Zr2N2O Coating-Improved Corrosion Resistance for the Anodic Dissolution Induced by Cathodic Transient Potential

Xian-Zong Wang; Hong Luo; Triratna Muneshwar; Hong-Qiang Fan; Ken Cadien; Jing-Li Luo

doi:10.1021/acsami.8b13149

Zr₂N₂O Coating-Improved Corrosion Resistance for the Anodic Dissolution Induced by Cathodic Transient Potential

ACS Appl Mater Interfaces. 2018 Nov 21;10(46):40111-40124. doi: 10.1021/acsami.8b13149. Epub 2018 Nov 12.

Authors

Xian-Zong Wang¹, Hong Luo¹, Triratna Muneshwar¹, Hong-Qiang Fan², Ken Cadien¹, Jing-Li Luo¹

Affiliations

¹ Department of Chemical and Materials Engineering , University of Alberta , Edmonton , Alberta T6G 1H9 , Canada.
² Laboratory for Microstructures, Institute of Materials, School of Materials Science and Engineering , Shanghai University , Shanghai 200072 , P. R. China.

PMID: 30418733
DOI: 10.1021/acsami.8b13149

Abstract

Developing a corrosion-resistant and electrically conductive coating on metallic bipolar plates is essential to mitigate the performance degradation induced by the high cathodic transient potentials (CTPs) in the start-up/shut-down (SU/SD) processes of polymer electrolyte membrane fuel cells (PEMFCs). Herein, a zirconium oxynitride (Zr₂N₂O) coating prepared by atomic layer deposition was used to improve the corrosion resistance of 304 stainless steel (304 SS) toward anodic dissolution at various CTPs. Triangular potential pulses were applied to the specimens to simulate potential variations at the cathode side of the PEMFCs at SU/SD stages. Results show that the Zr₂N₂O coating can provide effective protection at a CTP as positive as 1.1 V versus Ag/AgCl. At all CTPs examined, the peak current density ( i_peak) extracted from the pulse test of the coated specimen (Zr₂N₂O/SS) is 2 orders of magnitude lower than that of uncoated 304 SS, indicating that the presence of the Zr₂N₂O coating remarkably increases the corrosion resistance for the anodic dissolution induced by CTPs. More importantly, upon increasing the CTPs, 304 SS experiences severe intergranular corrosion after 4050 pulses, whereas Zr₂N₂O/SS shows slight pitting corrosion. The quite low i_peak and the mitigated corrosion morphologies of Zr₂N₂O/SS confirm that incorporating oxygen into the protective coating for achieving a high oxidation resistance is a feasible way to restrain the anodic dissolution caused by high CTPs. Analysis of the electron energy level diagrams of the passive film suggests a protective coating with a wider valence band contributing to the improved corrosion resistance toward the transpassive dissolution.

Keywords: cathode transient potential; metal bipolar plates; plasma-enhanced atomic layer deposition; polymer electrolyte membrane fuel cell; transpassive dissolution; zirconium oxynitride coating.