Acta Phys. -Chim. Sin. ›› 2015, Vol. 31 ›› Issue (2): 291-301.doi: 10.3866/PKU.WHXB201411262

• ELECTROCHEMISTRY AND NEW ENERGY • Previous Articles     Next Articles

Properties of Zr Nanocrystalline Coating on Ti Alloy Bipolar Plates in Simulated PEMFC Environments

QIAN Yang, XU Jiang   

  1. School of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, P. R. China
  • Received:2014-09-09 Revised:2014-11-26 Published:2015-01-26
  • Contact: XU Jiang E-mail:xujiang73@nuaa.edu.cn
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (51374130) and Aeronautical Science Foundation of China (2013ZE52058).

Abstract:

A zirconium nanocrystalline coating has been fabricated on a Ti-6A1-4V alloy bipolar plates using a double cathode glow discharge technique to improve the corrosion resistance and reduce the interfacial contact resistance in polymer electrolyte membrane fuel cells (PEMFCs). The microstructure of Zr coating was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The microstructure of the Zr coating was found to be continuous and compact; consisting of deposited and diffusion layers. The deposited layer was 30 μm thick and composed of equiaxed grains with an average grain size of around 15 nm, whereas the diffusion layer was 10 μm thick with a gradient distribution of alloying elements, which offered a smooth transition of mechanical properties that were suitable for improving the adhesion strength of the Zr coating on the Ti-6A1-4V substrate. The electrochemical behavior of the Zr coating was evaluated in 0.5 mol·L-1 H2SO4 solution containing 2 mg·L-1 of HF solution at 70 ℃ to simulate the environment found in a PEMFC. The solution was purged with H2 (simulated PEMFC anodic environment) or air (simulated PEMFC cathodic environment). The Ecorr of the deposited Zr nanocrystalline coating was much higher than that of the Ti-6A1-4V alloy in the simulated PEMFC environment. At the applied cathode (+0.6 V) potentials for PEMFCs, both the Zr nanocrystalline coating and Ti-6A1-4V alloy were in the passive region, but the passive current density of the as-deposited Zr nanocrystalline coating was four orders of magnitude lower than that of the Ti-6A1-4V alloy. At the applied anode (-0.1 V), the Zr nanocrystalline coating exhibited characteristic cathodic protection behavior. The results of electrochemical impedance spectroscopy (EIS) showed that the values of the capacitance semicircle, phase angle maximum and frequency range were larger than those of the Ti-6A1-4V alloy in the simulated PEMFC environment when the phase angle was near -80°. Moreover, the Zr nanocrystalline coating effectively improved the conductivity and hydrophobicity of the Ti-6A1- 4V alloy bipolar plate.

Key words: Proton exchange membrane fuel cell, Bipolar plate, Zr nanocrystalline coating, Corrosion resistance, Interfacial contact resistance

MSC2000: 

  • O646