PEMFC不锈钢双极板表面熔盐电沉积Cr/CrxN梯度涂层的生长机制及腐蚀行为研究

Stainless steel is promising candidate for bipolar plates of proton exchange memberane fuel cell. The main challenge of stainless steel, however, is the corrosion or passivity in working environments. Due to high corrosion resistance and electric conductivity, metallic nitride/carbide was attempted to protect stainless steel bipolar plates in recent years. This project proposes that electrochemical nitriding on electrodeposited-diffused Cr coatings on 316L stainless steel by pulse electrodeposition technology in the same molten salts electrolysis to prepare Cr/CrxN gradient coatings with no defect and metallurgical bonding. It is discussed the effect of the deposited parameters on the microstructure,morphology,corrosion resistance and contact resistance of Cr and Cr/CrxN coatings.The mechanism for reduction-diffusion of Cr3+ and oxidation-diffusion of N3- is studied to clarify the the thermodynamic and kinetics conditions for growth of Cr/CrxN coatings.As a result, the controllable preparation of Cr/CrxN gradient coating is achieved. The project provide theory evidence for the development corrosion resistant and conductive coating on stainless steel bipolar plates and has the positive influence on promotion of the application of stainless steel bipolar plates and commercialization of proton exchange memberane fuel cell.

不锈钢是质子交换膜燃料电池理想的双极板材料，但在其工作环境中易发生腐蚀或钝化。金属氮/碳化物具有良好的耐蚀性和导电性，是潜在的不锈钢双极板防护涂层。本项目在熔盐体系(含Cr3+和N3-)中采用脉冲电沉积技术，在316L不锈钢双极板表面阴极电沉积Cr涂层后，调整电位在Cr涂层表面进行阳极氮化，制备了"无缺陷"且与基体为冶金结合的Cr/CrxN梯度涂层。系统研究脉冲沉积参数对Cr/CrxN微观结构、形貌、腐蚀性能及接触电阻的影响规律，探索Cr3+的还原沉积-扩散及N3-的氧化-扩散机制，研究Cr及CrxN稳定生长的热力学及动力学条件，实现涂层的可控生长。本研究为发展具有优异耐蚀性和导电性的不锈钢双极板防护涂层提供理论依据，对推动不锈钢双极板的应用和质子交换膜燃料电池的商业化具有重要意义。

目前,石墨双极板的成本太高制约了质子交换膜燃料电池（PEMFC）的商业化应用。而极具应用前景的金属双极板在燃料电池工作环境中易于发生腐蚀或钝化。为解决金属双极板的上述问题，本项目在316L不锈钢双极板表面制备了具有良好的抗腐蚀性能与导电性能的Cr/Cr(CN)涂层。搭建了熔融盐共渗装置，掌握了实验参数对Cr涂层及碳氮共渗层微观组织与性能的影响规律，揭示了涂层及渗层的微观生长及扩散机制，探索了涂层在PEMFC模拟环境中的腐蚀行为。在以碳棒为对电极的LiCl-KCl- KNO2熔融盐体系中，在温度为600℃、电位为-1.9VAg/AgCl的条件下对316L不锈钢进行电化学碳氮共渗处理，渗层厚度约为8μm，主要组成相为CrN及Cr7C3; 采用磁控溅射方法在316L不锈钢表面沉积铬涂层，在基体温度为500℃、溅射电流为0.35A条件下沉积2h得到的铬涂层致密，抗腐蚀性能最优；对316L不锈钢双极板表面Cr涂层进行电化学碳氮共渗处理后得到Cr/Cr(CN)复合涂层，其在0.5mol/L H2SO4+2ppmF-腐蚀介质中腐蚀电流密度为0.21μA.cm2，在PEMFC阴极工作电位下（0.6VSCE）极化7200s后的极化电流密度仅为6μA.cm2，表明涂层有着较好的抗腐蚀性能；采用第一性原理计算比较了CrN和Cr2N的导电性与化学稳定性，从量子化学角度探索质子交换膜燃料电池金属双极板用金属陶瓷涂层的性能。