【作者】 王利霞；

【导师】 孙俊才；

【作者基本信息】 大连海事大学 ， 载运工具运用工程， 2014， 博士

【摘要】 减少船舶尾气排放是《MARPOL公约》附则VI中改善海洋大气环境和港口环境的重点。聚合物电解质膜(PEM)燃料电池具有效率高、运行温度低、室温快速启动和环境友好等特点。大功率PEM燃料电池可作为商业船舶、港口船舶和内河船舶等的动力和船舶电网发电站,是减少船舶尾气排放的重要技术途径之(?)双极板是连接单电池构成大功率燃料电池电堆的重要的多功能组件,直接决定着燃料电池的能量密度、体积密度和成本。本文针对不锈钢双极板表面同时存在耐蚀性和导电性不足的问题,提出采用等离了表面合金化方法制备新型改性层,并研究其腐蚀行为和表面导电性等性能,探索改性层与耐蚀性、导电性的关系,以及表面耐腐蚀和表面导电机制。主要工作与结果如下：采用等离子表面合金化方法在商用304不锈钢(SS)表面分别制备出了钨、钼和铌的合金化渗扩改性层。改性层均匀致密且无微孔和微裂纹等缺陷,与基体的结合为良好的冶金结合。在模拟PEMFC环境中(70℃,0.05M H2SO4+2ppm HF溶液,通氢气模拟阳极环境,通空气模拟阴极环境),上述改性层均发生钝化现象,在燃料电池工作电位区处于钝化状态；合金化渗扩改性层的成分直接影响双极板的耐腐蚀性,由于铌在酸性环境中的优异耐蚀性,其合金化渗扩改性层表现出较好的耐蚀性和稳定性。在过渡金属合金化渗扩改性层的基础上,引入含氮或碳的反应气体,分别制备出铌氮化物和铌碳化物的化合物渗扩改性层。铌氮化物渗扩改性层是由多相β-Nb2N、δ’-NbN和δ-NbN铌氮化物表层和铌、氮扩散次表层所组成；铌碳化物渗扩改性层则由单相NbC表层和扩散次表层组成。在模拟PEMFC环境巾化合物改性层均提高不锈钢的耐腐蚀性、降低钝化电流密度、降低表面接触电阻、提高表面疏水性。铌氮化物和碳化物合金化渗扩改性层使304SS双极板在PEMFC条件下的腐蚀电流密度分别降到了0.127μA cm-2和0.058μA cm-2均低于1μAcm-2；恒电位极化后,铌碳化物合金化渗扩改性304SS的接触电阻达到9.04mΩ cm2,小于10mΩcm2,满足美国能源部(DOE)2015年的双极板目标性能要求利用ICP-AES技术对腐蚀溶液中溶解的金属离子进行分析,并结合XPS的分析结果探讨了不同的腐蚀环境对表面改性前后304SS钝化膜的成分、结构和厚度影响。结果表明,钝化膜结构和成分受腐蚀条件的控制,也直接决定改性层的耐腐蚀性和表面导电性。认为铌碳化物渗扩改性层钝化膜较薄,其中除了含有Nb氧化物外还有一定量的NbC,有利于表面导电性的提高。此外,本文还研究了含有不同甲醇浓度的酸性溶液的双极板性能,随着甲醇浓度的提高,铌碳化物合金化渗扩改性前后不锈钢的腐蚀速度均降低,铌碳化物渗扩改性304SS形成的钝化膜较薄,具有n型半导性质；而不锈钢形成的钝化膜较厚,具有双层结构一外层n-型半导体层和内层p-型半导体层。更多还原

【Abstract】 Reducing the exhaust emission of ships is the important contents of annex VI in MARPOL73/78convention, aiming to improve the environments of ocean and port. Polymer electrolyte membrane (PEM) fuel cells, which can be assembled into high-power stacks, have gained extensive attention as new power sources and electric stations for ships due to their relatively simple operating mechanisms, high efficiency and low emissions. Bipolar plates are one of the most crucial components, constituting the dominant share of the total weight and the total cost of the high-power fuel cell stack. Stainless steels are potential candidates for bipolar plate materials to replace the traditional graphite bipolar plate. However, bare stainless steels can not be successfully applied into a commercial PEMFC in terms of corrosion resistance and interfacial contact resistance. To address the insufficient corrosion resistance and high surface resistivity of stainless steel, a surface modification technique-plasma surface alloying method was utilized to make the surface modification of the commercial AISI304stainless steel (304SS). Following are the main study and results:Considering the good corrosion resistance of transition metal in acid environment, the tungsten, molybdenum and niobium alloying diffusion layer was respectively prepared on surface of304SS by plasma surface alloying method. The three modification layers are uniform in thickness, dense in microstructures without pinhole, micropore and microcracks, and well in metallurgical adhesion to the304SS substrate with no interfacial defects. The corrosion resistance were investigated and evaluated in simulated PEFMC environment (0.05M H2SO4+2ppm F" solution at70℃, purged with H2to simulate the anodic environment and purged with air to simulate the cathodic environment). The results showed that the modification layers were passivated in PEMFC environment. The corrosion resistance of stainless steel was affected by the composition of the modification layer, and the niobium alloying diffusion layer greately improved the corrosion resistance and stability of304SS.Transition metals nitrides and carbides usually have high electrical conductivity and good corrosion resistance, which can be made up the disadvantages of transition metal. On basis of the transition metal alloying diffusion layer, the niobium nitrid and niobium carbide alloying diffusion layers were respectively prepared on surface of304SS by introducing nitrogen or carbon containing gas to the plasma atmosphere. The niobium nitride alloying diffusion layer was comprised of β-Nb2N、δ-NbN and δ-NbN with a niobium nitride surface layer (8～9μm) and a Nb and N diffusion solid solution subsurface layer (1～2μm); The niobium carbide diffusion layer with a cubic NbC phase was comprised of surface layer (～6μm) and a Nb and C diffusion subsurface layer (-1μm). In simulated PEMFC environments, the compound modification layer improved the corrosion resistance, reduced the passivation current density and interfacial contact resistance (ICR), and increased the hydrophobicity of304SS. The niobium nitride and carbide diffusion layer considerably improves the corrosion resistance of304SS, which reduced the corrosion current density to0.127μA cm-2and0.058μA cm-2in simulated PEMFC environment, respectively. Moreover, the ICR of Nb-C304SS kept at9.04mΩ cm2after10h potentiostatic tests fulfilling the requirement of DOE in2015.The ICP-AES was used to detect the dissolution of metal ions in the corrosion solutions and in combination with the XPS analyses, the influence of corrosion environments on the composition, structure and thickness of passive film formed on304SS before and after surface modification were further discussed. The results reveal that the corrosion environments affected the composition and structure of passive film, which directly decided the corrosion resistance and conductivity of the modification layer. The passive film formed on the niobium carbide diffusion layer was composed of niobium oxide as well as NbC benefiting the improvement of surface conductivity.Besides, the performances of bipolar plate were investigated in aqueous acid methanol solutions with varied methanol concentrations. It was found that the corrosion resistance of the304SS (before and after surface modification) was better when the methanol content is higher. The passive films formed on Nb-C304SS were n-type semiconductor, while those formed on304SS were composed of a duplex electronic structure with an external n-type semiconductor layer and an internal p-type semiconductor layer.更多还原