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PECVD法原位滲氮表面改性鈦雙極板的性能

Evaluating the performances of surface-modified titanium bipolar plates using in situ nitriding by plasma-enhanced chemical vapor deposition

  • 摘要: 為了提升鈦雙極板的導電性和耐腐蝕性,利用氮氣等離子體原位滲氮法對鈦片(TA2)進行表面改性,制備了系列氮化鈦涂層,系統研究了反應溫度和滲氮時間對涂層表面形貌、疏水性、界面導電性和耐腐蝕性的影響。結果表明,溫度過高會導致氮化鈦生長過快,顆粒尺寸較大;溫度較低不利于表面反應,涂層不能完全覆蓋鈦基底;滲氮時間較短,表面生成不規則的納米生長核,致使涂層不平整、鈦基底裸露;滲氮時間過長,涂層呈階梯堆垛狀,平整度降低。650 °C下滲氮90 min制備的氮化鈦涂層(TiN-650-90)均勻平整,組成為TiN0.26;TiN-650-90的水接觸角提升至105.4°,表面疏水性有利于改善燃料電池的水管理性能;界面接觸電阻(ICR)隨加載壓力增大而降低,2.75 MPa時TiN-650-90的ICR穩定至6.5 mΩ·cm2,滿足美國能源部(DOE)要求(≤10 mΩ·cm2);TiN-650-90的腐蝕電流密度為0.56 μA·cm–2,–0.1 V恒電位下的電流密度為0.67 μA·cm–2,耐腐性和穩定性較鈦的明顯提升。該方法制備氮化鈦涂層表面改性鈦雙極板,具有沉積溫度低、速度快,疏水性、導電性和耐腐蝕性優良等優點,可為金屬雙極板表面改性提供方法借鑒和工藝參考。

     

    Abstract: In this study, the surface modification of titanium plates was performed using in situ nitriding via plasma-enhanced chemical vapor deposition to improve the conductivity and corrosion resistance of the plates. A series of titanium nitride (TiN) coatings were synthesized at different nitriding temperatures and durations. The influence of nitriding temperatures and durations on the surface morphology, hydrophobicity, interfacial conductivity, and corrosion resistance of the as-prepared coatings was investigated. The results indicated that faster growth and larger particle size of TiN are observed at higher temperatures. However, lower temperatures are unfavorable for surface reactions; thus, the coating cannot entirely cover the titanium substrate. Moreover, a shorter nitriding time results in irregular nanogrowth nuclei on the surface, leading to an uneven coating and bare titanium substrate. Conversely, longer nitriding time encourages the continuous accumulation of TiN nanoparticles and forms a uniform coating of the titanium substrate but decreases the flatness because of the stacking of the coatings due to the long nitriding time (120 min). The TiN coating prepared by nitriding at 650 °C for 90 min (TiN-650-90) is relatively compact and smooth with the composition of TiN0.26 and has an increased water contact angle of 105.4°. The change from hydrophilicity to hydrophobicity in TiN is beneficial to fuel cell water resistance. At a loading pressure of 1.5 MPa, the contact resistances of the coatings prepared at a nitriding time of 60 min can satisfy the U.S. Department of Energy requirement of less than 10 mΩ·cm2. Despite a contact resistance of 13.2 mΩ·cm2 for the TiN-650-90 coating, the contact resistance decreases with increasing loading pressure and is stable at 6.5 mΩ·cm2 under a loading pressure of 2.75 MPa. The corrosion current density of the TiN-650-90 coating is 0.56 μA·cm?2, and the corrosion potential positively shifts from ?0.37 to ?0.05 V at room temperature. The corrosion current density tested in the simulated operating environment of fuel cells is higher than that at room temperature but much lower than that of titanium (4.2 μA·cm?2). Furthermore, the current density is stable at 0.67 μA·cm?2 and at a ?0.1 V constant potential, indicating superior corrosion resistance and stability than titanium. The titanium bipolar plates modified by this method exhibit the advantages of relatively low deposition temperature, quick deposition speed, and good hydrophobicity, conductivity, and corrosion resistance. This work can pave the way for efficient surface modification of metal bipolar plates.

     

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