Effect of nitrogen pressure on the microstructure, conductivity, and corrosion resistance of ZrN-coated stainless steel as bipolar plate for proton exchange membrane fuel cell

Abstract

Zirconium nitride (ZrN) coatings were deposited on the stainless steel using multi-arc ion plating under varying nitrogen partial pressures (PN) ranging from 0.5 to 3.5 Pa. The effect of phase composition, microstructure, and surface morphology on the corrosion resistance and conductivity of the ZrN-coated stainless steel in a simulated proton exchange membrane fuel cell (PEMFC) cathode environment was systematically explored. XRD and TEM revealed that the columnar-structured ZrN coating mainly comprised the fcc-ZrN phase. The Zr3N4 phase was discovered near the substrate during coatings prepared at low nitrogen partial pressures. Surface defects were reduced at nitrogen partial pressures exceeding 2.5 Pa. The ZrN coating exhibited enhanced corrosion resistance and conductivity (ZrN-3.5, Ecorr = 0.307 V, Icorr = 2.085 × 10−7 A/cm2, Rct = 1.125 × 105 Ω·cm2) compared to bare stainless steel in the simulated PEMFC cathode environment. The presence of surface defects influenced the corrosion resistance, while differences in conductivity were related to the phase composition and microstructure of the coating. Thus, the findings indicate that ZrN coatings prepared under optimal deposition conditions can have potential applications in PEMFC bipolar plates.