DMFC环境下不锈钢双极板的表面NbC改性及耐蚀机理研究

双极板是连接单电池构成直接甲醇燃料电池（DMFC）的重要多功能组件，采用不锈钢双极板可大幅提高DMFC功率密度、降低成本。然而在DMFC运行环境下不锈钢因极化导致钝化膜生成并增厚，钝化膜的动态溶解-钝化过程中产生的微量金属离子污染膜电极组件，同时钝化膜的增厚增大了电池的欧姆压降，严重降低DMFC的总效率。为此，本项目提出利用碳化铌（NbC）的高耐蚀性和良好电传导特性改善不锈钢双极板表面状态。采用等离子表面合金化方法，通过工艺条件对改性层组织结构的影响研究，实现对致密NbC改性层可控制备。综合利用表面分析技术和电化学分析技术，研究NbC表面改性不锈钢在DMFC环境下的腐蚀钝化行为和表面钝化膜的结构组成；揭示甲醇浓度及阳极氧化产物对不锈钢耐蚀性和接触电阻的影响规律，阐明耐蚀机理；为促进DMFC表面改性不锈钢双极板的发展提供理论依据。

As multifunctional components of direct methanol fuel cell (DMFC), bipolar plates play an important role in connecting the anode of one cell to the cathode of the adjacent cell, supporting the cell stack, collecting current and providing a flow channel for fuel and oxidants. Stainless steels are potential candidates for bipolar plate materials to replace the traditional graphite bipolar plate with disadvantages of high cost, poor machining property and high brittleness. However, the stainless steel will be passivated and a passive film will form on its surface in DMFC operating environments. The metal ions produced by the dissolution-formation dynamic process of the passive film will further contaminate the electrode catalyst and result in the reduction of the cell performance. Besides, the incrassation of the passive film will increase the interfacial contact resistance (ICR) and accordingly reduce the power output of the fuel cell. Therefore, the niobium carbide with excellent chemical stability and high conductivity is put forward to improve the surface corrosion resistance and conductivity of stainless steel. The dense niobium carbide (NbC) modification layer is obtained through studying the effects of process conditions on the composition and structure of the modified layer. The passivation behaviours of the niobium carbide modified stainless steel and the passive film formed in the DMFC operating environments are analysed by surface analysis technique and electrochemical methods and the corrosion resistance mechanism will be described. The influence of methanol concentration and the anode oxidation products on the corrosion resistance and interfacial contact resistance (ICR) will be disclosed. The results of this project will offer theoretical foundation as well as some fundamental information for the research and development of stainless steel bipolar plates for DMFC.