroplated Cr layers with different thickness. The nitrogen content of CrN coating layers varies from 0.5 to 4.2 wt% depending on nitriding time and coating layer thickness. Electrochemical and chemical corrosion behaviors are investigated by potentiodynamic polarization test in 5% sulfuric acid and by immersion test in 50% sulfuric acid, respectively. Electrochemical analysis of corrosion potential and corrosion current density as well as passivation behavior and chemical corrosion rate prove conclusively that an intact thin CrN layer is more corrosion resistant than thicker layers where cracks are developed. Sheet resistance of CrN coating layers before and after the corrosion test exhibits no significant difference. The improved corrosion resistance and the excellent stability of CrN coating layers suggest an efficient anti-corrosion method for metallic bipolar plate materials.