钛合金双极板表面纳米晶Zr涂层在质子交换膜燃料电池环境中的性能

为改善金属双极板在质子交换膜燃料电池(PEMFC)环境中的耐腐蚀性能及降低其界面接触电阻, 采用双阴极等离子溅射沉积技术, 在Ti-6A1-4V合金表面制备了纳米晶Zr 涂层. 利用扫描电子显微镜(SEM), X射线衍射(XRD)和透射电子显微镜(TEM)等微观分析手段对该涂层的组织结构进行了表征. 结果表明: 所制备的涂层具有沉积层和扩散层的双层结构, 其微观组织连续、致密. 在分别通入氢气/空气、70 ℃ 的0.5 mol·L^-1H₂SO₄+2 mg·L^-1 HF的溶液中, 对比研究了纳米晶Zr 涂层与Ti-6A1-4V合金在模拟电池的阳极/阴极工作环境中的电化学腐蚀性能. 动电位极化测试结果表明: 在模拟电池的阳极/阴极工作环境中, 纳米晶Zr 涂层的腐蚀电位均明显高于Ti-6A1-4V合金; 在阴极工作电极电位为+0.6 V下, 纳米晶Zr 涂层与Ti-6A1-4V合金均位于钝化区内, Zr 涂层的钝化电流密度较Ti-6A1-4V合金降低约4 个数量级; 而在阳极工作电极电位为-0.1 V下, 纳米晶Zr 涂层呈现出阴极保护特征. 电化学阻抗谱测试结果表明, 在0.5 mol·L^-1 H₂SO₄+2 mg·L^-1 HF的溶液中, 纳米晶Zr 涂层的容抗弧半径和相位角的最大值及其频率宽度均明显大于Ti-6A1-4V合金. 此外, 纳米晶Zr 涂层同时改善了Ti-6A1-4V合金的导电性与憎水性能.

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

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.